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Imboumy-Limoukou RK, Biteghe-Bi-Essone JC, Lendongo Wombo JB, Lekana-Douki SE, Rougeron V, Ontoua SS, Oyegue-Liabagui LS, Mbani Mpega Ntigui CN, Kouna LC, Lekana-Douki JB. Detection of Plasmodium falciparum in Saliva and Stool Samples from Children Living in Franceville, a Highly Endemic Region of Gabon. Diagnostics (Basel) 2023; 13:3271. [PMID: 37892092 PMCID: PMC10606300 DOI: 10.3390/diagnostics13203271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 09/04/2023] [Accepted: 09/14/2023] [Indexed: 10/29/2023] Open
Abstract
Due to the difficulty of obtaining blood samples, which is the invasive method that is currently used for the detection of Plasmodium spp., alternative diagnostic sampling methods that are effective and non-invasive are needed, particularly for long-term studies. Saliva and stool samples from malaria-infected individuals contain trace amounts of Plasmodium DNA and therefore could be used as alternatives. Malaria was screened using rapid diagnosis tests and confirmed via microscopy. Nested PCR tests targeting the Plasmodium falciparum-specific STEVOR gene were performed for blood, saliva and stool samples that were positive for malaria. Three hundred sixty-seven (367) children were enrolled and eighty (22.22%) were confirmed to be positive for malaria. Matched blood, saliva and stool samples were available for 35 children. By using blood smears as the gold standard for the diagnosis of malaria, our study indicates that Plasmodium DNA was more detectable in blood (100%) than in saliva (22.86%) and stools (14.29%). Applying qPCR to the STEVOR gene to detect Plasmodium falciparum DNA in saliva and stool samples cannot be considered as an alternative to the current malaria detection processes using blood specimens.
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Affiliation(s)
- Roméo Karl Imboumy-Limoukou
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
| | - Jean-Claude Biteghe-Bi-Essone
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
| | - Judicael Boris Lendongo Wombo
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
- Laboratoire de Biologie Moléculaire et Cellulaire (LABMC), Université des Sciences et Techniques de Masuku, Franceville BP 943, Gabon
| | - Sonia Etenna Lekana-Douki
- Unité des Maladies Virales Emergentes (UMVE), Centre International de Recherches Médicales de Franceville, Franceville BP 769, Gabon;
| | - Virginie Rougeron
- MIVEGEC, IRD, CNRS, University of Montpellier, 34900 Montpellier, France;
| | - Steede-Seinnat Ontoua
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
- Ecole Doctoral Régional en Infectiologie Tropical, Franceville BP 876, Gabon
| | - Lydie Sandrine Oyegue-Liabagui
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
- Ecole Doctoral Régional en Infectiologie Tropical, Franceville BP 876, Gabon
| | - Cherone Nancy Mbani Mpega Ntigui
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
- Ecole Doctoral Régional en Infectiologie Tropical, Franceville BP 876, Gabon
| | - Lady Charlène Kouna
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
| | - Jean-Bernard Lekana-Douki
- Unité Evolution Epidémiologie et Résistance Parasitaire (UNEEREP), Centre International de Recherches Médicales de Franceville (CIRMF), Franceville BP 769, Gabon; (J.-C.B.-B.-E.); (J.B.L.W.); (S.-S.O.); (L.S.O.-L.); (C.N.M.M.N.); (L.C.K.); (J.-B.L.-D.)
- Département de Parasitologie-Mycologie, Université des Sciences de la Santé, Libreville BP 4008, Gabon
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Pinda PG, Msaky DS, Muyaga LL, Mshani IH, Njalambaha RM, Kihonda J, Bwanaly H, Ngowo HS, Kaindoa EW, Koekemoer LL, Okumu FO. Relationships between biological age, distance from aquatic habitats and pyrethroid resistance status of Anopheles funestus mosquitoes in south-eastern Tanzania. Malar J 2022; 21:365. [PMID: 36461058 PMCID: PMC9719249 DOI: 10.1186/s12936-022-04389-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Accepted: 11/16/2022] [Indexed: 12/05/2022] Open
Abstract
BACKGROUND Malaria transmission can be highly heterogeneous between and within localities, and is influenced by factors such as survival and biting frequencies of Anopheles mosquitoes. This study investigated the relationships between the biological age, distance from aquatic habitats and pyrethroid resistance status of Anopheles funestus mosquitoes, which currently dominate malaria transmission in south-east Tanzania. The study also examined how such relationships may influence malaria transmission and control. METHODS Female An. funestus were collected in houses located 50-100 m, 150-200 m or over 200 m from the nearest known aquatic habitats. The mosquitoes were exposed to 1×, 5× and 10× the diagnostic doses of deltamethrin or permethrin, or to the synergist, piperonyl butoxide (PBO) followed by the pyrethroids, then monitored for 24 h-mortality. Ovaries of exposed and non-exposed mosquitoes were dissected to assess parity as a proxy for biological age. Adults emerging from larval collections in the same villages were tested against the same insecticides at 3-5, 8-11 or 17-20 days old. FINDINGS Mosquitoes collected nearest to the aquatic habitats (50-100 m) had the lowest mortalities compared to other distances, with a maximum of 51% mortality at 10× permethrin. For the age-synchronized mosquitoes collected as larvae, the insecticide-induced mortality assessed at both the diagnostic and multiplicative doses (1×, 5× and 10×) increased with mosquito age. The highest mortalities at 1× doses were observed among the oldest mosquitoes (17-20 days). At 10× doses, mortalities were 99% (permethrin) and 76% (deltamethrin) among 8-11 day-olds compared to 80% (permethrin) and 58% (deltamethrin) among 3-5 day-olds. Pre-exposure to PBO increased the potency of both pyrethroids. The proportion of parous females was highest among mosquitoes collected farthest from the habitats. CONCLUSION In this specific setting, older An. funestus and those collected farthest from the aquatic habitats (near the centre of the village) were more susceptible to pyrethroids than the younger ones and those caught nearest to the habitats. These findings suggest that pyrethroid-based interventions may remain at least moderately effective despite widespread pyrethroid-resistance, by killing the older, less-resistant and potentially-infective mosquitoes. Further studies should investigate how and whether these observations could be exploited to optimize malaria control in different settings.
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Affiliation(s)
- Polius G. Pinda
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania ,grid.11951.3d0000 0004 1937 1135School of Public Health, University of the Witwatersrand, Johannesburg, South Africa
| | - Dickson S. Msaky
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania
| | - Letus L. Muyaga
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania
| | - Issa H. Mshani
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania ,grid.8756.c0000 0001 2193 314XInstitute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, UK
| | - Rukiyah M. Njalambaha
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania
| | - Japhet Kihonda
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania
| | - Hamis Bwanaly
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania
| | - Halfan S. Ngowo
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania ,grid.8756.c0000 0001 2193 314XInstitute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, UK
| | - Emmanuel W. Kaindoa
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania ,grid.451346.10000 0004 0468 1595School of Life Sciences and Biotechnology, Nelson Mandela African Institution of Science and Technology, Arusha, United Republic of Tanzania
| | - Lizette L. Koekemoer
- Wits Research Institute for Malaria, Faculty of Health Sciences, Centre for Emerging Zoonotic and Parasitic Diseases, University of the Witwatersrand, National Institute for Communicable Diseases, Johannesburg, South Africa
| | - Fredros O. Okumu
- grid.414543.30000 0000 9144 642XEnvironmental Health and Ecological Sciences Department, Ifakara Health Institute, Morogoro, United Republic of Tanzania ,grid.451346.10000 0004 0468 1595School of Life Sciences and Biotechnology, Nelson Mandela African Institution of Science and Technology, Arusha, United Republic of Tanzania ,grid.11951.3d0000 0004 1937 1135School of Public Health, University of the Witwatersrand, Johannesburg, South Africa ,grid.8756.c0000 0001 2193 314XInstitute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, UK
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Su Yin M, Bicout DJ, Haddawy P, Schöning J, Laosiritaworn Y, Sa-angchai P. Added-value of mosquito vector breeding sites from street view images in the risk mapping of dengue incidence in Thailand. PLoS Negl Trop Dis 2021; 15:e0009122. [PMID: 33684130 PMCID: PMC7971869 DOI: 10.1371/journal.pntd.0009122] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 03/18/2021] [Accepted: 01/11/2021] [Indexed: 11/19/2022] Open
Abstract
Dengue is an emerging vector-borne viral disease across the world. The primary dengue mosquito vectors breed in containers with sufficient water and nutrition. Outdoor containers can be detected from geotagged images using state-of-the-art deep learning methods. In this study, we utilize such container information from street view images in developing a risk mapping model and determine the added value of including container information in predicting dengue risk. We developed seasonal-spatial models in which the target variable dengue incidence was explained using weather and container variable predictors. Linear mixed models with fixed and random effects are employed in our models to account for different characteristics of containers and weather variables. Using data from three provinces of Thailand between 2015 and 2018, the models are developed at the sub-district level resolution to facilitate the development of effective targeted intervention strategies. The performance of the models is evaluated with two baseline models: a classic linear model and a linear mixed model without container information. The performance evaluated with the correlation coefficients, R-squared, and AIC shows the proposed model with the container information outperforms both baseline models in all three provinces. Through sensitivity analysis, we investigate the containers that have a high impact on dengue risk. Our findings indicate that outdoor containers identified from street view images can be a useful data source in building effective dengue risk models and that the resulting models have potential in helping to target container elimination interventions.
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Affiliation(s)
- Myat Su Yin
- Faculty of ICT, Mahidol University, Nakhon Pathom, Thailand
| | - Dominique J. Bicout
- Biomathematics and Epidemiology, EPSP-TIMC, UMR CNRS 5525, Grenoble-Alpes University, VetAgro Sup, Grenoble, France
- Laue–Langevin Institute, Theory group, Grenoble, France
| | - Peter Haddawy
- Faculty of ICT, Mahidol University, Nakhon Pathom, Thailand
- Bremen Spatial Cognition Center, University of Bremen, Bremen, Germany
| | - Johannes Schöning
- Bremen Spatial Cognition Center, University of Bremen, Bremen, Germany
| | - Yongjua Laosiritaworn
- Information Technology Center, Department of Disease Control, Ministry of Public Health, Bangkok, Thailand
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Wu L, Mwesigwa J, Affara M, Bah M, Correa S, Hall T, Singh SK, Beeson JG, Tetteh KKA, Kleinschmidt I, D’Alessandro U, Drakeley C. Sero-epidemiological evaluation of malaria transmission in The Gambia before and after mass drug administration. BMC Med 2020; 18:331. [PMID: 33183292 PMCID: PMC7664049 DOI: 10.1186/s12916-020-01785-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2020] [Accepted: 09/16/2020] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND As The Gambia aims to achieve malaria elimination by 2030, serological assays are a useful surveillance tool to monitor trends in malaria incidence and evaluate community-based interventions. METHODS Within a mass drug administration (MDA) study in The Gambia, where reduced malaria infection and clinical disease were observed after the intervention, a serological sub-study was conducted in four study villages. Spatio-temporal variation in transmission was measured with a panel of recombinant Pf antigens on a multiplexed bead-based assay. Village-level antibody levels were quantified as under-15 sero-prevalence, sero-conversion rates, and age-adjusted antibody acquisition rates. Antibody levels prior to MDA were assessed for association with persistent malaria infection after community chemoprophylaxis. RESULTS Seasonal changes in antibodies to Etramp5.Ag1 were observed in children under 15 years in two transmission settings-the West Coast and Upper River Regions (4.32% and 31.30% Pf prevalence, respectively). At the end of the malaria season, short-lived antibody responses to Etramp5.Ag1, GEXP18, HSP40.Ag1, EBA175 RIII-V, and Rh2.2030 were lower amongst 1-15 year olds in the West Coast compared to the Upper River, reflecting known differences in transmission. Prior to MDA, individuals in the top 50th percentile of antibody levels had two-fold higher odds of clinical malaria during the transmission season, consistent with previous findings from the Malaria Transmission Dynamics Study, where individuals infected before the implementation of MDA had two-fold higher odds of re-infection post-MDA. CONCLUSIONS Serological markers can serve dual functions as indicators of malaria exposure and incidence. By monitoring age-specific sero-prevalence, the magnitude of age-stratified antibody levels, or identifying groups of individuals with above-average antibody responses, these antigens have the potential to complement conventional malaria surveillance tools. Further studies, particularly cluster randomised trials, can help establish standardised serological protocols to reliably measure transmission across endemic settings.
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Affiliation(s)
- Lindsey Wu
- Faculty of Infectious Tropical Diseases, Department of Infection Biology, London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT UK
| | - Julia Mwesigwa
- Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, Fajara, The Gambia
| | - Muna Affara
- Bernhard Nocht Institute for Tropical Medicine (BNITM), Arusha, Tanzania
| | - Mamadou Bah
- Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, Fajara, The Gambia
| | - Simon Correa
- Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, Fajara, The Gambia
| | - Tom Hall
- St. George’s University of London (SGUL), London, SW17 0RE UK
| | - Susheel K. Singh
- Department for Congenital Disorders, Statens Serum Institut, Copenhagen, Denmark
- Centre for Medical Parasitology at Department of Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark
| | - James G. Beeson
- Burnet Institute, Melbourne, Victoria 3004 Australia
- Central Clinical School, Monash University, Melbourne, Victoria Australia
- Department of Medicine, University of Melbourne, Melbourne, Victoria Australia
| | - Kevin K. A. Tetteh
- Faculty of Infectious Tropical Diseases, Department of Infection Biology, London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT UK
| | - Immo Kleinschmidt
- Faculty of Epidemiology and Population Health, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT UK
- School of Pathology, Wits Institute for Malaria Research, Faculty of Health Science, University of Witwatersrand, Johannesburg, South Africa
| | - Umberto D’Alessandro
- Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, Fajara, The Gambia
| | - Chris Drakeley
- Faculty of Infectious Tropical Diseases, Department of Infection Biology, London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT UK
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Chakraborty A, Chandru V. A Robust and Non-parametric Model for Prediction of Dengue Incidence. J Indian Inst Sci 2020. [DOI: 10.1007/s41745-020-00202-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Stresman G, Bousema T, Cook J. Malaria Hotspots: Is There Epidemiological Evidence for Fine-Scale Spatial Targeting of Interventions? Trends Parasitol 2019; 35:822-834. [PMID: 31474558 DOI: 10.1016/j.pt.2019.07.013] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 07/29/2019] [Accepted: 07/29/2019] [Indexed: 12/20/2022]
Abstract
As data at progressively granular spatial scales become available, the temptation is to target interventions to areas with higher malaria transmission - so-called hotspots - with the aim of reducing transmission in the wider community. This paper reviews literature to determine if hotspots are an intrinsic feature of malaria epidemiology and whether current evidence supports hotspot-targeted interventions. Hotspots are a consistent feature of malaria transmission at all endemicities. The smallest spatial unit capable of supporting transmission is the household, where peri-domestic transmission occurs. Whilst the value of focusing interventions to high-burden areas is evident, there is currently limited evidence that local-scale hotspots fuel transmission. As boundaries are often uncertain, there is no conclusive evidence that hotspot-targeted interventions accelerate malaria elimination.
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Affiliation(s)
- Gillian Stresman
- Infection Biology Department, London School of Hygiene and Tropical Medicine, London, UK.
| | - Teun Bousema
- Radboud University Medical Centre, Department of Microbiology, HB Nijmegen, The Netherlands.
| | - Jackie Cook
- Medical Research Council (MRC) Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, London, UK
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Dietrich D, Dekova R, Davy S, Fahrni G, Geissbühler A. Applications of Space Technologies to Global Health: Scoping Review. J Med Internet Res 2018; 20:e230. [PMID: 29950289 PMCID: PMC6041558 DOI: 10.2196/jmir.9458] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Revised: 03/21/2018] [Accepted: 04/22/2018] [Indexed: 12/27/2022] Open
Abstract
Background Space technology has an impact on many domains of activity on earth, including in the field of global health. With the recent adoption of the United Nations’ Sustainable Development Goals that highlight the need for strengthening partnerships in different domains, it is useful to better characterize the relationship between space technology and global health. Objective The aim of this study was to identify the applications of space technologies to global health, the key stakeholders in the field, as well as gaps and challenges. Methods We used a scoping review methodology, including a literature review and the involvement of stakeholders, via a brief self-administered, open-response questionnaire. A distinct search on several search engines was conducted for each of the four key technological domains that were previously identified by the UN Office for Outer Space Affairs’ Expert Group on Space and Global Health (Domain A: remote sensing; Domain B: global navigation satellite systems; Domain C: satellite communication; and Domain D: human space flight). Themes in which space technologies are of benefit to global health were extracted. Key stakeholders, as well as gaps, challenges, and perspectives were identified. Results A total of 222 sources were included for Domain A, 82 sources for Domain B, 144 sources for Domain C, and 31 sources for Domain D. A total of 3 questionnaires out of 16 sent were answered. Global navigation satellite systems and geographic information systems are used for the study and forecasting of communicable and noncommunicable diseases; satellite communication and global navigation satellite systems for disaster response; satellite communication for telemedicine and tele-education; and global navigation satellite systems for autonomy improvement, access to health care, as well as for safe and efficient transportation. Various health research and technologies developed for inhabited space flights have been adapted for terrestrial use. Conclusions Although numerous examples of space technology applications to global health exist, improved awareness, training, and collaboration of the research community is needed.
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Affiliation(s)
- Damien Dietrich
- Hopitaux Universitaires de Genève, eHealth and Telemedicine Division, Geneva, Switzerland
| | - Ralitza Dekova
- Hopitaux Universitaires de Genève, eHealth and Telemedicine Division, Geneva, Switzerland
| | - Stephan Davy
- Hopitaux Universitaires de Genève, eHealth and Telemedicine Division, Geneva, Switzerland
| | - Guillaume Fahrni
- Hopitaux Universitaires de Genève, eHealth and Telemedicine Division, Geneva, Switzerland
| | - Antoine Geissbühler
- Hopitaux Universitaires de Genève, eHealth and Telemedicine Division, Geneva, Switzerland
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Wilson AL, Pinder M, Bradley J, Donnelly MJ, Hamid-Adiamoh M, Jarju LBS, Jawara M, Jeffries D, Kandeh B, Rippon EJ, Salami K, D'Alessandro U, Lindsay SW. Emergence of knock-down resistance in the Anopheles gambiae complex in the Upper River Region, The Gambia, and its relationship with malaria infection in children. Malar J 2018; 17:205. [PMID: 29776361 PMCID: PMC5960171 DOI: 10.1186/s12936-018-2348-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 05/07/2018] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Insecticide resistance threatens malaria control in sub-Saharan Africa. Knockdown resistance to pyrethroids and organochlorines in Anopheles gambiae sensu lato (s.l.) is commonly caused by mutations in the gene encoding a voltage-gated sodium channel which is the target site for the insecticide. The study aimed to examine risk factors for knockdown resistance in An. gambiae s.l. and its relationship with malaria infection in children in rural Gambia. Point mutations at the Vgsc-1014 locus, were measured in An. gambiae s.l. during a 2-year trial. Cross-sectional surveys were conducted at the end of the transmission season to measure malaria infection in children aged 6 months-14 years. RESULTS Whilst few Anopheles arabiensis and Anopheles coluzzii had Vgsc-1014 mutations, the proportion of An. gambiae sensu stricto (s.s.) mosquitoes homozygous for the Vgsc-1014F mutation increased from 64.8 to 90.9% during the study. The Vgsc-1014S or 1014F mutation was 80% higher in 2011 compared to 2010, and 27% higher in the villages with indoor residual spraying compared to those without. An increase in the proportion of An. gambiae s.l. mosquitoes with homozygous Vgsc-1014F mutations and an increase in the proportion of An. gambiae s.s. in a cluster were each associated with increased childhood malaria infection. Homozygous Vgsc-1014F mutations were, however, most common in An. gambiae s.s. and almost reached saturation during the study meaning that the two variables were colinear. CONCLUSIONS As a result of colinearity between homozygous Vgsc-1014F mutations and An. gambiae s.s., it was not possible to determine whether insecticide resistance or species composition increased the risk of childhood malaria infection.
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Affiliation(s)
| | - Margaret Pinder
- Durham University, Durham, UK.,Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
| | - John Bradley
- London School of Hygiene and Tropical Medicine, London, UK
| | | | - Majidah Hamid-Adiamoh
- Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
| | | | - Musa Jawara
- Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
| | - David Jeffries
- Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
| | - Ballah Kandeh
- National Malaria Control Programme, Banjul, The Gambia
| | | | - Kolawole Salami
- Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
| | - Umberto D'Alessandro
- London School of Hygiene and Tropical Medicine, London, UK.,Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
| | - Steven W Lindsay
- Durham University, Durham, UK.,London School of Hygiene and Tropical Medicine, London, UK
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Durnez L, Pareyn M, Mean V, Kim S, Khim N, Menard D, Coosemans M, Sochantha T, Sluydts V. Identification and characterization of areas of high and low risk for asymptomatic malaria infections at sub-village level in Ratanakiri, Cambodia. Malar J 2018; 17:27. [PMID: 29334956 PMCID: PMC5769347 DOI: 10.1186/s12936-017-2169-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Accepted: 12/29/2017] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND Malaria elimination needs a concentration of activities towards identification of residual transmission foci and intensification of efforts to eliminate the last few infections, located in so-called 'malaria hotspots'. Previous work on characterizing malaria transmission hotspots has mainly focused on falciparum malaria and especially on symptomatic cases, while the malaria reservoir is expected to be mainly concentrated in the asymptomatic human population when transmission is low. For Plasmodium vivax, there has been less effort in identifying transmission hotspots. The main aim of this study was to uncover micro-epidemiological mechanisms of clustering of malaria infections at a sub-village level, based on geographical or behavioural features. METHODS A cross-sectional survey was performed in three villages within the highest malaria endemic province of Cambodia. The survey took place in the dry season, when the malaria reservoir is expected to be low and residing in the asymptomatic part of the population. Village and field locations of households were georeferenced, blood samples were taken from as many residents as possible and a short questionnaire probing for individual risk factors was taken. Asymptomatic malaria carriers were detected by PCR, and geographical clustering analysis (SaTScan) as well as risk factor analysis were performed. RESULTS A total of 1540 out of 1792 (86%) individuals were sampled. Plasmodial DNA was detected in 129 individuals (8.4%). P. vivax was most prevalent (5.5%) followed by Plasmodium malariae (2.1%) and Plasmodium falciparum (1.6%). Mixed infection occurred in 12 individuals. In two out of three villages geographical clustering of high and low malaria infection risk was clearly present. Cluster location and risk factors associated with the infection differed between the parasite species. Age was an important risk factor for the combined Plasmodium infections, while watching television at evenings was associated with increased odds of P. vivax infections [OR (CI): 1.86 (0.95-3.64)] and bed net use was associated with reduced odds of P. falciparum infections [OR (CI): 0.25 (0.077-0.80)]. CONCLUSIONS Clusters of malaria carriers were malaria species specific and often located remotely, outside village centres. As such, at micro-epidemiological level, malaria is not a single disease. Further unravelling the micro-epidemiology of malaria can enable programme managers to define the interventions likely to contribute to halt transmission in a particular hotspot location.
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Affiliation(s)
- Lies Durnez
- Institute of Tropical Medicine, Antwerp, Belgium. .,University of Antwerp, Antwerp, Belgium.
| | - Myrthe Pareyn
- Institute of Tropical Medicine, Antwerp, Belgium.,University of Antwerp, Antwerp, Belgium
| | - Vanna Mean
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Saorin Kim
- Institut Pasteur du Cambodge, Phnom Penh, Cambodia
| | - Nimol Khim
- Institut Pasteur du Cambodge, Phnom Penh, Cambodia
| | | | - Marc Coosemans
- Institute of Tropical Medicine, Antwerp, Belgium.,University of Antwerp, Antwerp, Belgium
| | - Tho Sochantha
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Vincent Sluydts
- Institute of Tropical Medicine, Antwerp, Belgium. .,University of Antwerp, Antwerp, Belgium.
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10
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Kenyeres Z, Tóth S, Sáringer-Kenyeres T, Márkus A, Bauer N. Ecology-based mapping of mosquito breeding sites for area-minimized BTI treatments. Biologia (Bratisl) 2017. [DOI: 10.1515/biolog-2017-0016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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11
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Hardy A, Makame M, Cross D, Majambere S, Msellem M. Using low-cost drones to map malaria vector habitats. Parasit Vectors 2017; 10:29. [PMID: 28088225 PMCID: PMC5237572 DOI: 10.1186/s13071-017-1973-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 01/05/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND There is a growing awareness that if we are to achieve the ambitious goal of malaria elimination, we must compliment indoor-based vector control interventions (such as bednets and indoor spraying) with outdoor-based interventions such as larval source management (LSM). The effectiveness of LSM is limited by our capacity to identify and map mosquito aquatic habitats. This study provides a proof of concept for the use of a low-cost (< $1000) drone (DJI Phantom) for mapping water bodies in seven sites across Zanzibar including natural water bodies, irrigated and non-irrigated rice paddies, peri-urban and urban locations. RESULTS With flying times of less than 30 min for each site, high-resolution (7 cm) georeferenced images were successfully generated for each of the seven sites, covering areas up to 30 ha. Water bodies were readily identifiable in the imagery, as well as ancillary information for planning LSM activities (access routes to water bodies by road and foot) and public health management (e.g. identification of drinking water sources, mapping individual households and the nature of their construction). CONCLUSION The drone-based surveys carried out in this study provide a low-cost and flexible solution to mapping water bodies for operational dissemination of LSM initiatives in mosquito vector-borne disease elimination campaigns. Generated orthomosaics can also be used to provide vital information for other public health planning activities.
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Affiliation(s)
- Andy Hardy
- Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, UK.
| | - Makame Makame
- Zanzibar Malaria Elimination Programme, Zanzibar Ministry of Health, Stone Town, Zanzibar, United Republic of Tanzania
| | - Dónall Cross
- Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, UK
| | - Silas Majambere
- Innovative Vector Control Consortium, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Mwinyi Msellem
- Zanzibar Malaria Elimination Programme, Zanzibar Ministry of Health, Stone Town, Zanzibar, United Republic of Tanzania
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12
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Pegha Moukandja I, Biteghe Bi Essone JC, Sagara I, Kassa Kassa RF, Ondzaga J, Lékana Douki JB, Bouyou Akotet M, Nkoghe Mba D, Touré Ndouo FS. Marked Rise in the Prevalence of Asymptomatic Plasmodium falciparum Infection in Rural Gabon. PLoS One 2016; 11:e0153899. [PMID: 27228058 PMCID: PMC4881998 DOI: 10.1371/journal.pone.0153899] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 04/05/2016] [Indexed: 11/29/2022] Open
Abstract
Control strategies implemented a decade ago led to a marked reduction in the prevalence of malaria in many countries. In Dienga, southeastern Gabon, the prevalence of microscopic P. falciparum infection was 7% in 2003, close to the pre-elimination threshold of 5%. The aim of this work was to determine the prevalence of P. falciparum infection in the same community a decade later. A cohort of 370 individuals aged from 3 to 85 years living in Dienga was investigated for P. falciparum infection; during six passages (P) in 15-month period. Demographic data were collected, along with behaviors and attitudes towards malaria. Plasmodium infection was diagnosed by microscopy (ME), followed by PCR to detect submicroscopic infection. The prevalence of P. falciparum infection in P1, P2, P3, P4, P5 and P6 was respectively 43.5% (25.1% ME+, 18.4% PCR+); 40.9% (27.0% ME+, 13.9% PCR+), 52.7% (26.1% ME+, 26.6% PCR+); 34.1% (14.1% ME+, 20% PCR+), 57.7% (25.4.% ME+, 32.3% PCR+); and 46.2% (21.4% ME+, 24.8% PCR+) with an overall average of 45.9% (95%CI [37.0–54.7], 23.2% ME+ and 22.7% PCR+). P4 and P5 prevalences were statically different throughout the six passages. Microscopic prevalence was significantly higher than that observed ten years ago (23% [n = 370] vs 7% [n = 323], p < 0.001). Asymptomatic infections were the most frequent (96%). Gametocytes were detected in levels ranging from 5.9% to 13.9%. Insecticide-treated nets, indoor residual insecticides, and self-medication were used by respectively 33.2% (95%CI [29.0–37.4]), 17.7% (95%CI [15.5–19.9]) and 12.1% (95%CI [10.6–13.6]) of the study population. A near-threefold increase in P. falciparum infection has been observed in a rural area of southeastern Gabon during a 10-year period. Most infections were asymptomatic, but these subjects likely represent a parasite reservoir. These findings call for urgent reinforcement of preventive measures.
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Affiliation(s)
- Irène Pegha Moukandja
- Centre International de Recherches Médicales de Franceville (CIRMF) B.P. 769 Franceville, Gabon
- Ecole Doctorale Régionale (EDR) en Infectiologie Tropicale, BP: 876 Franceville, Gabon
| | - Jean Claude Biteghe Bi Essone
- Centre International de Recherches Médicales de Franceville (CIRMF) B.P. 769 Franceville, Gabon
- Ecole Doctorale Régionale (EDR) en Infectiologie Tropicale, BP: 876 Franceville, Gabon
| | - Issaka Sagara
- Département d'Epidémiologie et des Affections Parasitaires, MRTC, Faculté de Médecine et d'Odontostomatologie, Université de Bamako, BP 1805 Bamako, Mali
| | | | - Julien Ondzaga
- Centre International de Recherches Médicales de Franceville (CIRMF) B.P. 769 Franceville, Gabon
| | - Jean-Bernard Lékana Douki
- Centre International de Recherches Médicales de Franceville (CIRMF) B.P. 769 Franceville, Gabon
- Ecole Doctorale Régionale (EDR) en Infectiologie Tropicale, BP: 876 Franceville, Gabon
- Département de Parasitologie-Mycologie Médecine Tropicale, Faculté de Médecine, Université des Sciences de la Santé, B.P. 4009 Libreville, Gabon
| | - Marielle Bouyou Akotet
- Département de Parasitologie-Mycologie Médecine Tropicale, Faculté de Médecine, Université des Sciences de la Santé, B.P. 4009 Libreville, Gabon
| | - Dieudonne Nkoghe Mba
- Centre International de Recherches Médicales de Franceville (CIRMF) B.P. 769 Franceville, Gabon
| | - Fousseyni S. Touré Ndouo
- Centre International de Recherches Médicales de Franceville (CIRMF) B.P. 769 Franceville, Gabon
- * E-mail:
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13
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Chang HH, Childs LM, Buckee CO. Variation in infection length and superinfection enhance selection efficiency in the human malaria parasite. Sci Rep 2016; 6:26370. [PMID: 27193195 PMCID: PMC4872237 DOI: 10.1038/srep26370] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 04/28/2016] [Indexed: 01/08/2023] Open
Abstract
The capacity for adaptation is central to the evolutionary success of the human malaria parasite Plasmodium falciparum. Malaria epidemiology is characterized by the circulation of multiple, genetically diverse parasite clones, frequent superinfection, and highly variable infection lengths, a large number of which are chronic and asymptomatic. The impact of these characteristics on the evolution of the parasite is largely unknown, however, hampering our understanding of the impact of interventions and the emergence of drug resistance. In particular, standard population genetic frameworks do not accommodate variation in infection length or superinfection. Here, we develop a population genetic model of malaria including these variations, and show that these aspects of malaria infection dynamics enhance both the probability and speed of fixation for beneficial alleles in complex and non-intuitive ways. We find that populations containing a mixture of short- and long-lived infections promote selection efficiency. Interestingly, this increase in selection efficiency occurs even when only a small fraction of the infections are chronic, suggesting that selection can occur efficiently in areas of low transmission intensity, providing a hypothesis for the repeated emergence of drug resistance in the low transmission setting of Southeast Asia.
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Affiliation(s)
- Hsiao-Han Chang
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Lauren M Childs
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
| | - Caroline O Buckee
- Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
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14
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Opondo KO, Weetman D, Jawara M, Diatta M, Fofana A, Crombe F, Mwesigwa J, D'Alessandro U, Donnelly MJ. Does insecticide resistance contribute to heterogeneities in malaria transmission in The Gambia? Malar J 2016; 15:166. [PMID: 26980461 PMCID: PMC4793517 DOI: 10.1186/s12936-016-1203-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 03/01/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Malaria hotspots, areas with consistently higher than average transmission, may become increasingly common as malaria declines. This phenomenon, currently observed in The Gambia, may be caused by several factors, including some related to the local vectors, whose contribution is poorly understood. METHODS Using WHO susceptibility bioassays, insecticide resistance status was determined in vector populations sampled from six pairs of villages across The Gambia, each pair contained a low and high prevalence village. RESULTS Three vector species were observed (23.5% Anopheles arabiensis, 31.2% Anopheles gambiae, 43.3% Anopheles coluzzii and 2.0% An. coluzzii × An. gambiae hybrids). Even at a fine scale, significant differences in species composition were detected within village pairs. Resistance to both DDT and deltamethrin was more common in An. gambiae, most markedly in the eastern part of The Gambia and partly attributable to differing frequencies of resistance mutations. The Vgsc-1014F target site mutation was strongly associated with both DDT (OR = 256.7, (95% CI 48.6-6374.3, p < 0.001) and deltamethrin survival (OR = 9.14, (95% CI 4.24-21.4, p < 0.001). A second target site mutation, Vgsc-1575Y, which co-occurs with Vgsc-1014F, and a metabolic marker of resistance, Gste2-114T, conferred additional survival benefits to both insecticides. DDT resistance occurred significantly more frequently in villages with high malaria prevalence (p = 0.025) though this did not apply to deltamethrin resistance. CONCLUSION Whilst causality of relationships requires further investigation, variation in vector species and insecticide resistance in The Gambia is associated with malaria endemicity; with a notably higher prevalence of infection and insecticide resistance in the east of the country. In areas with heterogeneous malaria transmission, the role of the vector should be investigated to guide malaria control interventions.
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Affiliation(s)
- Kevin Ochieng' Opondo
- Medical Research Council Unit, PO Box 273, Banjul, The Gambia.,Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK
| | - David Weetman
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Musa Jawara
- Medical Research Council Unit, PO Box 273, Banjul, The Gambia
| | - Mathurin Diatta
- Medical Research Council Unit, PO Box 273, Banjul, The Gambia
| | - Amfaal Fofana
- Medical Research Council Unit, PO Box 273, Banjul, The Gambia
| | - Florence Crombe
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK
| | - Julia Mwesigwa
- Medical Research Council Unit, PO Box 273, Banjul, The Gambia
| | - Umberto D'Alessandro
- Medical Research Council Unit, PO Box 273, Banjul, The Gambia.,London School of Hygiene and Tropical Medicine, London, UK.,Institute of Tropical Medicine, Antwerp, Belgium
| | - Martin James Donnelly
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, UK. .,London School of Hygiene and Tropical Medicine, London, UK.
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15
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Abstract
With increasing malaria control and goals of malaria elimination, many endemic areas are transitioning from high-to-low-to-no malaria transmission. Reductions in transmission will impact on the development of naturally acquired immunity to malaria, which develops after repeated exposure to Plasmodium spp. However, it is currently unclear how declining transmission and malaria exposure will affect the development and maintenance of naturally acquired immunity. Here we review the key processes which underpin this knowledge; the amount of Plasmodium spp. exposure required to generate effective immune responses, the longevity of antibody responses and the ability to mount an effective response upon re-exposure through memory responses. Lastly we identify research priorities which will increase our understanding of how changing transmission will impact on malarial immunity.
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16
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Ndiath MM, Cisse B, Ndiaye JL, Gomis JF, Bathiery O, Dia AT, Gaye O, Faye B. Application of geographically-weighted regression analysis to assess risk factors for malaria hotspots in Keur Soce health and demographic surveillance site. Malar J 2015; 14:463. [PMID: 26581562 PMCID: PMC4652414 DOI: 10.1186/s12936-015-0976-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 10/28/2015] [Indexed: 12/01/2022] Open
Abstract
Background In Senegal, considerable efforts have been made to reduce malaria morbidity and mortality during the last decade. This resulted in a marked decrease of malaria cases. With the decline of malaria cases, transmission has become sparse in most Senegalese health districts. This study investigated malaria hotspots in Keur Soce sites by using geographically-weighted regression. Because of the occurrence of hotspots, spatial modelling of malaria cases could have a considerable effect in disease surveillance. Methods This study explored and analysed the spatial relationships between malaria occurrence and socio-economic and environmental factors in small communities in Keur Soce, Senegal, using 6 months passive surveillance. Geographically-weighted regression was used to explore the spatial variability of relationships between malaria incidence or persistence and the selected socio-economic, and human predictors. A model comparison of between ordinary least square and geographically-weighted regression was also explored. Vector dataset (spatial) of the study area by village levels and statistical data (non-spatial) on malaria confirmed cases, socio-economic status (bed net use), population data (size of the household) and environmental factors (temperature, rain fall) were used in this exploratory analysis. ArcMap 10.2 and Stata 11 were used to perform malaria hotspots analysis. Results From Jun to December, a total of 408 confirmed malaria cases were notified. The explanatory variables-household size, housing materials, sleeping rooms, sheep and distance to breeding site returned significant t values of −0.25, 2.3, 4.39, 1.25 and 2.36, respectively. The OLS global model revealed that it explained about 70 % (adjusted R2 = 0.70) of the variation in malaria occurrence with AIC = 756.23. The geographically-weighted regression of malaria hotspots resulted in coefficient intercept ranging from 1.89 to 6.22 with a median of 3.5. Large positive values are distributed mainly in the southeast of the district where hotspots are more accurate while low values are mainly found in the centre and in the north. Conclusion Geographically-weighted regression and OLS showed important risks factors of malaria hotspots in Keur Soce. The outputs of such models can be a useful tool to understand occurrence of malaria hotspots in Senegal. An understanding of geographical variation and determination of the core areas of the disease may provide an explanation regarding possible proximal and distal contributors to malaria elimination in Senegal.
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Affiliation(s)
- Mansour M Ndiath
- Service Parasitologie, Université Cheikh Anta Diop, Dakar, Senegal.
| | - Badara Cisse
- Service Parasitologie, Université Cheikh Anta Diop, Dakar, Senegal. .,London School of Hygiene and Tropical Medicine, London, UK.
| | | | - Jules F Gomis
- Service Parasitologie, Université Cheikh Anta Diop, Dakar, Senegal.
| | | | - Anta Tal Dia
- Institut de santé et de développement, UCAD, Dakar, Senegal.
| | - Oumar Gaye
- Service Parasitologie, Université Cheikh Anta Diop, Dakar, Senegal.
| | - Babacar Faye
- Service Parasitologie, Université Cheikh Anta Diop, Dakar, Senegal. .,Unité Mixte Internationale « Environnement, Santé, Sociétés » (UMI3189 ESS), CNRS-UCAD-CNRST-USTTB-UGB, Dakar, Senegal.
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17
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Monitoring disease trends using hospital traffic data from high resolution satellite imagery: a feasibility study. Sci Rep 2015; 5:9112. [PMID: 25765943 PMCID: PMC4357853 DOI: 10.1038/srep09112] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 02/12/2015] [Indexed: 11/09/2022] Open
Abstract
Challenges with alternative data sources for disease surveillance include differentiating the signal from the noise, and obtaining information from data constrained settings. For the latter, events such as increases in hospital traffic could serve as early indicators of social disruption resulting from disease. In this study, we evaluate the feasibility of using hospital parking lot traffic data extracted from high-resolution satellite imagery to augment public health disease surveillance in Chile, Argentina and Mexico. We used archived satellite imagery collected from January 2010 to May 2013 and data on the incidence of respiratory virus illnesses from the Pan American Health Organization as a reference. We developed dynamical Elastic Net multivariable linear regression models to estimate the incidence of respiratory virus illnesses using hospital traffic and assessed how to minimize the effects of noise on the models. We noted that predictions based on models fitted using a sample of observations were better. The results were consistent across countries with selected models having reasonably low normalized root-mean-squared errors and high correlations for both the fits and predictions. The observations from this study suggest that if properly procured and combined with other information, this data source could be useful for monitoring disease trends.
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18
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Hardy A, Mageni Z, Dongus S, Killeen G, Macklin MG, Majambare S, Ali A, Msellem M, Al-Mafazy AW, Smith M, Thomas C. Mapping hotspots of malaria transmission from pre-existing hydrology, geology and geomorphology data in the pre-elimination context of Zanzibar, United Republic of Tanzania. Parasit Vectors 2015; 8:41. [PMID: 25608875 PMCID: PMC4307680 DOI: 10.1186/s13071-015-0652-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 01/11/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Larval source management strategies can play an important role in malaria elimination programmes, especially for tackling outdoor biting species and for eliminating parasite and vector populations when they are most vulnerable during the dry season. Effective larval source management requires tools for identifying geographic foci of vector proliferation and malaria transmission where these efforts may be concentrated. Previous studies have relied on surface topographic wetness to indicate hydrological potential for vector breeding sites, but this is unsuitable for karst (limestone) landscapes such as Zanzibar where water flow, especially in the dry season, is subterranean and not controlled by surface topography. METHODS We examine the relationship between dry and wet season spatial patterns of diagnostic positivity rates of malaria infection amongst patients reporting to health facilities on Unguja, Zanzibar, with the physical geography of the island, including land cover, elevation, slope angle, hydrology, geology and geomorphology in order to identify transmission hot spots using Boosted Regression Trees (BRT) analysis. RESULTS The distribution of both wet and dry season malaria infection rates can be predicted using freely available static data, such as elevation and geology. Specifically, high infection rates in the central and southeast regions of the island coincide with outcrops of hard dense limestone which cause locally elevated water tables and the location of dolines (shallow depressions plugged with fine-grained material promoting the persistence of shallow water bodies). CONCLUSIONS This analysis provides a tractable tool for the identification of malaria hotspots which incorporates subterranean hydrology, which can be used to target larval source management strategies.
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Affiliation(s)
- Andrew Hardy
- Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, UK.
| | - Zawadi Mageni
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, United Republic of Tanzania.
| | - Stefan Dongus
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland.
| | - Gerry Killeen
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, United Republic of Tanzania.
- Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, UK.
| | - Mark G Macklin
- Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, UK.
| | - Silas Majambare
- Environmental Health and Ecological Sciences, Ifakara Health Institute, Ifakara, United Republic of Tanzania.
- Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, UK.
| | - Abdullah Ali
- Zanzibar Malaria Elimination Program, Zanzibar, United Republic of Tanzania.
| | - Mwinyi Msellem
- Zanzibar Malaria Elimination Program, Zanzibar, United Republic of Tanzania.
| | | | - Mark Smith
- School of Geography, University of Leeds, Leeds, UK.
| | - Chris Thomas
- Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, UK.
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19
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Nixon CP, Nixon CE, Arsyad DS, Chand K, Yudhaputri FA, Sumarto W, Wangsamuda S, Asih PB, Marantina SS, Wahid I, Han G, Friedman JF, Bangs MJ, Syafruddin D, Baird JK. Distance to Anopheles sundaicus larval habitats dominant among risk factors for parasitemia in meso-endemic Southwest Sumba, Indonesia. Pathog Glob Health 2014; 108:369-80. [PMID: 25495283 DOI: 10.1179/2047773214y.0000000167] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
BACKGROUND The decline in intensity of malaria transmission in many areas now emphasizes greater importance of understanding the epidemiology of low to moderate transmission settings. Marked heterogeneity in infection risk within these populations creates opportunities to understand transmission and guide resource allocation to greater impact. METHODS In this study, we examined spatial patterns of malaria transmission in a hypo- to meso-endemic area of eastern Indonesia using malaria prevalence data collected from a cross-sectional socio-demographic and parasitological survey conducted from August to November 2010. An entomological survey performed in parallel, identified, mapped, and monitored local anopheline larval habitats. RESULTS A single spatial cluster of higher malaria prevalence was detected during the study period (relative risk=2.13; log likelihood ratio=20.7; P<0.001). In hierarchical multivariate regression models, risk of parasitemia was inversely correlated with distance to five Anopheles sundaicus known larval habitats [odds ratio (OR)=0.21; 95% confidence interval (CI)=0.14-0.32; P<0.001], which were located in a geographically restricted band adjacent to the coastline. Increasing distance from these sites predicted increased hemoglobin level across age strata after adjusting for confounders (OR=1.6; 95% CI=1.30-1.98; P<0.001). CONCLUSION Significant clustering of malaria parasitemia in close proximity to very specific and relatively few An. sundaicus larval habitats has direct implications for local control strategy, policy, and practice. These findings suggest that larval source management could achieve profound if not complete impact in this region.
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20
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Louis VR, Phalkey R, Horstick O, Ratanawong P, Wilder-Smith A, Tozan Y, Dambach P. Modeling tools for dengue risk mapping - a systematic review. Int J Health Geogr 2014; 13:50. [PMID: 25487167 PMCID: PMC4273492 DOI: 10.1186/1476-072x-13-50] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Accepted: 11/30/2014] [Indexed: 12/04/2022] Open
Abstract
Introduction The global spread and the increased frequency and magnitude of epidemic dengue in the last 50 years underscore the urgent need for effective tools for surveillance, prevention, and control. This review aims at providing a systematic overview of what predictors are critical and which spatial and spatio-temporal modeling approaches are useful in generating risk maps for dengue. Methods A systematic search was undertaken, using the PubMed, Web of Science, WHOLIS, Centers for Disease Control and Prevention (CDC) and OvidSP databases for published citations, without language or time restrictions. A manual search of the titles and abstracts was carried out using predefined criteria, notably the inclusion of dengue cases. Data were extracted for pre-identified variables, including the type of predictors and the type of modeling approach used for risk mapping. Results A wide variety of both predictors and modeling approaches was used to create dengue risk maps. No specific patterns could be identified in the combination of predictors or models across studies. The most important and commonly used predictors for the category of demographic and socio-economic variables were age, gender, education, housing conditions and level of income. Among environmental variables, precipitation and air temperature were often significant predictors. Remote sensing provided a source of varied land cover data that could act as a proxy for other predictor categories. Descriptive maps showing dengue case hotspots were useful for identifying high-risk areas. Predictive maps based on more complex methodology facilitated advanced data analysis and visualization, but their applicability in public health contexts remains to be established. Conclusions The majority of available dengue risk maps was descriptive and based on retrospective data. Availability of resources, feasibility of acquisition, quality of data, alongside available technical expertise, determines the accuracy of dengue risk maps and their applicability to the field of public health. A large number of unknowns, including effective entomological predictors, genetic diversity of circulating viruses, population serological profile, and human mobility, continue to pose challenges and to limit the ability to produce accurate and effective risk maps, and fail to support the development of early warning systems. Electronic supplementary material The online version of this article (doi:10.1186/1476-072X-13-50) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Valérie R Louis
- Institute of Public Health, Heidelberg University Medical School, Heidelberg, Germany.
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Bousema T, Okell L, Felger I, Drakeley C. Asymptomatic malaria infections: detectability, transmissibility and public health relevance. Nat Rev Microbiol 2014; 12:833-40. [PMID: 25329408 DOI: 10.1038/nrmicro3364] [Citation(s) in RCA: 441] [Impact Index Per Article: 44.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Most Plasmodium falciparum infections that are detected in community surveys are characterized by low-density parasitaemia and the absence of clinical symptoms. Molecular diagnostics have shown that this asymptomatic parasitic reservoir is more widespread than previously thought, even in low-endemic areas. In this Opinion article, we describe the detectability of asymptomatic malaria infections and the relevance of submicroscopic infections for parasite transmission to mosquitoes and for community interventions that aim at reducing transmission. We argue that wider deployment of molecular diagnostic tools is needed to provide adequate insight into the epidemiology of malaria and infection dynamics to aid elimination efforts.
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Affiliation(s)
- Teun Bousema
- 1] London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK. [2] Radboud University Medical Centre, 6525 GA Nijmegen, The Netherlands
| | - Lucy Okell
- Imperial College, London, London SW7 2AZ, UK
| | | | - Chris Drakeley
- London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK
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Rumisha SF, Smith T, Abdulla S, Masanja H, Vounatsou P. Modelling heterogeneity in malaria transmission using large sparse spatio-temporal entomological data. Glob Health Action 2014; 7:22682. [PMID: 24964782 PMCID: PMC4071307 DOI: 10.3402/gha.v7.22682] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Revised: 05/02/2014] [Accepted: 05/10/2014] [Indexed: 11/14/2022] Open
Abstract
Background Malaria transmission is measured using entomological inoculation rate (EIR), number of infective mosquito bites/person/unit time. Understanding heterogeneity of malaria transmission has been difficult due to a lack of appropriate data. A comprehensive entomological database compiled by the Malaria Transmission Intensity and Mortality Burden across Africa (MTIMBA) project (2001–2004) at several sites is the most suitable dataset for studying malaria transmission–mortality relations. The data are sparse and large, with small-scale spatial–temporal variation. Objective This work demonstrates a rigorous approach for analysing large and highly variable entomological data for the study of malaria transmission heterogeneity, measured by EIR, within the Rufiji Demographic Surveillance System (DSS), MTIMBA project site in Tanzania. Design Bayesian geostatistical binomial and negative binomial models with zero inflation were fitted for sporozoite rates (SRs) and mosquito density, respectively. The spatial process was approximated from a subset of locations. The models were adjusted for environmental effects, seasonality and temporal correlations and assessed based on their predictive ability. EIR was calculated using model-based predictions of SR and density. Results Malaria transmission was mostly influenced by rain and temperature, which significantly reduces the probability of observing zero mosquitoes. High transmission was observed at the onset of heavy rains. Transmission intensity reduced significantly during Year 2 and 3, contrary to the Year 1, pronouncing high seasonality and spatial variability. The southern part of the DSS showed high transmission throughout the years. A spatial shift of transmission intensity was observed where an increase in households with very low transmission intensity and significant reduction of locations with high transmission were observed over time. Over 68 and 85% of the locations selected for validation for SR and density, respectively, were correctly predicted within 95% credible interval indicating good performance of the models. Conclusion Methodology introduced here has the potential for efficient assessment of the contribution of malaria transmission in mortality and monitoring performance of control and intervention strategies.
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Affiliation(s)
- Susan Fred Rumisha
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; Department Biozentrum, University of Basel, Basel, Switzerland; Department of Disease Surveillance and Geographical Information Systems, National Institute for Medical Research, Dar es Salaam, Tanzania
| | - Thomas Smith
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; Department Biozentrum, University of Basel, Basel, Switzerland
| | | | | | - Penelope Vounatsou
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; Department Biozentrum, University of Basel, Basel, Switzerland;
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Clements ACA, Reid HL, Kelly GC, Hay SI. Further shrinking the malaria map: how can geospatial science help to achieve malaria elimination? THE LANCET. INFECTIOUS DISEASES 2013; 13:709-18. [PMID: 23886334 DOI: 10.1016/s1473-3099(13)70140-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Malaria is one of the biggest contributors to deaths caused by infectious disease. More than 30 countries have planned or started programmes to target malaria elimination, often with explicit support from international donors. The spatial distribution of malaria, at all levels of endemicity, is heterogeneous. Moreover, populations living in low-endemic settings where elimination efforts might be targeted are often spatially heterogeneous. Geospatial methods, therefore, can help design, target, monitor, and assess malaria elimination programmes. Rapid advances in technology and analytical methods have allowed the spatial prediction of malaria risk and the development of spatial decision support systems, which can enhance elimination programmes by enabling accurate and timely resource allocation. However, no framework exists for assessment of geospatial instruments. Research is needed to identify measurable indicators of elimination progress and to quantify the effect of geospatial methods in achievement of elimination outcomes.
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Affiliation(s)
- Archie C A Clements
- University of Queensland, Infectious Disease Epidemiology Unit, School of Population Health, Herston, QLD, Australia.
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Yamana TK, Bomblies A, Laminou IM, Duchemin JB, Eltahir EAB. Linking environmental variability to village-scale malaria transmission using a simple immunity model. Parasit Vectors 2013; 6:226. [PMID: 23919581 PMCID: PMC3750354 DOI: 10.1186/1756-3305-6-226] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Accepted: 08/01/2013] [Indexed: 11/17/2022] Open
Abstract
Background Individuals continuously exposed to malaria gradually acquire immunity that protects from severe disease and high levels of parasitization. Acquired immunity has been incorporated into numerous models of malaria transmission of varying levels of complexity (e.g. Bull World Health Organ 50:347, 1974; Am J Trop Med Hyg 75:19, 2006; Math Biosci 90:385–396, 1988). Most such models require prescribing inputs of mosquito biting rates or other entomological or epidemiological information. Here, we present a model with a novel structure that uses environmental controls of mosquito population dynamics to simulate the mosquito biting rates, malaria prevalence as well as variability in protective immunity of the population. Methods A simple model of acquired immunity to malaria is presented and tested within the framework of the Hydrology, Entomology and Malaria Transmission Simulator (HYDREMATS), a coupled hydrology and agent-based entomology model. The combined model uses environmental data including rainfall, temperature, and topography to simulate malaria prevalence and level of acquired immunity in the human population. The model is used to demonstrate the effect of acquired immunity on malaria prevalence in two Niger villages that are hydrologically and entomologically very different. Simulations are conducted for the year 2006 and compared to malaria prevalence observations collected from the two villages. Results Blood smear samples from children show no clear difference in malaria prevalence between the two villages despite pronounced differences in observed mosquito abundance. The similarity in prevalence is attributed to the moderating effect of acquired immunity, which depends on prior exposure to the parasite through infectious bites - and thus the hydrologically determined mosquito abundance. Modelling the level of acquired immunity can affect village vulnerability to climatic anomalies. Conclusions The model presented has a novel structure constituting a mechanistic link between spatial and temporal environmental variability and village-scale malaria transmission. Incorporating acquired immunity into the model has allowed simulation of prevalence in the two villages, and isolation of the effects of acquired immunity in dampening the difference in prevalence between the two villages. Without these effects, the difference in prevalence between the two villages would have been significantly larger in response to the large differences in mosquito populations and the associated biting rates.
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Affiliation(s)
- Teresa K Yamana
- Massachusetts Institute of Technology, 15 Vassar Street, Cambridge, MA 02139, USA.
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Thomas CJ, Cross DE, Bøgh C. Landscape movements of Anopheles gambiae malaria vector mosquitoes in rural Gambia. PLoS One 2013; 8:e68679. [PMID: 23874719 PMCID: PMC3715529 DOI: 10.1371/journal.pone.0068679] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 06/04/2013] [Indexed: 12/03/2022] Open
Abstract
BACKGROUND For malaria control in Africa it is crucial to characterise the dispersal of its most efficient vector, Anopheles gambiae, in order to target interventions and assess their impact spatially. Our study is, we believe, the first to present a statistical model of dispersal probability against distance from breeding habitat to human settlements for this important disease vector. METHODS/PRINCIPAL FINDINGS We undertook post-hoc analyses of mosquito catches made in The Gambia to derive statistical dispersal functions for An. gambiae sensu lato collected in 48 villages at varying distances to alluvial larval habitat along the River Gambia. The proportion dispersing declined exponentially with distance, and we estimated that 90% of movements were within 1.7 km. Although a 'heavy-tailed' distribution is considered biologically more plausible due to active dispersal by mosquitoes seeking blood meals, there was no statistical basis for choosing it over a negative exponential distribution. Using a simple random walk model with daily survival and movements previously recorded in Burkina Faso, we were able to reproduce the dispersal probabilities observed in The Gambia. CONCLUSIONS/SIGNIFICANCE Our results provide an important quantification of the probability of An. gambiae s.l. dispersal in a rural African setting typical of many parts of the continent. However, dispersal will be landscape specific and in order to generalise to other spatial configurations of habitat and hosts it will be necessary to produce tractable models of mosquito movements for operational use. We show that simple random walk models have potential. Consequently, there is a pressing need for new empirical studies of An. gambiae survival and movements in different settings to drive this development.
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Affiliation(s)
- Christopher J Thomas
- Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, Wales, United Kingdom.
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N. Njar G, A. Akpama W, I. Iwara A, A. Ita E, Lasisi CJ. Mapping Risk Prone Zones of Malaria Vector Species in Cross River State, Nigeria. JOURNAL OF MEDICAL SCIENCES 2013. [DOI: 10.3923/jms.2013.76.85] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Satyanarayana B, Bhanderi P, Debry M, Maniatis D, Foré F, Badgie D, Jammeh K, Vanwing T, Farcy C, Koedam N, Dahdouh-Guebas F. A socio-ecological assessment aiming at improved forest resource management and sustainable ecotourism development in the mangroves of Tanbi Wetland National Park, The Gambia, West Africa. AMBIO 2012; 41:513-26. [PMID: 22351596 PMCID: PMC3390577 DOI: 10.1007/s13280-012-0248-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 10/20/2011] [Accepted: 01/12/2012] [Indexed: 05/15/2023]
Abstract
Although mangroves dominated by Avicennia germinans and Rhizophora mangle are extending over 6000 ha in the Tanbi Wetland National Park (TWNP) (The Gambia), their importance for local populations (both peri-urban and urban) is not well documented. For the first time, this study evaluates the different mangrove resources in and around Banjul (i.e., timber, non-timber, edible, and ethnomedicinal products) and their utilization patterns, including the possibility of ecotourism development. The questionnaire-based results have indicated that more than 80% of peri-urban population rely on mangroves for timber and non-timber products and consider them as very important for their livelihoods. However, at the same time, urban households demonstrate limited knowledge on mangrove species and their ecological/economic benefits. Among others, fishing (including the oyster-Crassostrea cf. gasar collection) and tourism are the major income-generating activities found in the TWNP. The age-old practices of agriculture in some parts of the TWNP are due to scarcity of land available for agriculture, increased family size, and alternative sources of income. The recent focus on ecotourism (i.e., boardwalk construction inside the mangroves near Banjul city) received a positive response from the local stakeholders (i.e., users, government, and non-government organizations), with their appropriate roles in sharing the revenue, rights, and responsibilities of this project. Though the guidelines for conservation and management of the TWNP seem to be compatible, the harmony between local people and sustainable resource utilization should be ascertained.
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Affiliation(s)
- Behara Satyanarayana
- Laboratory of Systems Ecology and Resource Management (Complexity and Dynamics of Tropical Systems), Département de Biologie des Organismes, Faculté des Sciences, Université Libre de Bruxelles—ULB, Avenue Franklin D. Roosevelt 50, 1050 Brussels, Belgium
- Laboratory of Plant Biology and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
- Institute of Oceanography, University Malaysia Terengganu—UMT, 21030 Kuala, Terengganu Malaysia
| | - Preetika Bhanderi
- Laboratory of Plant Biology and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
- African Conservation Centre, P.O. Box 15289-00509, Nairobi, Kenya
| | - Mélanie Debry
- Forest, Nature and Society Research Group, Université Catholique de Louvain—UCL, Louvain-la-Neuve, Belgium
| | - Danae Maniatis
- Laboratory of Plant Biology and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
- School of Geography and the Environment, Environmental Change Institute, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY UK
| | - Franka Foré
- Laboratory of Plant Biology and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
- Sociaal Culturele Agogiek, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
| | - Dawda Badgie
- National Environment Agency (NEA), Banjul, The Gambia
| | - Kawsu Jammeh
- Department of Parks & Wildlife Management, Abuko, The Gambia
| | - Tom Vanwing
- Sociaal Culturele Agogiek, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
| | - Christine Farcy
- Forest, Nature and Society Research Group, Université Catholique de Louvain—UCL, Louvain-la-Neuve, Belgium
| | - Nico Koedam
- Laboratory of Plant Biology and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
| | - Farid Dahdouh-Guebas
- Laboratory of Systems Ecology and Resource Management (Complexity and Dynamics of Tropical Systems), Département de Biologie des Organismes, Faculté des Sciences, Université Libre de Bruxelles—ULB, Avenue Franklin D. Roosevelt 50, 1050 Brussels, Belgium
- Laboratory of Plant Biology and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel—VUB, Pleinlaan 2, 1050 Brussels, Belgium
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Zhou SS, Zhang SS, Wang JJ, Zheng X, Huang F, Li WD, Xu X, Zhang HW. Spatial correlation between malaria cases and water-bodies in Anopheles sinensis dominated areas of Huang-Huai plain, China. Parasit Vectors 2012; 5:106. [PMID: 22650153 PMCID: PMC3414776 DOI: 10.1186/1756-3305-5-106] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Accepted: 05/31/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Malaria re-emerged in the Huang-Huai Plain of central China during 2006-2008, dominated with Anopheles sinensis as a vector. However, there is no information on strategies based on multi-factor analysis to effectively control the re-emergence of malaria in these areas. Previous experience indicates some relationship between the distribution of water bodies and malaria cases, but more detailed data are not available and in-depth studies have not been conducted up to now. The objective of this study was to identify the relationship between the distribution of water bodies and presentation of malaria cases using spatial analysis tools in order to provide guidance to help formulate effective strategies for use in controlling the sources of malaria infection, based on the identification of risk areas and population. METHODS The geographic information of malaria cases and their surrounding water bodies were collected from Suixi, Guoyang, Guzhen, Yingshang, Fengyang and Yongqiao County in Anhui province, Yongcheng and Tongbai County in Henan province. All malaria cases distributed in 113 villages in these 8 counties were collected from the China Information System for Disease Control and Prevention and confirmed by household investigation. Data on GIS and malaria cases were mapped and analyzed with the software of ArcGIS 9.2 to identify the spatial correlation between malaria cases and water bodies. The distance from households with malaria cases to the nearest water bodies was used to calculate the OR value by Chi-square test. The risk area was identified through the comparison of OR values in different distances. RESULTS 357 malaria cases and their GPS data as well as surrounding water bodies were collected and analyzed. 74% of malaria cases were located within the extent of 60 m proximity to the water bodies. The risk rate of people living there and presenting with malaria was significantly higher than others (OR = 1.6,95%CI (1.042, 2.463),P < 0.05). CONCLUSIONS The results revealed that distribution of water bodies is an important factor influencing the occurrence and distribution of malaria cases in the An.sinensis areas, and implies that the scope and population within 60 m around water bodies are at risk and could be a targeted population for case management of malaria.
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Affiliation(s)
- Shui-sen Zhou
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, No.207 Rui Jin Er Road, Shanghai, People’s Republic of China
| | - Shao-sen Zhang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, No.207 Rui Jin Er Road, Shanghai, People’s Republic of China
| | - Jian-jun Wang
- Anhui Province Center for Disease Control and Prevention, No.12560 Fanhua Road in Economic-Technological Development Zone, Hefei, People’s Republic of China
| | - Xiang Zheng
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, No.207 Rui Jin Er Road, Shanghai, People’s Republic of China
| | - Fang Huang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, No.207 Rui Jin Er Road, Shanghai, People’s Republic of China
| | - Wei-dong Li
- Anhui Province Center for Disease Control and Prevention, No.12560 Fanhua Road in Economic-Technological Development Zone, Hefei, People’s Republic of China
| | - Xian Xu
- Anhui Province Center for Disease Control and Prevention, No.12560 Fanhua Road in Economic-Technological Development Zone, Hefei, People’s Republic of China
| | - Hong-wei Zhang
- Henan Province Center for Disease Control and Prevention, Eastern Nongye Road, Zhengzhou, People’s Republic of China
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Dambach P, Machault V, Lacaux JP, Vignolles C, Sié A, Sauerborn R. Utilization of combined remote sensing techniques to detect environmental variables influencing malaria vector densities in rural West Africa. Int J Health Geogr 2012; 11:8. [PMID: 22443452 PMCID: PMC3331805 DOI: 10.1186/1476-072x-11-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2012] [Accepted: 03/23/2012] [Indexed: 11/10/2022] Open
Abstract
Introduction The use of remote sensing has found its way into the field of epidemiology within the last decades. With the increased sensor resolution of recent and future satellites new possibilities emerge for high resolution risk modeling and risk mapping. Methods A SPOT 5 satellite image, taken during the rainy season 2009 was used for calculating indices by combining the image's spectral bands. Besides the widely used Normalized Difference Vegetation Index (NDVI) other indices were tested for significant correlation against field observations. Multiple steps, including the detection of surface water, its breeding appropriateness for Anopheles and modeling of vector imagines abundance, were performed. Data collection on larvae, adult vectors and geographic parameters in the field, was amended by using remote sensing techniques to gather data on altitude (Digital Elevation Model = DEM), precipitation (Tropical Rainfall Measurement Mission = TRMM), land surface temperatures (LST). Results The DEM derived altitude as well as indices calculations combining the satellite's spectral bands (NDTI = Normalized Difference Turbidity Index, NDWI Mac Feeters = Normalized Difference Water Index) turned out to be reliable indicators for surface water in the local geographic setting. While Anopheles larvae abundance in habitats is driven by multiple, interconnected factors - amongst which the NDVI - and precipitation events, the presence of vector imagines was found to be correlated negatively to remotely sensed LST and positively to the cumulated amount of rainfall in the preceding 15 days and to the Normalized Difference Pond Index (NDPI) within the 500 m buffer zone around capture points. Conclusions Remotely sensed geographical and meteorological factors, including precipitations, temperature, as well as vegetation, humidity and land cover indicators could be used as explanatory variables for surface water presence, larval development and imagines densities. This modeling approach based on remotely sensed information is potentially useful for counter measures that are putting on at the environmental side, namely vector larvae control via larviciding and water body reforming.
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Affiliation(s)
- Peter Dambach
- Institute of Public Health, University of Heidelberg, Heidelberg, Germany.
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Badu K, Afrane YA, Larbi J, Stewart VA, Waitumbi J, Angov E, Ong'echa JM, Perkins DJ, Zhou G, Githeko A, Yan G. Marked variation in MSP-119 antibody responses to malaria in western Kenyan highlands. BMC Infect Dis 2012; 12:50. [PMID: 22380785 PMCID: PMC3306741 DOI: 10.1186/1471-2334-12-50] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Accepted: 03/01/2012] [Indexed: 11/25/2022] Open
Abstract
Background Assessment of malaria endemicity at different altitudes and transmission intensities, in the era of dwindling vector densities in the highlands, will provide valuable information for malaria control and surveillance. Measurement of serum anti-malarial antibodies is a useful marker of malaria exposure that indicates long-term transmission potential. We studied the serologic evidence of malaria endemicity at two highland sites along a transmission intensity cline. An improved understanding of the micro-geographic variation in malaria exposure in the highland ecosystems will be relevant in planning effective malaria control. Methods Total IgG levels to Plasmodium falciparum MSP-119 were measured in an age-stratified cohort (< 5, 5-14 and ≥ 15 years) in 795 participants from an uphill and valley bottom residents during low and high malaria transmission seasons. Antibody prevalence and level was compared between different localities. Regression analysis was performed to examine the association between antibody prevalence and parasite prevalence. Age-specific MSP-119 seroprevalence data was fitted to a simple reversible catalytic model to investigate the relationship between parasite exposure and age. Results Higher MSP-119 seroprevalence and density were observed in the valley residents than in the uphill dwellers. Adults (> 15 years) recorded high and stable immune response in spite of changing seasons. Lower responses were observed in children (≤ 15 years), which, fluctuated with changing seasons particularly in the valley residents. In the uphill population, annual seroconversion rate (SCR) was 8.3% and reversion rate was 3.0%, with seroprevalence reaching a plateau of 73.3% by age of 20. Contrary, in the valley bottom population, the annual SCR was 35.8% and the annual seroreversion rate was 3.5%, and seroprevalence in the population had reached 91.2% by age 10. Conclusion The study reveals the micro-geographic variation in malaria endemicity in the highland eco-system; this validates the usefulness of sero-epidemiological tools in assessing malaria endemicity in the era of decreasing sensitivity of conventional tools.
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Affiliation(s)
- Kingsley Badu
- Center for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
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Le Port A, Watier L, Cottrell G, Ouédraogo S, Dechavanne C, Pierrat C, Rachas A, Bouscaillou J, Bouraima A, Massougbodji A, Fayomi B, Thiébaut A, Chandre F, Migot-Nabias F, Martin-Prevel Y, Garcia A, Cot M. Infections in infants during the first 12 months of life: role of placental malaria and environmental factors. PLoS One 2011; 6:e27516. [PMID: 22096588 PMCID: PMC3214070 DOI: 10.1371/journal.pone.0027516] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Accepted: 10/18/2011] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The association between placental malaria (PM) and first peripheral parasitaemias in early infancy was assessed in Tori Bossito, a rural area of Benin with a careful attention on transmission factors at an individual level. METHODOLOGY Statistical analysis was performed on 550 infants followed weekly from birth to 12 months. Malaria transmission was assessed by anopheles human landing catches every 6 weeks in 36 sampling houses and season defined by rainfall. Each child was located by GPS and assigned to the closest anopheles sampling house. Data were analysed by survival Cox models, stratified on the possession of insecticide-treated mosquito nets (ITNs) at enrolment. PRINCIPAL FINDINGS Among infants sleeping in a house with an ITN, PM was found to be highly associated to first malaria infections, after adjusting on season, number of anopheles, antenatal care (ANC) visits and maternal severe anaemia. Infants born from a malaria infected placenta had a 2.13 fold increased risk to present a first malaria infection than those born from a non infected placenta ([1.24-3.67], p<0.01) when sleeping in a house with an ITN. The risk to present a first malaria infection was increased by 3.2 to 6.5, according to the level of anopheles exposure (moderate or high levels, compared to the absence of anopheles). CONCLUSIONS First malaria infections in early childhood can be attributed simultaneously to both PM and high levels of exposure to infected anopheles. Protective measures as Intermittent Preventive Treatment during pregnancy (IPTp) and ITNs, targeted on both mothers and infants should be reinforced, as well as the research on new drugs and insecticides. In parallel, investigations on placental malaria have to be strengthened to better understand the mechanisms involved, and thus to protect adequately the infants high risk group.
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Affiliation(s)
- Agnès Le Port
- UMR216 Mère et enfant face aux infections tropicales, Institut de Recherche pour le Développement, Paris, France.
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Harris C, Kihonda J, Lwetoijera D, Dongus S, Devine G, Majambere S. A simple and efficient tool for trapping gravid Anopheles at breeding sites. Parasit Vectors 2011; 4:125. [PMID: 21722391 PMCID: PMC3141746 DOI: 10.1186/1756-3305-4-125] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Accepted: 07/02/2011] [Indexed: 11/25/2022] Open
Abstract
Background No effective tool currently exists for trapping ovipositing malaria vectors. This creates a gap in our ability to investigate the behavior and ecology of gravid Anopheles. Findings Here we describe a simple trap that collects ovipositing Anopheline and Culicine mosquitoes. It consists of an acetate sheet coated in glue that floats on the water surface. Ten breeding sites were selected in rural Tanzania and 10 sticky traps set in each. These caught a total of 74 gravid Anopheles (54 An. arabiensis, 1 An. gambiae s.s. and 16 unamplified) and 1333 gravid Culicines, in just two trap nights. This simple sampling tool provides an opportunity to further our understanding of the behavior and ecology of gravid female Anophelines. It strongly implies that at least two of the major vectors of malaria in Africa land on the water surface during the oviposition process, and demonstrates that Anophelines and Culicines often share the same breeding sites. Conclusion This simple and efficient trap has clear potential for the study of oviposition site choice and productivity, gravid dispersal, and vector control techniques which use oviposition behavior as a means of disseminating larvicides.
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Affiliation(s)
- Caroline Harris
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
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Zhou SS, Huang F, Wang JJ, Zhang SS, Su YP, Tang LH. Geographical, meteorological and vectorial factors related to malaria re-emergence in Huang-Huai River of central China. Malar J 2010; 9:337. [PMID: 21092326 PMCID: PMC3003275 DOI: 10.1186/1475-2875-9-337] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Accepted: 11/24/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Malaria still represents a significant public health problem in China, and the cases dramatically increased in the areas along the Huang-Huai River of central China after 2001. Considering spatial aggregation of malaria cases and specific vectors, the geographical, meteorological and vectorial factors were analysed to determine the key factors related to malaria re-emergence in these particular areas. METHODS The geographic information of 357 malaria cases and 603 water bodies in 113 villages were collected to analyse the relationship between the residence of malaria cases and water body. Spearman rank correlation, multiple regression, curve fitting and trend analysis were used to explain the relationship between the meteorological factors and malaria incidence. Entomological investigation was conducted in two sites to get the vectorial capacity and the basic reproductive rate to determine whether the effect of vector lead to malaria re-emergence. RESULTS The distances from household of cases to the nearest water-body was positive-skew distributed, the median was 60.9 m and 74% malaria cases were inhabited in the extent of 60 m near the water body, and the risk rate of people live there attacked by malaria was higher than others(OR = 1.6, 95%CI (1.042, 2.463), P < 0.05). The annual average temperature and rainfall may have close relationship with annual incidence. The average monthly temperature and rainfall were the key factors, and the correlation coefficients are 0.501 and 0.304(P < 0.01), respectively. Moreover, 75.3% changes of monthly malaria incidence contributed to the average monthly temperature (T(mean)), the average temperature of last two months(T(mean₀₁)) and the average rainfall of current month (R(mean)) and the regression equation was Y = -2.085 + 0.839I₁ + 0.998T(mean₀) - 0.86T(mean₀₁) + 0.16R(mean₀). All the collected mosquitoes were Anopheles sinensis. The vectorial capacity and the basic reproductive rate of An. sinensis in two sites were 0.6969, 0.4983 and 2.1604, 1.5447, respectively. CONCLUSION The spatial distribution between malaria cases and water-body, the changing of meteorological factors, and increasing vectorial capacity and basic reproductive rate of An. sinensis leaded to malaria re-emergence in these areas.
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Affiliation(s)
- Shui S Zhou
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai 200025, PR China
| | - Fang Huang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai 200025, PR China
| | - Jian J Wang
- Department of Parasitology, Anhui Center for Disease Control and Prevention, Hefei 230061, PR China
| | - Shao S Zhang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai 200025, PR China
| | - Yun P Su
- Department of Parasitology, Henan Center for Disease Control and Prevention, Zhengzhou, 450003, PR China
| | - Lin H Tang
- National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention; WHO Collaborating Centre for Malaria, Schistosomiasis and Filariasis; Laboratory of Parasite and Vector Biology, Ministry of Health, Shanghai 200025, PR China
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Bejon P, Williams TN, Liljander A, Noor AM, Wambua J, Ogada E, Olotu A, Osier FHA, Hay SI, Färnert A, Marsh K. Stable and unstable malaria hotspots in longitudinal cohort studies in Kenya. PLoS Med 2010; 7:e1000304. [PMID: 20625549 PMCID: PMC2897769 DOI: 10.1371/journal.pmed.1000304] [Citation(s) in RCA: 197] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Accepted: 05/27/2010] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND Infectious diseases often demonstrate heterogeneity of transmission among host populations. This heterogeneity reduces the efficacy of control strategies, but also implies that focusing control strategies on "hotspots" of transmission could be highly effective. METHODS AND FINDINGS In order to identify hotspots of malaria transmission, we analysed longitudinal data on febrile malaria episodes, asymptomatic parasitaemia, and antibody titres over 12 y from 256 homesteads in three study areas in Kilifi District on the Kenyan coast. We examined heterogeneity by homestead, and identified groups of homesteads that formed hotspots using a spatial scan statistic. Two types of statistically significant hotspots were detected; stable hotspots of asymptomatic parasitaemia and unstable hotspots of febrile malaria. The stable hotspots were associated with higher average AMA-1 antibody titres than the unstable clusters (optical density [OD] = 1.24, 95% confidence interval [CI] 1.02-1.47 versus OD = 1.1, 95% CI 0.88-1.33) and lower mean ages of febrile malaria episodes (5.8 y, 95% CI 5.6-6.0 versus 5.91 y, 95% CI 5.7-6.1). A falling gradient of febrile malaria incidence was identified in the penumbrae of both hotspots. Hotspots were associated with AMA-1 titres, but not seroconversion rates. In order to target control measures, homesteads at risk of febrile malaria could be predicted by identifying the 20% of homesteads that experienced an episode of febrile malaria during one month in the dry season. That 20% subsequently experienced 65% of all febrile malaria episodes during the following year. A definition based on remote sensing data was 81% sensitive and 63% specific for the stable hotspots of asymptomatic malaria. CONCLUSIONS Hotspots of asymptomatic parasitaemia are stable over time, but hotspots of febrile malaria are unstable. This finding may be because immunity offsets the high rate of febrile malaria that might otherwise result in stable hotspots, whereas unstable hotspots necessarily affect a population with less prior exposure to malaria.
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Affiliation(s)
- Philip Bejon
- Kilifi KEMRI-Wellcome Trust Collaborative Research Programme, Centre for Geographic Medicine Research-Coast, Kilifi, Kenya.
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Dambach P, Sié A, Lacaux JP, Vignolles C, Machault V, Sauerborn R. Using high spatial resolution remote sensing for risk mapping of malaria occurrence in the Nouna district, Burkina Faso. Glob Health Action 2009; 2. [PMID: 20052428 PMCID: PMC2799258 DOI: 10.3402/gha.v2i0.2094] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 09/21/2009] [Accepted: 09/21/2009] [Indexed: 11/21/2022] Open
Abstract
Introduction Malaria control measures such as early diagnosis and treatment, intermittent treatment of pregnant women, impregnated bed nets, indoor spraying and larval control measures are difficult to target specifically because of imprecise estimates of risk at a small-scale level. Ways of estimating local risks for malaria are therefore important. Methods A high-resolution satellite view from the SPOT 5 satellite during 2008 was used to generate a land cover classification in the malaria endemic lowland of North-Western Burkina Faso. For the area of a complete satellite view of 60 × 60 km, a supervised land cover classification was carried out. Ten classes were built and correlated to land cover types known for acting as Anopheles mosquito breeding sites. Results According to known correlations of Anopheles larvae presence and surface water-related land cover, cultivated areas in the riverine vicinity of Kossi River were shown to be one of the most favourable sites for Anopheles production. Similar conditions prevail in the South of the study region, where clayey soils and higher precipitations benefit the occurrence of surface water. Besides pools, which are often directly detectable, rice fields and occasionally flooded crops represent most appropriate habitats. On the other hand, forests, elevated regions on porous soils, grasslands and the dryer, sandy soils in the north-western part turned out to deliver fewer mosquito breeding opportunities. Conclusions Potential high and low risks for malaria at the village level can be differentiated from satellite data. While much remains to be done in terms of establishing correlations between remotely sensed risks and malaria disease patterns, this is a potentially useful approach which could lead to more focused disease control programmes.
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Affiliation(s)
- Peter Dambach
- Department of Tropical Hygiene and Public Health, University of Heidelberg, Heidelberg, Germany
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Household and microeconomic factors associated with malaria in Mpumalanga, South Africa. Trans R Soc Trop Med Hyg 2009; 104:143-7. [PMID: 19732924 DOI: 10.1016/j.trstmh.2009.07.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2009] [Revised: 07/10/2009] [Accepted: 07/10/2009] [Indexed: 11/22/2022] Open
Abstract
A household matched case-control study design was used to explore associations between household characteristics and malaria risk in seven study towns in the hypoendemic area of Mpumalanga Province, South Africa. Controls were identified from neighboring households of each case. Principle component analysis was used to calculate a wealth index for households to allow comparison across socioeconomic groups. Conditional univariate and multiple logistic regression analyses were used to assess associations between household malaria risk and potential risk factors. Univariate analysis demonstrated an increased household malaria risk for people living in mud-walled houses compared with those in brick dwellings (OR=5.10, 95% CI 2.03-12.80, P=0.001). Multivariate analysis confirmed the association between malaria risk and mud-wall construction (OR=6.12, 95% CI 2.26-16.59, P=0.001) and demonstrated an association with opening windows after retiring to sleep (OR=4.01, 95% CI 1.32-12.18, P=0.014). An inverse association between household wealth, third (OR=0.24, 95% CI 0.09-0.65, P=0.005) and fourth quartiles (OR=0.27, 95% CI 0.10-0.79, P=0.016), and malaria risk was observed. Associations found here include increased household malaria risk and mud-wall construction, the practice of opening of windows at night and relative household poverty. Education campaigns targeting risk behavior may reduce malaria risk, but economic development is a more important intervention.
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Rincón-Romero ME, Londoño JE. Mapping malaria risk using environmental and anthropic variables. REVISTA BRASILEIRA DE EPIDEMIOLOGIA 2009. [DOI: 10.1590/s1415-790x2009000300005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Despite much research in the identification of areas with malaria, it is urgent to further investigate mapping techniques to achieve better approaches in strategies to prevent, mitigate, and eradicate the mosquito and the illness eventually. By using spatial distributed modeling techniques with Geographical Information Systems (GIS), the study proposes methodology to map malaria risk zoning for the municipality of Buenaventura in Colombia. The model proposed by Craig et al.¹ using climatic information was adapted to the conditions of the study area regarding scale and spatial resolution. Geomorphologic and anthropic variables were added to improve spatial allocation of areas with higher risk of contracting the illness, refining zoning. Then, they were contrasted with the locations reported by health entities², taking into account spatial distribution. The comparison of results shows a decrease in the area obtained initially using the Craig et al. model¹ (1999), from 5,422.4 km² (89.1% of the municipality's territory) to 624.3km² (approximately 10% of the municipality's area), yielding a total reduction of 78.8% when environmental and anthropic variables were included in the model. Data show that of the 9,863 cases reported during 2001 to 2005 for 20 selected towns as basis for the amount of surveyed malaria cases², 1,132 were located in the very high-risk areas, 7,662 were in the areas of moderate risk, and 1,066 cases in low-risk areas, showing that 89% of the cases reported fell into the areas with higher risk for malaria.
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Coleman M, Coleman M, Mabuza AM, Kok G, Coetzee M, Durrheim DN. Using the SaTScan method to detect local malaria clusters for guiding malaria control programmes. Malar J 2009; 8:68. [PMID: 19374738 PMCID: PMC2679049 DOI: 10.1186/1475-2875-8-68] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2008] [Accepted: 04/17/2009] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND Mpumalanga Province, South Africa is a low malaria transmission area that is subject to malaria epidemics. SaTScan methodology was used by the malaria control programme to detect local malaria clusters to assist disease control planning. The third season for case cluster identification overlapped with the first season of implementing an outbreak identification and response system in the area. METHODS SaTScan software using the Kulldorf method of retrospective space-time permutation and the Bernoulli purely spatial model was used to identify malaria clusters using definitively confirmed individual cases in seven towns over three malaria seasons. Following passive case reporting at health facilities during the 2002 to 2005 seasons, active case detection was carried out in the communities, this assisted with determining the probable source of infection. The distribution and statistical significance of the clusters were explored by means of Monte Carlo replication of data sets under the null hypothesis with replications greater than 999 to ensure adequate power for defining clusters. RESULTS AND DISCUSSION SaTScan detected five space-clusters and two space-time clusters during the study period. There was strong concordance between recognized local clustering of cases and outbreak declaration in specific towns. Both Albertsnek and Thambokulu reported malaria outbreaks in the same season as space-time clusters. This synergy may allow mutual validation of the two systems in confirming outbreaks demanding additional resources and cluster identification at local level to better target resources. CONCLUSION Exploring the clustering of cases assisted with the planning of public health activities, including mobilizing health workers and resources. Where appropriate additional indoor residual spraying, focal larviciding and health promotion activities, were all also carried out.
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Affiliation(s)
- Marlize Coleman
- School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
| | - Michael Coleman
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK
| | - Aaron M Mabuza
- Mpumalanga Department of Health, 66 Anderson Street, Nelspruit, 1200, South Africa
| | - Gerdalize Kok
- Mpumalanga Department of Health, 66 Anderson Street, Nelspruit, 1200, South Africa
| | - Maureen Coetzee
- Vector Control Reference Unit, National Institute for Communicable Diseases, National Health Laboratory Service, 1 Modderfontein Road, Sandringham, 2131 Johannesburg, South Africa
- SA Research Chair in Medical Entomology & Vector Control, School of Pathology, University of the Witwatersrand, Johannesburg, South Africa
| | - David N Durrheim
- Hunter New England Population Health and Hunter Medical Research Institute, Locked Bag 10, Wallsend, 2287, Australia
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Mutuku FM, Bayoh MN, Hightower AW, Vulule JM, Gimnig JE, Mueke JM, Amimo FA, Walker ED. A supervised land cover classification of a western Kenya lowland endemic for human malaria: associations of land cover with larval Anopheles habitats. Int J Health Geogr 2009; 8:19. [PMID: 19371425 PMCID: PMC2676261 DOI: 10.1186/1476-072x-8-19] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Accepted: 04/16/2009] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND A supervised land cover classification was developed from very high resolution IKONOS satellite data and extensive ground truth sampling of a ca. 10 sq km malaria-endemic lowland in western Kenya. The classification was then applied to an investigation of distribution of larval Anopheles habitats. The hypothesis was that the distribution and abundance of aquatic habitats of larvae of various species of mosquitoes in the genus Anopheles is associated with identifiable landscape features. RESULTS AND DISCUSSION The classification resulted in 7 distinguishable land cover types, each with a distinguishable vegetation pattern, was highly accurate (89%, Kappa statistic = 0.86), and had a low rate of omission and commission errors. A total of 1,198 habitats and 19,776 Anopheles larvae of 9 species were quantified in samples from a rainy season, and 184 habitats and 582 larvae from a dry season. Anopheles gambiae s.l. was the dominant species complex (51% of total) and A. arabiensis the dominant species. Agricultural land covers (mature maize fields, newly cultivated fields, and pastured grasslands) were positively associated with presence of larval habitats, and were located relatively close to stream channels; whilst nonagricultural land covers (short shrubs, medium shrubs, tall shrubs, and bare soil around residences) were negatively associated with presence of larval habitats and were more distant from stream channels. Number of larval habitats declined exponentially with distance from streams. IKONOS imagery was not useful in direct detection of larval habitats because they were small and turbid (resembling bare soil), but was useful in localization of them through statistical associations with specific land covers. CONCLUSION A supervised classification of land cover types in rural, lowland, western Kenya revealed a largely human-modified and fragmented landscape consisting of agricultural and domestic land uses. Within it, larval habitats of Anopheles vectors of human malaria were associated with certain land cover types, of largely agricultural origin, and close to streams. Knowledge of these associations can inform malaria control to gather information on potential larval habitats more efficiently than by field survey and can do so over large areas.
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Affiliation(s)
- FM Mutuku
- Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - MN Bayoh
- Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - AW Hightower
- Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya
| | - JM Vulule
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
| | - JE Gimnig
- Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA
| | - JM Mueke
- Department of Zoological Sciences, Kenyatta University, Nairobi, Kenya
| | - FA Amimo
- Department of Biology, University of Eastern Africa, Baraton, Kenya
| | - ED Walker
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, USA
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Yeshiwondim AK, Gopal S, Hailemariam AT, Dengela DO, Patel HP. Spatial analysis of malaria incidence at the village level in areas with unstable transmission in Ethiopia. Int J Health Geogr 2009; 8:5. [PMID: 19171051 PMCID: PMC2646707 DOI: 10.1186/1476-072x-8-5] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2008] [Accepted: 01/26/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Malaria is the leading cause of morbidity and mortality in Ethiopia, accounting for over five million cases and thousands of deaths annually. The risks of morbidity and mortality associated with malaria are characterized by spatial and temporal variation across the country. This study examines the spatial and temporal patterns of malaria transmission at the local level and implements a risk mapping tool to aid in monitoring and disease control activities. METHODS In this study, we examine the global and local patterns of malaria distribution in 543 villages in East Shoa, central Ethiopia using individual-level morbidity data collected from six laboratory and treatment centers between September 2002 and August 2006. RESULTS Statistical analysis of malaria incidence by sex, age, and village through time reveal the presence of significant spatio-temporal variations. Poisson regression analysis shows a decrease in malaria incidence with increasing age. A significant difference in the malaria incidence density ratio (IDRs) is detected in males but not in females. A significant decrease in the malaria IDRs with increasing age is captured by a quadratic model. Local spatial statistics reveals clustering or hot spots within a 5 and 10 km distance of most villages in the study area. In addition, there are temporal variations in malaria incidence. CONCLUSION Malaria incidence varies according to gender and age, with males age 5 and above showing a statistically higher incidence. Significant local clustering of malaria incidence occurs between pairs of villages within 1-10 km distance lags. Malaria incidence was higher in 2002-2003 than in other periods of observation. Malaria hot spots are displayed as risk maps that are useful for monitoring and spatial targeting of prevention and control measures against the disease.
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Affiliation(s)
- Asnakew K Yeshiwondim
- Boston University, Department of Geography and Environment, 675 Commonwealth Ave., Boston, MA 02215, USA
- Federal Ministry of Health, PO Box: 1234, Addis Ababa, Ethiopia
| | - Sucharita Gopal
- Boston University, Department of Geography and Environment, 675 Commonwealth Ave., Boston, MA 02215, USA
| | | | | | - Hrishikesh P Patel
- Boston University, Department of Geography and Environment, 675 Commonwealth Ave., Boston, MA 02215, USA
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Jacob BG, Griffith D, Muturi E, Caamano EX, Shililu J, Githure JI, Novak RJ. Describing Anopheles arabiensis aquatic habitats in two riceland agro-ecosystems in Mwea, Kenya using a negative binomial regression model with a non-homogenous mean. Acta Trop 2009; 109:17-26. [PMID: 18930703 DOI: 10.1016/j.actatropica.2008.09.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2007] [Revised: 09/02/2008] [Accepted: 09/08/2008] [Indexed: 11/25/2022]
Abstract
This research illustrates a geostatistical approach for modeling the spatial distribution patterns of Anopheles arabiensis Patton (Patton) aquatic habitats in two riceland environments. QuickBird 0.61 m data, encompassing the visible bands and the near-infra-red (NIR) band, were selected to synthesize images of An. arabiensis aquatic habitats. These bands and field sampled data were used to determine ecological parameters associated with riceland larval habitat development. SAS was used to calculate univariate statistics, correlations and Poisson regression models. Global autocorrelation statistics were generated in ArcGISfrom georeferenced Anopheles aquatic habitats in the study sites. The geographic distribution of Anopheles gambiae s.l. aquatic habitats in the study sites exhibited weak positive autocorrelation; similar numbers of log-larval count habitats tend to clustered in space. Individual rice land habitat data were further evaluated in terms of their covariations with spatial autocorrelation, by regressing them on candidate spatial filter eigenvectors. Each eigenvector generated from a geographically weighted matrix, for both study sites, revealed a distinctive spatial pattern. The spatial autocorrelation components suggest the presence of roughly 14-30% redundant information in the aquatic habitat larval count samples. Synthetic map pattern variables furnish a method of capturing spatial dependency effects in the mean response term in regression analyses of rice land An. arabiensis aquatic habitat data.
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Risk factors for house-entry by culicine mosquitoes in a rural town and satellite villages in The Gambia. Parasit Vectors 2008; 1:41. [PMID: 18939969 PMCID: PMC2584634 DOI: 10.1186/1756-3305-1-41] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Accepted: 10/21/2008] [Indexed: 12/04/2022] Open
Abstract
Background Screening doors, windows and eaves of houses should reduce house entry by eusynanthropic insects, including the common African house mosquito Culex pipiens quinquefasciatus and other culicines. In the pre-intervention year of a randomized controlled trial investigating the protective effects of house screening against mosquito house entry, a multi-factorial risk factor analysis study was used to identify factors influencing house entry by culicines of nuisance biting and medical importance. These factors were house location, architecture, human occupancy and their mosquito control activities, and the number and type of domestic animals within the compound. Results 40,407 culicines were caught; the dominant species were Culex thalassius, Cx. pipiens s.l., Mansonia africanus, M. uniformis and Aedes aegypti. There were four times more Cx. pipiens s.l. in Farafenni town (geometric mean/trap/night = 8.1, 95% confidence intervals, CIs = 7.2–9.1) than in surrounding villages (2.1, 1.9–2.3), but over five times more other culicines in the villages (25.1, 22.1–28.7) than in town (4.6, 4.2–5.2). The presence of Cx. pipiens s.l. was reduced in both settings if the house had closed eaves (odds ratios, OR town = 0.62, 95% CIs = 0.49–0.77; OR village = 0.49, 0.33–0.73), but increased per additional person in the trapping room (OR town = 1.16, 1.09–1.24; OR village = 1.10, 1.02–1.18). In the town only, Cx. pipiens s.l. numbers were reduced if houses had a thatched roof (OR = 0.70, 0.51–0.96), for each additional cow tethered near the house (OR = 0.73, 0.65–0.82) and with increasing distance from a pit latrine (OR = 0.97, 0.95–0.99). In the villages a reduction in Cx. pipiens s.l. numbers correlated with increased horses in the compound (OR = 0.90, 0.82–0.99). The presence of all other culicines was reduced in houses with closed eaves (both locations), with horses tethered outside (village only) and with increasing room height (town only), but increased with additional people in the trapping room and where cows were tethered outside (both locations). Conclusion The findings of this study advocate eave closure and pit latrine treatment in all locations, and zooprophylaxis using horses in rural areas, as simple control measures that could reduce the number of culicines found indoors.
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Sogoba N, Vounatsou P, Bagayoko MM, Doumbia S, Dolo G, Gosoniu L, Traoré SF, Smith TA, Touré YT. Spatial distribution of the chromosomal forms of anopheles gambiae in Mali. Malar J 2008; 7:205. [PMID: 18847463 PMCID: PMC2579919 DOI: 10.1186/1475-2875-7-205] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Accepted: 10/10/2008] [Indexed: 11/17/2022] Open
Abstract
Background Maps of the distribution of malaria vectors are useful tools for stratification of malaria risk and for selective vector control strategies. Although the distribution of members of the Anopheles gambiae complex is well documented in Africa, a continuous map of the spatial distribution of the chromosomal forms of An. gambiae s.s. is not yet available at country level to support control efforts. Methods Bayesian geostatistical methods were used to produce continuous maps of the spatial distribution of the chromosomal forms of An. gambiae s.s. (Mopti, Bamako, Savanna and their hybrids/recombinants) based on their relative frequencies in relation to climatic and environmental factors in Mali. Results The maps clearly show that each chromosomal form favours a particular defined eco-climatic zone. The Mopti form prefers the dryer northern Savanna and Sahel and the flooded/irrigated areas of the inner delta of the Niger River. The Savanna form favours the Sudan savanna areas, particularly the South and South-Eastern parts of the country (Kayes and Sikasso regions). The Bamako form has a strong preference for specific environmental conditions and it is confined to the Sudan savanna areas around urban Bamako and the Western part of Sikasso region. The hybrids/recombinants favour the Western part of the country (Kayes region) bordering the Republic of Guinea Conakry. Conclusion The maps provide valuable information for selective vector control in Mali (insecticide resistance management) and may serve as a decision support tool for the basis for future malaria control strategies including genetically manipulated mosquitoes.
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Affiliation(s)
- Nafomon Sogoba
- Malaria Research and Training Center, Faculté de Médecine, de Pharmacie et d'Ondoto-Stomatologie, Université de Bamako, BP, 1805, Bamako, Mali.
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Tran A, Ponçon N, Toty C, Linard C, Guis H, Ferré JB, Lo Seen D, Roger F, de la Rocque S, Fontenille D, Baldet T. Using remote sensing to map larval and adult populations of Anopheles hyrcanus (Diptera: Culicidae) a potential malaria vector in Southern France. Int J Health Geogr 2008; 7:9. [PMID: 18302749 PMCID: PMC2291038 DOI: 10.1186/1476-072x-7-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2007] [Accepted: 02/26/2008] [Indexed: 12/20/2022] Open
Abstract
Background Although malaria disappeared from southern France more than 60 years ago, suspicions of recent autochthonous transmission in the French Mediterranean coast support the idea that the area could still be subject to malaria transmission. The main potential vector of malaria in the Camargue area, the largest river delta in southern France, is the mosquito Anopheles hyrcanus (Diptera: Culicidae). In the context of recent climatic and landscape changes, the evaluation of the risk of emergence or re-emergence of such a major disease is of great importance in Europe. When assessing the risk of emergence of vector-borne diseases, it is crucial to be able to characterize the arthropod vector's spatial distribution. Given that remote sensing techniques can describe some of the environmental parameters which drive this distribution, satellite imagery or aerial photographs could be used for vector mapping. Results In this study, we propose a method to map larval and adult populations of An. hyrcanus based on environmental indices derived from high spatial resolution imagery. The analysis of the link between entomological field data on An. hyrcanus larvae and environmental indices (biotopes, distance to the nearest main productive breeding sites of this species i.e., rice fields) led to the definition of a larval index, defined as the probability of observing An. hyrcanus larvae in a given site at least once over a year. Independent accuracy assessments showed a good agreement between observed and predicted values (sensitivity and specificity of the logistic regression model being 0.76 and 0.78, respectively). An adult index was derived from the larval index by averaging the larval index within a buffer around the trap location. This index was highly correlated with observed adult abundance values (Pearson r = 0.97, p < 0.05). This allowed us to generate predictive maps of An. hyrcanus larval and adult populations from the landscape indices. Conclusion This work shows that it is possible to use high resolution satellite imagery to map malaria vector spatial distribution. It also confirms the potential of remote sensing to help target risk areas, and constitutes a first essential step in assessing the risk of re-emergence of malaria in southern France.
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Affiliation(s)
- Annelise Tran
- Territories, Environment, Remote Sensing and Spatial Information Joint Research Unit (UMR TETIS), Maison de la Télédétection, 500 rue J,-F, Breton, 34093 Montpellier Cedex 5, France.
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Kirby MJ, Green C, Milligan PM, Sismanidis C, Jasseh M, Conway DJ, Lindsay SW. Risk factors for house-entry by malaria vectors in a rural town and satellite villages in The Gambia. Malar J 2008; 7:2. [PMID: 18179686 PMCID: PMC2267476 DOI: 10.1186/1475-2875-7-2] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2007] [Accepted: 01/07/2008] [Indexed: 12/03/2022] Open
Abstract
Background In the pre-intervention year of a randomized controlled trial investigating the protective effects of house screening against malaria-transmitting vectors, a multi-factorial risk factor analysis study was used to identify factors that influence mosquito house entry. Methods Mosquitoes were sampled using CDC light traps in 976 houses, each on one night, in Farafenni town and surrounding villages during the malaria-transmission season in The Gambia. Catches from individual houses were both (a) left unadjusted and (b) adjusted relative to the number of mosquitoes caught in four sentinel houses that were operated nightly throughout the period, to allow for night-to-night variation. Houses were characterized by location, architecture, human occupancy and their mosquito control activities, and the number and type of domestic animals within the compound. Results 106,536 mosquitoes were caught, of which 55% were Anopheles gambiae sensu lato, the major malaria vectors in the region. There were seven fold higher numbers of An. gambiae s.l. in the villages (geometric mean per trap night = 43.7, 95% confidence intervals, CIs = 39.5–48.4) than in Farafenni town (6.3, 5.7–7.2) and significant variation between residential blocks (p < 0.001). A negative binomial multivariate model performed equally well using unadjusted or adjusted trap data. Using the unadjusted data the presence of nuisance mosquitoes was reduced if the house was located in the town (odds ratio, OR = 0.11, 95% CIs = 0.09–0.13), the eaves were closed (OR = 0.71, 0.60–0.85), a horse was tethered near the house (OR = 0.77, 0.73–0.82), and churai, a local incense, was burned in the room at night (OR = 0.56, 0.47–0.66). Mosquito numbers increased per additional person in the house (OR = 1.04, 1.02–1.06) or trapping room (OR = 1.19, 1.13–1.25) and when the walls were made of mud blocks compared with concrete (OR = 1.44, 1.10–1.87). Conclusion This study demonstrates that the risk of malaria transmission is greatest in rural areas, where large numbers of people sleep in houses made of mud blocks, where the eaves are open, horses are not tethered nearby and where churai is not burnt at night. These factors need to be considered in the design and analysis of intervention studies designed to reduce malaria transmission in The Gambia and other parts of sub-Saharan Africa.
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Affiliation(s)
- Matthew J Kirby
- School of Biological and Biomedical Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK.
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Killeen GF, Tami A, Kihonda J, Okumu FO, Kotas ME, Grundmann H, Kasigudi N, Ngonyani H, Mayagaya V, Nathan R, Abdulla S, Charlwood JD, Smith TA, Lengeler C. Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania. BMC Infect Dis 2007; 7:121. [PMID: 17961211 PMCID: PMC2211306 DOI: 10.1186/1471-2334-7-121] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2007] [Accepted: 10/25/2007] [Indexed: 12/01/2022] Open
Abstract
Background Cost-sharing schemes incorporating modest targeted subsidies have promoted insecticide-treated nets (ITNs) for malaria prevention in the Kilombero Valley, southern Tanzania, since 1996. Here we evaluate resulting changes in bednet coverage and malaria transmission. Methods Bednets were sold through local agents at fixed prices representing a 34% subsidy relative to full delivery cost. A further targeted subsidy of 15% was provided to vulnerable groups through discount vouchers delivered through antenatal clinics and regular immunizations. Continuous entomological surveys (2,376 trap nights) were conducted from October 2001 to September 2003 in 25 randomly-selected population clusters of a demographic surveillance system which monitored net coverage. Results Mean net usage of 75% (11,982/16,086) across all age groups was achieved but now-obsolete technologies available at the time resulted in low insecticide treatment rates. Malaria transmission remained intense but was substantially reduced: Compared with an exceptionally high historical mean EIR of 1481, even non-users of nets were protected (EIR [fold reduction] = 349 infectious bites per person per year [×4]), while the average resident (244 [×6]), users of typical nets (210 [×7]) and users of insecticidal nets (105 [×14]) enjoyed increasing benefits. Conclusion Despite low net treatment levels, community-level protection was equivalent to the personal protection of an ITN. Greater gains for net users and non-users are predicted if more expensive long-lasting ITN technologies can be similarly promoted with correspondingly augmented subsidies. Cost sharing strategies represent an important option for national programmes lacking adequate financing to fully subsidize comprehensive ITN coverage.
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Affiliation(s)
- G F Killeen
- Ifakara Health Research and Development Centre, Box 53, Ifakara, Morogoro, United Republic of Tanzania.
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Deressa W, Ali A, Berhane Y. Household and socioeconomic factors associated with childhood febrile illnesses and treatment seeking behaviour in an area of epidemic malaria in rural Ethiopia. Trans R Soc Trop Med Hyg 2007; 101:939-47. [PMID: 17602716 DOI: 10.1016/j.trstmh.2007.04.018] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Revised: 04/23/2007] [Accepted: 04/23/2007] [Indexed: 11/21/2022] Open
Abstract
To assess household and socioeconomic factors associated with childhood febrile illnesses and treatment seeking behaviour, a study was conducted in Adami Tulu district in Ethiopia during the peak malaria transmission season in 2003. All mothers/caretakers of children <5 years of age were interviewed regarding their household characteristics, history of febrile illness (malaria) among children and actions taken 2 weeks prior to the survey. Of 3873 children, 21% had experienced fever in the past 2 weeks. Household ownership of a mosquito net (odds ratio (OR)=0.4, 95% CI 0.3-0.7) and prior spraying of the house with aerosols (OR=0.7, 95% CI 0.5-0.9) or DDT (OR=0.8, 95% CI 0.6-0.9) were associated with lower risk of febrile illnesses, whilst sharing the house with livestock increased the risk (OR=1.3, 95% CI 1.1-1.6). Treatment was sought for 87% of febrile children, with public facilities, private clinics and community health workers accessed fairly equally (26-27%). Home management was uncommon (6.4%). More febrile children from households in the middle (37.1%) and highest (44.6%) wealth categories sought treatment within 24h compared with the lowest category (18.3%). Widescale use of vector control measures such as mosquito nets and insecticide spraying of houses can effectively reduce the incidence of febrile illnesses among children.
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Affiliation(s)
- Wakgari Deressa
- Department of Community Health, Faculty of Medicine, Addis Ababa University, P.O. Box 9086, Addis Ababa, Ethiopia.
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Wilson S, Booth M, Jones FM, Mwatha JK, Kimani G, Kariuki HC, Vennervald BJ, Ouma JH, Muchiri E, Dunne DW. Age-adjusted Plasmodium falciparum antibody levels in school-aged children are a stable marker of microgeographical variations in exposure to Plasmodium infection. BMC Infect Dis 2007; 7:67. [PMID: 17603885 PMCID: PMC1947991 DOI: 10.1186/1471-2334-7-67] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2007] [Accepted: 06/29/2007] [Indexed: 11/10/2022] Open
Abstract
Background Amongst school-aged children living in malaria endemic areas, chronic morbidity and exacerbation of morbidity associated with other infections are often not coincident with the presence or levels of Plasmodium parasitaemia, but may result from long-term exposure to the parasite. Studies of hepatosplenomegaly associated with Schistosoma mansoni infection and exposure to Plasmodium infection indicate that differences that occur over 1–2 km in levels of Plasmodium transmission are related to the degree of exacerbation of hepatosplenomegaly and that Plasmodium falciparum schizont antigen (Pfs)-IgG3 levels may be a marker for the differing levels of exposure. Methods To investigate the validity of Pfs-IgG3 measurements as a tool to assess these comparative exposure levels on a microgeographical scale, cross-sectional community surveys were conducted over a 10 × 6 km study site in Makueni District, Kenya, during low and high malaria transmission seasons. During both high and low malaria transmission seasons, thick blood smears were examined microscopically and circulating Pfs-IgG3 levels measured from dried blood spot elute. GIS techniques were used to map prevalence of parasitaemia and Pfs-IgG3 levels. Results Microgeographical variations in prevalence of parasitaemia were observed during the high but not the low transmission season. Pfs-IgG3 levels were stable between high and low transmission seasons, but increased with age throughout childhood before reaching a plateau in adults. Adjusting Pfs-IgG3 levels of school-aged children for age prior to mapping resulted in spatial patterns that reflected the microgeographical variations observed for high season prevalence of parasitaemia, however, Pfs-IgG3 levels of adults did not. The distances over which age-adjusted Pfs-IgG3 of school-aged children fluctuated were comparable with those distances over which chronic morbidity has previous been shown to vary. Conclusion Age-adjusted Pfs-IgG3 levels of school-aged children are stable and when mapped can provide a tool sensitive enough to detect microgeographical variations in malaria exposure, that would be useful for studying the aetiology of morbidities associated with long-term exposure and co-infections.
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Affiliation(s)
- Shona Wilson
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Mark Booth
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Frances M Jones
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | | | | | - H Curtis Kariuki
- Division of Vector Borne Diseases, Kenyan Ministry of Health, PO Box 54840, Nairobi, Kenya
| | - Birgitte J Vennervald
- DBL – Institute for Health Research and Development, Jægersborg Alle 1D, 2920 Charlottenlund, Denmark
| | | | - Eric Muchiri
- Division of Vector Borne Diseases, Kenyan Ministry of Health, PO Box 54840, Nairobi, Kenya
| | - David W Dunne
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
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Abstract
BACKGROUND Mosquito larval control may prove to be an effective tool for incorporating into integrated vector management (IVM) strategies for reducing malaria transmission. Here the efficacy of microbial larvicides against Anopheles gambiae s.l. was tested in preparation for a large-scale larviciding programme in The Gambia. METHODS The impact of water-dispersible (WDG) and corn granule (CG) formulations of commercial Bacillus sphaericus strain 2362 (Bs; VectoLex) and Bacillus thuringiensis var.israelensis strain AM65-52 (Bti; VectoBac) on larval development were tested under laboratory and field conditions to (1) identify the susceptibility of local vectors, (2) evaluate the residual effect and re-treatment intervals, (3) test the effectiveness of the microbials under operational application conditions and (4) develop a method for large-scale application. RESULTS The major malaria vectors were highly susceptible to both microbials. The lethal concentration (LC) to kill 95% of third instar larvae of Anopheles gambiae s.s. after 24 hours was 0.023 mg/l (14.9 BsITU/l) for Bs WDG and 0.132 mg/l (396 ITU/l) for Bti WDG. In general Bs had little residual effect under field conditions even when the application rate was 200 times greater than the LC95. However, there was a residual effect up to 10 days in standardized field tests implemented during the dry season. Both microbials achieved 100% mortality of larvae 24-48 hours post-application but late instar larvae were detected 4 days after treatment. Pupae development was reduced by 94% (95% Confidence Interval = 90.8-97.5%) at weekly re-treatment intervals. Field tests showed that Bs had no residual activity against anopheline larvae. Both microbials provided complete protection when applied weekly. The basic training of personnel in identification of habitats, calibration of application equipment and active larviciding proved to be successful and achieved full coverage and control of mosquito larvae for three months under fully operational conditions. CONCLUSION Environmentally safe microbial larvicides can significantly reduce larval abundance in the natural habitats of The Gambia and could be a useful tool for inclusion in an IVM programme. The costs of the intervention in this setting could be reduced with formulations that provide a greater residual effect.
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Vanwambeke SO, Somboon P, Harbach RE, Isenstadt M, Lambin EF, Walton C, Butlin RK. Landscape and land cover factors influence the presence of Aedes and Anopheles larvae. JOURNAL OF MEDICAL ENTOMOLOGY 2007; 44:133-44. [PMID: 17294931 DOI: 10.1603/0022-2585(2007)44[133:lalcfi]2.0.co;2] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The objective of this study was to test for associations between land cover data and the presence of mosquito larvae of the genera Aedes Meigen and Anopheles Meigen in northern Thailand at the landscape scale. These associations were compared with associations between larval habitat variables and the presence of mosquito larvae at a finer spatial scale. Collection data for the larvae of one Aedes species and three species-groups of Anopheles, all of which are involved in pathogen transmission, were used. A variety of northern Thai landscapes were included, such as upland villages, lowland villages and peri-urban areas. Logistic regression was used to evaluate associations. Generally, land cover and landscape variables explained the presence of larvae as well as did larval habitat variables. Results were best for species/species-groups with specific habitat requirements. Land cover variables act as proxies for the types of habitat available and their attributes. Good knowledge of the habitat requirements of the immature stages of mosquitoes is necessary for interpreting the effects of land cover.
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Affiliation(s)
- Sophie O Vanwambeke
- Department of Geography, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
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