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Kamau WW, Sang R, Rotich G, Agha SB, Menza N, Torto B, Tchouassi DP. Patterns of Aedes aegypti abundance, survival, human-blood feeding and relationship with dengue risk, Kenya. FRONTIERS IN TROPICAL DISEASES 2023. [DOI: 10.3389/fitd.2023.1113531] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
Dengue virus (DENV) transmission risk is influenced by the bionomic traits of the key vector, Aedes aegypti. We investigated patterns of abundance, survival, and human blood-feeding of Ae. aegypti populations in two environments in Kenya: peri-urban Rabai (coastal Region, dengue-endemic) and rural Kerio Valley (Rift Valley Region, no reported dengue outbreak). In both environments, Ae. aegypti survival (estimated by parity), was inversely correlated with vector abundance, and this was influenced by weather conditions, notably temperature and relative humidity. In Rabai, Ae. aegypti mostly fed on humans (human blood index=51%), a pattern that corroborates with dengue cases in the coastal region. Aedes aegypti additionally, exhibited opportunistic feeding (livestock, rodents, reptiles, birds), suggesting the risk of human exposure to zoonotic pathogens via spillover transmission events aided by the vector. Abundance and human blood-feeding rates were consistently lower in Kerio Valley likely related to the degree of urbanization. Remarkably, the periods of high human feeding in Rabai coincided with high vector survival rates, a trend that could potentially drive intense DENV transmission at certain times of the year. We found a genetic influence of Ae. aegypti on the degree of anthropophagy but this could be influenced by potential seasonal shifts in human feeding. The findings of this study have implications both for DENV transmission risk and vector control strategies, but also in modeling which should integrate vector bionomic factors beyond vector abundance.
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Ompad DC, Kessler A, Van Eijk AM, Padhan TK, Haque MA, Sullivan SA, Tozan Y, Rocklöv J, Mohanty S, Pradhan MM, Sahu PK, Carlton JM. The effectiveness of malaria camps as part of the Durgama Anchalare Malaria Nirakaran (DAMaN) program in Odisha, India: study protocol for a cluster-assigned quasi-experimental study. Glob Health Action 2021; 14:1886458. [PMID: 33866961 PMCID: PMC8183513 DOI: 10.1080/16549716.2021.1886458] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Indian state of Odisha has a longstanding battle with forest malaria. Many remote and rural villages have poor access to health care, a problem that is exacerbated during the rainy season when malaria transmission is at its peak. Approximately 62% of the rural population consists of tribal groups who are among the communities most negatively impacted by malaria. To address the persistently high rates of malaria in these remote regions, the Odisha State Malaria Control Program introduced 'malaria camps' in 2017 where teams of health workers visit villages to educate the population, enhance vector control methods, and perform village-wide screening and treatment. Malaria rates declined statewide, particularly in forested areas, following the introduction of the malaria camps, but the impact of the intervention is yet to be externally evaluated. This study protocol describes a cluster-assigned quasi-experimental stepped-wedge study with a pretest-posttest control group design that evaluates if malaria camps reduce the prevalence of malaria, compared to control villages which receive the usual malaria control interventions (e.g. IRS, ITNs), as detected by PCR.
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Affiliation(s)
- Danielle C. Ompad
- School of Global Public Health, New York University, New York, NY, USA,CONTACT Danielle C. Ompad NYU School of Global Public Health, 715 Broadway, Room 1011, New York, NY10003USA
| | - Anne Kessler
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, NY, USA
| | - Anna Maria Van Eijk
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, NY, USA
| | - Timir K. Padhan
- Department of Molecular & Infectious Diseases, Community Welfare Society Hospital, Rourkela, Odisha, India
| | - Mohammed A. Haque
- Department of Molecular & Infectious Diseases, Community Welfare Society Hospital, Rourkela, Odisha, India
| | - Steven A. Sullivan
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, NY, USA
| | - Yesim Tozan
- School of Global Public Health, New York University, New York, NY, USA
| | - Joacim Rocklöv
- Department of Public Health and Clinical Medicine, Umea University, Umea, Sweden
| | - Sanjib Mohanty
- Department of Molecular & Infectious Diseases, Community Welfare Society Hospital, Rourkela, Odisha, India
| | - Madan M. Pradhan
- Department of Health & Family Welfare, State Vector Borne Disease Control Programme, Bhubaneswar, Odisha, India
| | - Praveen K. Sahu
- Department of Molecular & Infectious Diseases, Community Welfare Society Hospital, Rourkela, Odisha, India
| | - Jane M. Carlton
- School of Global Public Health, New York University, New York, NY, USA,Center for Genomics and Systems Biology, Department of Biology, New York University, New York, NY, USA
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Foley DH, Wilkerson RC, Kim HC, Klein TA, Kim MS, Li C, Levin DM, Rueda LM. Wing size and parity as markers of cohort demography for potential Anopheles (Culicidae: Diptera) malaria vectors in the Republic of Korea. JOURNAL OF VECTOR ECOLOGY : JOURNAL OF THE SOCIETY FOR VECTOR ECOLOGY 2020; 45:366-379. [PMID: 33207064 DOI: 10.1111/jvec.12406] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 09/15/2020] [Indexed: 06/11/2023]
Abstract
Wing lengths of parous (P) and nulliparous (NP) PCR-identified female Anopheles belenrae, An. kleini, An. pullus, and An. sinensis were determined from weekly trap collections at Camp Humphreys (CH), Ganghwa Island (GH), and Warrior Base (WB), Republic of Korea (ROK) during Jun-Oct, 2009. Wing length was greatest at the beginning and end of the study period. Wing length of NPs tended to be less than that of Ps before the period of maximum greening (Jul-Aug) but greater thereafter. Larger specimens tended to be Ps, and weekly wing length of Ps appeared less variable than NPs, possibly due to selection. A bimodal wing length frequency distribution of An. sinensis suggested two forms comprising small- (≤4.5 mm, SW) and large-winged females (>4.5 mm, LW). LW comprised the majority of peaks in abundance, however %SW, while still a minority, often increased during these times suggesting a density-dependent effect. At WB and GH, a two to three-week periodicity in %SW was obvious for An. sinensis and An. kleini. Analyses of weather station and satellite data showed that smaller-winged An. sinensis were associated with warmer, more humid, and greener times of the year. SW and LW specimens possibly result from agricultural practices that are common across large areas; regular synchronous peaks of SW and LW were observed from different sites. Peaks in SW Ps followed peaks in NPs in a 'ripple effect' one to two weeks apart, suggesting that wing length combined with parity could be used to follow the emergence and survival of mosquito cohorts.
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Affiliation(s)
- Desmond H Foley
- Walter Reed Biosystematics Unit, Department of Entomology, Walter Reed Army Institute of Research, Silver Spring, MD, 20910, U.S.A
- Entomology Department, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20013, U.S.A
| | - Richard C Wilkerson
- Walter Reed Biosystematics Unit, Department of Entomology, Walter Reed Army Institute of Research, Silver Spring, MD, 20910, U.S.A
- Entomology Department, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20013, U.S.A
| | - Heung Chul Kim
- Force Health Protection and Preventive Medicine, US Army Medical Activity-Korea, 65th Medical Brigade, Unit #15281, APO AP 96271-5281
| | - Terry A Klein
- Force Health Protection and Preventive Medicine, US Army Medical Activity-Korea, 65th Medical Brigade, Unit #15281, APO AP 96271-5281
| | - Myung-Soon Kim
- Force Health Protection and Preventive Medicine, US Army Medical Activity-Korea, 65th Medical Brigade, Unit #15281, APO AP 96271-5281
| | - Cong Li
- Walter Reed Biosystematics Unit, Department of Entomology, Walter Reed Army Institute of Research, Silver Spring, MD, 20910, U.S.A
| | - David M Levin
- Walter Reed Biosystematics Unit, Department of Entomology, Walter Reed Army Institute of Research, Silver Spring, MD, 20910, U.S.A
| | - Leopoldo M Rueda
- Walter Reed Biosystematics Unit, Department of Entomology, Walter Reed Army Institute of Research, Silver Spring, MD, 20910, U.S.A
- Entomology Department, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20013, U.S.A
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Ataguba JE. Socio-economic inequality in health service utilisation: Does accounting for seasonality in health-seeking behaviour matter? HEALTH ECONOMICS 2019; 28:1370-1376. [PMID: 31264315 PMCID: PMC6900122 DOI: 10.1002/hec.3925] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 05/09/2019] [Accepted: 05/31/2019] [Indexed: 05/31/2023]
Abstract
Seasonal variation exists in disease incidence. The variation could occur across the different regions in a country. This paper argues that using national household data that are not adjusted for seasonal and regional variations in disease incidence may not be directly suitable for assessing socio-economic inequality in annual outpatient service utilisation, including for cross-country comparison. In fact, annual health service utilisation may be understated or overstated depending on the period of data collection. This may lead to miss-estimation of socio-economic inequality in health service utilisation depending, among other things, on how health service utilisation, across geographical areas, varies by socio-economic status. Using a nationally representative dataset from South Africa, the paper applies a seasonality index that is constructed from the District Health Information System, an administrative dataset, to annualise public outpatient health service visits. Using the concentration index, socio-economic inequality in health service visits, after accounting for seasonal variations, was compared with that when seasonal variations are ignored. It was found that, in some cases, socio-economic inequality in outpatient health service visits depends on the socio-economic distribution of the seasonality index. This may justify the need to account for seasonal and geographical variations.
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Affiliation(s)
- John E. Ataguba
- Health Economics Unit, School of Public Health and Family Medicine, Health Sciences FacultyUniversity of Cape TownCape TownSouth Africa
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Mburu MM, Zembere K, Hiscox A, Banda J, Phiri KS, van den Berg H, Mzilahowa T, Takken W, McCann RS. Assessment of the Suna trap for sampling mosquitoes indoors and outdoors. Malar J 2019; 18:51. [PMID: 30795766 PMCID: PMC6387520 DOI: 10.1186/s12936-019-2680-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2018] [Accepted: 02/14/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Entomological monitoring is important for public health because it provides data on the distribution, abundance and host-seeking behaviour of disease vectors. Various methods for sampling mosquitoes exist, most of which are biased towards, or specifically target, certain portions of a mosquito population. This study assessed the Suna trap, an odour-baited trap for sampling host-seeking mosquitoes both indoors and outdoors. METHODS Two separate field experiments were conducted in villages in southern Malawi. The efficiency of the Suna trap in sampling mosquitoes was compared to that of the human landing catch (HLC) indoors and outdoors and the Centers for Disease, Control and Prevention Light Trap (CDC-LT) indoors. Potential competition between two Suna traps during simultaneous use of the traps indoors and outdoors was assessed by comparing mosquito catch sizes across three treatments: one trap indoors only; one trap outdoors only; and one trap indoors and one trap outdoors used simultaneously at the same house. RESULTS The efficiency of the Suna trap in sampling female anophelines was similar to that of HLC indoors (P = 0.271) and HLC outdoors (P = 0.125), but lower than that of CDC-LT indoors (P = 0.001). Anopheline catch sizes in the Suna trap used alone indoors were similar to indoor Suna trap catch sizes when another Suna trap was simultaneously present outdoors (P = 0.891). Similarly, catch sizes of female anophelines with the Suna trap outdoors were similar to those that were caught outdoors when another Suna trap was simultaneously present indoors (P = 0.731). CONCLUSIONS The efficiency of the Suna trap in sampling mosquitoes was equivalent to that of the HLC. Whereas the CDC-LT was more efficient in collecting female anophelines indoors, the use of this trap outdoors is limited given the requirement of setting it next to an occupied bed net. As demonstrated in this research, outdoor collections are also essential because they provide data on the relative contribution of outdoor biting to malaria transmission. Therefore, the Suna trap could serve as an alternative to the HLC and the CDC-LT, because it does not require the use of humans as natural baits, allows standardised sampling conditions across sampling points, and can be used outdoors. Furthermore, using two Suna traps simultaneously indoors and outdoors does not interfere with the sampling efficiency of either trap, which would save a considerable amount of time, energy, and resources compared to setting the traps indoors and then outdoors in two consecutive nights.
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Affiliation(s)
- Monicah M Mburu
- College of Medicine, University of Malawi, Blantyre, Malawi. .,Laboratory of Entomology, Wageningen University and Research, Wageningen, The Netherlands.
| | | | - Alexandra Hiscox
- Laboratory of Entomology, Wageningen University and Research, Wageningen, The Netherlands
| | - Jomo Banda
- College of Medicine, University of Malawi, Blantyre, Malawi.,MAC Communicable Diseases Action Centre, Blantyre, Malawi
| | - Kamija S Phiri
- College of Medicine, University of Malawi, Blantyre, Malawi
| | - Henk van den Berg
- Laboratory of Entomology, Wageningen University and Research, Wageningen, The Netherlands
| | - Themba Mzilahowa
- College of Medicine, University of Malawi, Blantyre, Malawi.,MAC Communicable Diseases Action Centre, Blantyre, Malawi
| | - Willem Takken
- Laboratory of Entomology, Wageningen University and Research, Wageningen, The Netherlands
| | - Robert S McCann
- College of Medicine, University of Malawi, Blantyre, Malawi.,Laboratory of Entomology, Wageningen University and Research, Wageningen, The Netherlands
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Foley DH, Klein TA, Kim HC, Kim MS, Wilkerson RC, Li C, Harrison G, Rueda LM. Seasonal dynamics of Anopheles species at three locations in the Republic of Korea. JOURNAL OF VECTOR ECOLOGY : JOURNAL OF THE SOCIETY FOR VECTOR ECOLOGY 2017; 42:335-348. [PMID: 29125241 DOI: 10.1111/jvec.12274] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 09/11/2017] [Indexed: 06/07/2023]
Abstract
Weekly changes in adult Anopheles species were monitored at Camp Humphreys (CH), Ganghwa Island (GH), and Warrior Base (WB), from May-October, 2009-2010 to explore the relationship between Plasmodium vivax development and vector dynamics in the Republic of Korea (ROK). Adult females were trapped and dissected to determine parity for estimating longevity, mortality, and birthrate. A degree-day (DD) method was used to estimate the extrinsic incubation period (EIP) of P. vivax and duration of the gonotrophic cycle and other life stages. Anopheles sinensis was the predominant species, with satellite data showing peak abundance occurring after the period of maximum greenness. Abundance peaks were location dependent, comprised nulliparous and parous females, and timing could not be fully explained by DD estimation. Parity showed synchronicity between locations and years and was highest for September and lowest during maximum greenness. Mosquito longevity was predicted to exceed the EIP (when malaria transmission is possible) during weeks 29, 31, 34, and near the end of the season. Area-wide changes in parity suggest a common cause; information on local larval habitat and agricultural practices may explain location-specific effects. DD estimates of EIP and parity could be used to predict when conditions are suitable for P. vivax transmission.
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Affiliation(s)
- Desmond H Foley
- Division of Entomology, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, U.S.A
- Entomology Department, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, U.S.A
| | - Terry A Klein
- MEDDAC-Korea/65th Medical Brigade, Unit 15281, Box 754, APO AP 96205-5281, U.S.A
| | - Heung Chul Kim
- 5th Medical Detachment, 168th Multifunctional Medical Battalion, 65th Medical Brigade, Unit 15247, APO AP 96205-5247, U.S.A
| | - Myung-Soon Kim
- 5th Medical Detachment, 168th Multifunctional Medical Battalion, 65th Medical Brigade, Unit 15247, APO AP 96205-5247, U.S.A
| | - Richard C Wilkerson
- Division of Entomology, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, U.S.A
| | - Cong Li
- Division of Entomology, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, U.S.A
| | - Genelle Harrison
- Division of Entomology, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, U.S.A
| | - Leopoldo M Rueda
- Division of Entomology, Walter Reed Army Institute of Research, 503 Robert Grant Avenue, Silver Spring, MD 20910, U.S.A
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Ferreira CP, Lyra SP, Azevedo F, Greenhalgh D, Massad E. Modelling the impact of the long-term use of insecticide-treated bed nets on Anopheles mosquito biting time. Malar J 2017; 16:373. [PMID: 28915892 PMCID: PMC5602891 DOI: 10.1186/s12936-017-2014-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 09/04/2017] [Indexed: 11/24/2022] Open
Abstract
Background Evidence of changing in biting and resting behaviour of the main malaria vectors has been mounting up in recent years as a result of selective pressure by the widespread and long-term use of insecticide-treated bed nets (ITNs), and indoor residual spraying. The impact of resistance behaviour on malaria intervention efficacy has important implications for the epidemiology and malaria control programmes. In this context, a theoretical framework is presented to understand the mechanisms determining the evolution of feeding behaviour under the pressure of use of ITNs. Methods An agent-based stochastic model simulates the impact of insecticide-treated bed nets on mosquito fitness by reducing the biting rates, as well as increasing mortality rates. The model also incorporates a heritability function that provides the necessary genetic plasticity upon which natural selection would act to maximize the fitness under the pressure of the control strategy. Results The asymptotic equilibrium distribution of mosquito population versus biting time is shown for several daily uses of ITNs, and the expected disruptive selection on this mosquito trait is observed in the simulations. The relative fitness of strains that bite at much earlier time with respect to the wild strains, when a threshold of about 50% of ITNs coverage highlights the hypothesis of a behaviour selection. A sensitivity analysis has shown that the top three parameters that play a dominant role on the mosquito fitness are the proportion of individuals using bed nets and its effectiveness, the impact of bed nets on mosquito oviposition, and the mosquito genetic plasticity related to changing in biting time. Conclusion By taking the evolutionary aspect into account, the model was able to show that the long-term use of ITNs, although representing an undisputed success in reducing malaria incidence and mortality in many affected areas, is not free of undesirable side effects. From the evolutionary point of view of the parasite virulence, it should be expected that plasmodium parasites would be under pressure to reduce their virulence. This speculative hypothesis can eventually be demonstrated in the medium to long-term use of ITNs.
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Affiliation(s)
- Claudia P Ferreira
- Departamento de Bioestatística, IBB, UNESP, Botucatu, SP, 18618-689, Brazil
| | - Silas P Lyra
- Departamento de Bioestatística, IBB, UNESP, Botucatu, SP, 18618-689, Brazil
| | - Franciane Azevedo
- Faculdade de Computação e Engenharia Elétrica, UNIFESSPA, Marabá, PA, 68507-590, Brazil
| | - David Greenhalgh
- Department of Mathematics and Statistics, University of Strathclyde, Glasgow, G1 1XH, Scotland
| | - Eduardo Massad
- School of Medicine, University of São Paulo, São Paulo, SP, 01246-903, Brazil.
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Reiner RC, Guerra C, Donnelly MJ, Bousema T, Drakeley C, Smith DL. Estimating malaria transmission from humans to mosquitoes in a noisy landscape. J R Soc Interface 2016; 12:20150478. [PMID: 26400195 PMCID: PMC4614487 DOI: 10.1098/rsif.2015.0478] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
A basic quantitative understanding of malaria transmission requires measuring the probability a mosquito becomes infected after feeding on a human. Parasite prevalence in mosquitoes is highly age-dependent, and the unknown age-structure of fluctuating mosquito populations impedes estimation. Here, we simulate mosquito infection dynamics, where mosquito recruitment is modelled seasonally with fractional Brownian noise, and we develop methods for estimating mosquito infection rates. We find that noise introduces bias, but the magnitude of the bias depends on the ‘colour' of the noise. Some of these problems can be overcome by increasing the sampling frequency, but estimates of transmission rates (and estimated reductions in transmission) are most accurate and precise if they combine parity, oocyst rates and sporozoite rates. These studies provide a basis for evaluating the adequacy of various entomological sampling procedures for measuring malaria parasite transmission from humans to mosquitoes and for evaluating the direct transmission-blocking effects of a vaccine.
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Affiliation(s)
- Robert C Reiner
- Fogarty International Center, National Institutes of Health, Bethesda, MD, USA Department of Entomology, University of California, Davis, CA, USA Department of Epidemiology and Biostatistics, Indiana University, Bloomington, IN, USA
| | - Carlos Guerra
- Center for Disease Dynamics, Economics and Policy, Washington, DC, USA
| | - Martin J Donnelly
- Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK Malaria Programme, Wellcome Trust Sanger Institute, Cambridge, UK
| | - Teun Bousema
- Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, UK Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Chris Drakeley
- Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, UK
| | - David L Smith
- Fogarty International Center, National Institutes of Health, Bethesda, MD, USA Sanaria Institute for Global Health and Tropical Medicine, Rockville, MD, USA Department of Zoology, University of Oxford, Oxford, UK Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, USA
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Hamainza B, Sikaala CH, Moonga HB, Chanda J, Chinula D, Mwenda M, Kamuliwo M, Bennett A, Seyoum A, Killeen GF. Incremental impact upon malaria transmission of supplementing pyrethroid-impregnated long-lasting insecticidal nets with indoor residual spraying using pyrethroids or the organophosphate, pirimiphos methyl. Malar J 2016; 15:100. [PMID: 26893012 PMCID: PMC4758014 DOI: 10.1186/s12936-016-1143-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Accepted: 02/04/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Long-lasting, insecticidal nets (LLINs) and indoor residual spraying (IRS) are the most widely accepted and applied malaria vector control methods. However, evidence that incremental impact is achieved when they are combined remains limited and inconsistent. METHODS Fourteen population clusters of approximately 1000 residents each in Zambia's Luangwa and Nyimba districts, which had high pre-existing usage rates (81.7 %) of pyrethroid-impregnated LLINs were quasi-randomly assigned to receive IRS with either of two pyrethroids, namely deltamethrin [Wetable granules (WG)] and lambdacyhalothrin [capsule suspension (CS)], with an emulsifiable concentrate (EC) or CS formulation of the organophosphate pirimiphos methyl (PM), or with no supplementary vector control measure. Diagnostic positivity of patients tested for malaria by community health workers in these clusters was surveyed longitudinally over pre- and post-treatment periods spanning 29 months, over which the treatments were allocated and re-allocated in advance of three sequential rainy seasons. RESULTS Supplementation of LLINs with PM CS offered the greatest initial level of protection against malaria in the first 3 months of application (incremental protective efficacy (IPE) [95 % confidence interval (CI)] = 0.63 [CI 0.57, 0.69], P < 0.001), followed by lambdacyhalothrin (IPE [95 % CI] = 0.31 [0.10, 0.47], P = 0.006) and PM EC (IPE, 0.23 [CI 0.15, 0.31], P < 0.001) and then by deltamethrin (IPE [95 % CI] = 0.19 [-0.01, 0.35], P = 0.064). Neither pyrethroid formulation provided protection beyond 3 months after spraying, but the protection provided by both PM formulations persisted undiminished for longer periods: 6 months for CS and 12 months for EC. The CS formulation of PM provided greater protection than the combined pyrethroid IRS formulations throughout its effective life IPE [95 % CI] = 0.79 [0.75, 0.83] over 6 months. The EC formulation of PM provided incremental protection for the first 3 months (IPE [95 % CI] = 0.23 [0.15, 0.31]) that was approximately equivalent to the two pyrethroid formulations (lambdacyhalothrin, IPE [95 % CI] = 0.31 [0.10, 0.47] and deltamethrin, IPE [95 % CI] = 0.19 [-0.01, 0.35]) but the additional protection provided by the former, apparently lasted an entire year. CONCLUSION Where universal coverage targets for LLIN utilization has been achieved, supplementing LLINs with IRS using pyrethroids may reduce malaria transmission below levels achieved by LLIN use alone, even in settings where pyrethroid resistance occurs in the vector population. However, far greater reduction of transmission can be achieved under such conditions by supplementing LLINs with IRS using non-pyrethroid insecticide classes, such as organophosphates, so this is a viable approach to mitigating and managing pyrethroid resistance.
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Affiliation(s)
- Busiku Hamainza
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
- Malaria Elimination Initiative, Global Health Group, University of California, 550 16th St., San Francisco, CA, 94158, USA.
| | - Chadwick H Sikaala
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
- Malaria Elimination Initiative, Global Health Group, University of California, 550 16th St., San Francisco, CA, 94158, USA.
| | - Hawela B Moonga
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
| | - Javan Chanda
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
| | - Dingani Chinula
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
| | - Mulenga Mwenda
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
| | - Mulakwa Kamuliwo
- National Malaria Control Centre, Ministry of Health, Chainama Hospital, College Grounds, off Great East road, PO Box 32509, Lusaka, Zambia.
| | - Adam Bennett
- Malaria Elimination Initiative, Global Health Group, University of California, 550 16th St., San Francisco, CA, 94158, USA.
| | - Aklilu Seyoum
- Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | - Gerry F Killeen
- Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
- Environmental Health and Ecological Sciences Thematic Group, Ifakara Health Institute, PO Box 53, Ifakara, Morogoro, United Republic of Tanzania.
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Feng X, Ruan S, Teng Z, Wang K. Stability and backward bifurcation in a malaria transmission model with applications to the control of malaria in China. Math Biosci 2015; 266:52-64. [DOI: 10.1016/j.mbs.2015.05.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Revised: 04/14/2015] [Accepted: 05/12/2015] [Indexed: 10/23/2022]
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Kiware SS, Corliss G, Merrill S, Lwetoijera DW, Devine G, Majambere S, Killeen GF. Predicting Scenarios for Successful Autodissemination of Pyriproxyfen by Malaria Vectors from Their Resting Sites to Aquatic Habitats; Description and Simulation Analysis of a Field-Parameterizable Model. PLoS One 2015; 10:e0131835. [PMID: 26186730 PMCID: PMC4505906 DOI: 10.1371/journal.pone.0131835] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 06/07/2015] [Indexed: 11/25/2022] Open
Abstract
Background Large-cage experiments indicate pyriproxifen (PPF) can be transferred from resting sites to aquatic habitats by Anopheles arabiensis - malaria vector mosquitoes to inhibit emergence of their own offspring. PPF coverage is amplified twice: (1) partial coverage of resting sites with PPF contamination results in far higher contamination coverage of adult mosquitoes because they are mobile and use numerous resting sites per gonotrophic cycle, and (2) even greater contamination coverage of aquatic habitats results from accumulation of PPF from multiple oviposition events. Methods and Findings Deterministic mathematical models are described that use only field-measurable input parameters and capture the biological processes that mediate PPF autodissemination. Recent successes in large cages can be rationalized, and the plausibility of success under full field conditions can be evaluated a priori. The model also defines measurable properties of PPF delivery prototypes that may be optimized under controlled experimental conditions to maximize chances of success in full field trials. The most obvious flaw in this model is the endogenous relationship that inevitably occurs between the larval habitat coverage and the measured rate of oviposition into those habitats if the target mosquito species is used to mediate PPF transfer. However, this inconsistency also illustrates the potential advantages of using a different, non-target mosquito species for contamination at selected resting sites that shares the same aquatic habitats as the primary target. For autodissemination interventions to eliminate malaria transmission or vector populations during the dry season window of opportunity will require comprehensive contamination of the most challenging subset of aquatic habitats (Clx) that persist or retain PPF activity (Ux) for only one week (Clx→1, where Ux = 7 days). To achieve >99% contamination coverage of these habitats will necessitate values for the product of the proportional coverage of the ovipositing mosquito population with PPF contamination (CM) by the ovitrap-detectable rates of oviposition by wild mosquitoes into this subset of habitats (mlx,z,d), divided by the titre of contaminated mosquitoes required to render them unproductive (Tlx,z,d), that approximately approach unity (CMmlx,z,d/Tlx,z,d→1). Conclusions The simple multiplicative relationship between CM and mlx,z,d/Tlx,z,d, and the simple exponential decay effect they have upon uncontaminated aquatic habitats, allows application of this model by theoreticians and field biologists alike.
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Affiliation(s)
- Samson S. Kiware
- Environmental Health and Ecological Sciences Thematic Group, Ifakara |Health Institute, P.O. Box 53, Ifakara, Tanzania
- Department of Mathematics, Statistics and Computer Science, Marquette University, Milwaukee, WI, 53201–1881, United States of America
- * E-mail:
| | - George Corliss
- Department of Mathematics, Statistics and Computer Science, Marquette University, Milwaukee, WI, 53201–1881, United States of America
| | - Stephen Merrill
- Department of Mathematics, Statistics and Computer Science, Marquette University, Milwaukee, WI, 53201–1881, United States of America
| | - Dickson W. Lwetoijera
- Environmental Health and Ecological Sciences Thematic Group, Ifakara |Health Institute, P.O. Box 53, Ifakara, Tanzania
- Liverpool School of Tropical Medicine, Vector Biology Department, Pembroke Place, Liverpool, L3 5QA, United Kingdom
| | - Gregor Devine
- QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
| | - Silas Majambere
- Environmental Health and Ecological Sciences Thematic Group, Ifakara |Health Institute, P.O. Box 53, Ifakara, Tanzania
- Liverpool School of Tropical Medicine, Vector Biology Department, Pembroke Place, Liverpool, L3 5QA, United Kingdom
| | - Gerry F. Killeen
- Environmental Health and Ecological Sciences Thematic Group, Ifakara |Health Institute, P.O. Box 53, Ifakara, Tanzania
- Liverpool School of Tropical Medicine, Vector Biology Department, Pembroke Place, Liverpool, L3 5QA, United Kingdom
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Briët OJT, Huho BJ, Gimnig JE, Bayoh N, Seyoum A, Sikaala CH, Govella N, Diallo DA, Abdullah S, Smith TA, Killeen GF. Applications and limitations of Centers for Disease Control and Prevention miniature light traps for measuring biting densities of African malaria vector populations: a pooled-analysis of 13 comparisons with human landing catches. Malar J 2015; 14:247. [PMID: 26082036 PMCID: PMC4470360 DOI: 10.1186/s12936-015-0761-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Accepted: 06/02/2015] [Indexed: 11/20/2022] Open
Abstract
Background Measurement of densities of host-seeking malaria vectors is important for estimating levels of disease transmission, for appropriately allocating interventions, and for quantifying their impact. The gold standard for estimating mosquito—human contact rates is the human landing catch (HLC), where human volunteers catch mosquitoes that land on their exposed body parts. This approach necessitates exposure to potentially infectious mosquitoes, and is very labour intensive. There are several safer and less labour-intensive methods, with Centers for Disease Control light traps (LT) placed indoors near occupied bed nets being the most widely used. Methods This paper presents analyses of 13 studies with paired mosquito collections of LT and HLC to evaluate these methods for their consistency in sampling indoor-feeding mosquitoes belonging to the two major taxa of malaria vectors across Africa, the Anopheles gambiae sensu lato complex and the Anopheles funestus s.l. group. Both overall and study-specific sampling efficiencies of LT compared with HLC were computed, and regression methods that allow for the substantial variations in mosquito counts made by either method were used to test whether the sampling efficacy varies with mosquito density. Results Generally, LT were able to collect similar numbers of mosquitoes to the HLC indoors, although the relative sampling efficacy, measured by the ratio of LT:HLC varied considerably between studies. The overall best estimate for An. gambiae s.l. was 1.06 (95% credible interval: 0.68–1.64) and for An. funestus s.l. was 1.37 (0.70–2.68). Local calibration exercises are not reproducible, since only in a few studies did LT sample proportionally to HLC, and there was no geographical pattern or consistent trend with average density in the tendency for LT to either under- or over-sample. Conclusions LT are a crude tool at best, but are relatively easy to deploy on a large scale. Spatial and temporal variation in mosquito densities and human malaria transmission exposure span several orders of magnitude, compared to which the inconsistencies of LT are relatively small. LT, therefore, remain an invaluable and safe alternative to HLC for measuring indoor malaria transmission exposure in Africa. Electronic supplementary material The online version of this article (doi:10.1186/s12936-015-0761-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Olivier J T Briët
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Socinstrasse 57, 4002, Basel, Switzerland. .,University of Basel, Petersplatz 1, Basel, 4003, Switzerland.
| | - Bernadette J Huho
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Socinstrasse 57, 4002, Basel, Switzerland. .,University of Basel, Petersplatz 1, Basel, 4003, Switzerland. .,Ifakara Health Institute, PO Box 78373, Dar es Salaam, United Republic of Tanzania.
| | - John E Gimnig
- Centre for Global Health Research, Kenya Medical Research Institute, PO Box 1578, Kisumu, Kenya. .,Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, 4770 Buford Highway, Mailstop F-42, Atlanta, GA, 30341, USA.
| | - Nabie Bayoh
- Centre for Global Health Research, Kenya Medical Research Institute, PO Box 1578, Kisumu, Kenya. .,Centers for Disease Control and Prevention, PO Box 1578, Kisumu, Kenya.
| | - Aklilu Seyoum
- Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | - Chadwick H Sikaala
- Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK. .,National Malaria Control Centre, Chainama Hospital College Grounds, Off Great East Road, PO Box 32509, Lusaka, Zambia.
| | - Nicodem Govella
- Ifakara Health Institute, PO Box 78373, Dar es Salaam, United Republic of Tanzania.
| | - Diadier A Diallo
- Centre National de Recherche et de Formation sur le Paludisme (CNRFP), 01 BP 2208, Ouagadougou 01, Ouagadougou, Burkina Faso.
| | - Salim Abdullah
- Ifakara Health Institute, PO Box 78373, Dar es Salaam, United Republic of Tanzania.
| | - Thomas A Smith
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Socinstrasse 57, 4002, Basel, Switzerland. .,University of Basel, Petersplatz 1, Basel, 4003, Switzerland.
| | - Gerry F Killeen
- Ifakara Health Institute, PO Box 78373, Dar es Salaam, United Republic of Tanzania. .,Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
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Smith DL, Perkins TA, Reiner RC, Barker CM, Niu T, Chaves LF, Ellis AM, George DB, Le Menach A, Pulliam JRC, Bisanzio D, Buckee C, Chiyaka C, Cummings DAT, Garcia AJ, Gatton ML, Gething PW, Hartley DM, Johnston G, Klein EY, Michael E, Lloyd AL, Pigott DM, Reisen WK, Ruktanonchai N, Singh BK, Stoller J, Tatem AJ, Kitron U, Godfray HCJ, Cohen JM, Hay SI, Scott TW. Recasting the theory of mosquito-borne pathogen transmission dynamics and control. Trans R Soc Trop Med Hyg 2014; 108:185-97. [PMID: 24591453 PMCID: PMC3952634 DOI: 10.1093/trstmh/tru026] [Citation(s) in RCA: 111] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Mosquito-borne diseases pose some of the greatest challenges in public health, especially
in tropical and sub-tropical regions of the world. Efforts to control these diseases have
been underpinned by a theoretical framework developed for malaria by Ross and Macdonald,
including models, metrics for measuring transmission, and theory of control that
identifies key vulnerabilities in the transmission cycle. That framework, especially
Macdonald's formula for R0 and its entomological derivative,
vectorial capacity, are now used to study dynamics and design interventions for many
mosquito-borne diseases. A systematic review of 388 models published between 1970 and 2010
found that the vast majority adopted the Ross–Macdonald assumption of homogeneous
transmission in a well-mixed population. Studies comparing models and data question these
assumptions and point to the capacity to model heterogeneous, focal transmission as the
most important but relatively unexplored component in current theory. Fine-scale
heterogeneity causes transmission dynamics to be nonlinear, and poses problems for
modeling, epidemiology and measurement. Novel mathematical approaches show how
heterogeneity arises from the biology and the landscape on which the processes of mosquito
biting and pathogen transmission unfold. Emerging theory focuses attention on the
ecological and social context for mosquito blood feeding, the movement of both hosts and
mosquitoes, and the relevant spatial scales for measuring transmission and for modeling
dynamics and control.
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Affiliation(s)
- David L Smith
- Department of Epidemiology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, USA
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14
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A Realistic Host-Vector Transmission Model for Describing Malaria Prevalence Pattern. Bull Math Biol 2013; 75:2499-528. [DOI: 10.1007/s11538-013-9905-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 09/19/2013] [Indexed: 01/05/2023]
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Abstract
South Africa is considering major health service restructuring to move towards a universal system. This calls for understanding the challenges in the existing health system. The paper, therefore, comprehensively evaluates an aspect of current health system performance - the benefit incidence of health services. It seeks to understand how the benefits from using health services in South Africa are currently distributed across socio-economic groups. Using a nationally representative household survey, results show that lower socio-economic groups benefit less than their richer counterparts from both public and private sector health services, and that the distribution of service benefits is not in line with their need for care.
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Killeen GF, Chitnis N, Moore SJ, Okumu FO. Target product profile choices for intra-domiciliary malaria vector control pesticide products: repel or kill? Malar J 2011; 10:207. [PMID: 21798023 PMCID: PMC3199905 DOI: 10.1186/1475-2875-10-207] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Accepted: 07/28/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The most common pesticide products for controlling malaria-transmitting mosquitoes combine two distinct modes of action: 1) conventional insecticidal activity which kills mosquitoes exposed to the pesticide and 2) deterrence of mosquitoes away from protected humans. While deterrence enhances personal or household protection of long-lasting insecticidal nets and indoor residual sprays, it may also attenuate or even reverse communal protection if it diverts mosquitoes to non-users rather than killing them outright. METHODS A process-explicit model of malaria transmission is described which captures the sequential interaction between deterrent and toxic actions of vector control pesticides and accounts for the distinctive impacts of toxic activities which kill mosquitoes before or after they have fed upon the occupant of a covered house or sleeping space. RESULTS Increasing deterrency increases personal protection but consistently reduces communal protection because deterrent sub-lethal exposure inevitably reduces the proportion subsequently exposed to higher lethal doses. If the high coverage targets of the World Health Organization are achieved, purely toxic products with no deterrence are predicted to generally provide superior protection to non-users and even users, especially where vectors feed exclusively on humans and a substantial amount of transmission occurs outdoors. Remarkably, this is even the case if that product confers no personal protection and only kills mosquitoes after they have fed. CONCLUSIONS Products with purely mosquito-toxic profiles may, therefore, be preferable for programmes with universal coverage targets, rather than those with equivalent toxicity but which also have higher deterrence. However, if purely mosquito-toxic products confer little personal protection because they do not deter mosquitoes and only kill them after they have fed, then they will require aggressive "catch up" campaigns, with behaviour change communication strategies that emphasize the communal nature of protection, to achieve high coverage rapidly.
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Affiliation(s)
- Gerry F Killeen
- Biomedical & Environmental Thematic Group, Ifakara Health Institute, Ifakara, Kilombero District, Morogoro Region, Tanzania.
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Ermert V, Fink AH, Jones AE, Morse AP. Development of a new version of the Liverpool Malaria Model. II. Calibration and validation for West Africa. Malar J 2011; 10:62. [PMID: 21410939 PMCID: PMC3070689 DOI: 10.1186/1475-2875-10-62] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Accepted: 03/16/2011] [Indexed: 11/21/2022] Open
Abstract
Background In the first part of this study, an extensive literature survey led to the construction of a new version of the Liverpool Malaria Model (LMM). A new set of parameter settings was provided and a new development of the mathematical formulation of important processes related to the vector population was performed within the LMM. In this part of the study, so far undetermined model parameters are calibrated through the use of data from field studies. The latter are also used to validate the new LMM version, which is furthermore compared against the original LMM version. Methods For the calibration and validation of the LMM, numerous entomological and parasitological field observations were gathered for West Africa. Continuous and quality-controlled temperature and precipitation time series were constructed using intermittent raw data from 34 weather stations across West Africa. The meteorological time series served as the LMM data input. The skill of LMM simulations was tested for 830 different sets of parameter settings of the undetermined LMM parameters. The model version with the highest skill score in terms of entomological malaria variables was taken as the final setting of the new LMM version. Results Validation of the new LMM version in West Africa revealed that the simulations compare well with entomological field observations. The new version reproduces realistic transmission rates and simulated malaria seasons are comparable to field observations. Overall the new model version performs much better than the original model. The new model version enables the detection of the epidemic malaria potential at fringes of endemic areas and, more importantly, it is now applicable to the vast area of malaria endemicity in the humid African tropics. Conclusions A review of entomological and parasitological data from West Africa enabled the construction of a new LMM version. This model version represents a significant step forward in the modelling of a weather-driven malaria transmission cycle. The LMM is now more suitable for the use in malaria early warning systems as well as for malaria projections based on climate change scenarios, both in epidemic and endemic malaria areas.
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Affiliation(s)
- Volker Ermert
- Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany.
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18
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Escalante A, Gattuso M, Pérez P, Zacchino S. Evidence for the mechanism of action of the antifungal phytolaccoside B isolated from Phytolacca tetramera Hauman. JOURNAL OF NATURAL PRODUCTS 2008; 71:1720-1725. [PMID: 18816139 DOI: 10.1021/np070660i] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Phytolaccoside B (1), an antifungal monodesmoside triterpenoid glycoside isolated from berries of Phytolacca tetramera Hauman (Phytolaccaceae), alters the morphology of yeasts and molds. The malformations were similar to those produced by enfumafungin, a known inhibitor of (1-->3)-beta-D-glucan synthase, an enzyme that catalyzes the synthesis of (1-->3)-beta-D-glucan, one of the major polymers of the fungal cell wall. However, enzymatic assays revealed that 1 did not inhibit (1-->3)-beta-D-glucan synthase, but it did produce a notable enhancement of the chitin synthase 1 activity and, concomitantly, a rise in chitin, another important polymer of the fungal cell walls. This finding was corroborated by fluorescence microscopy and also by quantification of the chitin. In addition, a 2-fold increase in the thickness of the fungal cell wall was observed with transmission electronic microscopy. On the other hand, 1 neither bound to ergosterol nor caused hemolysis of red blood cells, although some fungal membrane damage was observed at the MIC of 1.
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Affiliation(s)
- Andrea Escalante
- Area Farmacognosia, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina
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Chitnis N, Hyman JM, Cushing JM. Determining important parameters in the spread of malaria through the sensitivity analysis of a mathematical model. Bull Math Biol 2008; 70:1272-96. [PMID: 18293044 DOI: 10.1007/s11538-008-9299-0] [Citation(s) in RCA: 409] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Accepted: 11/20/2007] [Indexed: 11/24/2022]
Abstract
We perform sensitivity analyses on a mathematical model of malaria transmission to determine the relative importance of model parameters to disease transmission and prevalence. We compile two sets of baseline parameter values: one for areas of high transmission and one for low transmission. We compute sensitivity indices of the reproductive number (which measures initial disease transmission) and the endemic equilibrium point (which measures disease prevalence) to the parameters at the baseline values. We find that in areas of low transmission, the reproductive number and the equilibrium proportion of infectious humans are most sensitive to the mosquito biting rate. In areas of high transmission, the reproductive number is again most sensitive to the mosquito biting rate, but the equilibrium proportion of infectious humans is most sensitive to the human recovery rate. This suggests strategies that target the mosquito biting rate (such as the use of insecticide-treated bed nets and indoor residual spraying) and those that target the human recovery rate (such as the prompt diagnosis and treatment of infectious individuals) can be successful in controlling malaria.
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Affiliation(s)
- Nakul Chitnis
- Department of Public Health and Epidemiology, Swiss Tropical Institute, Socinstrasse 57, Postfach, 4002, Basel, Switzerland.
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Ndiaye PI, Bicout DJ, Mondet B, Sabatier P. Rainfall triggered dynamics of Aedes mosquito aggressiveness. J Theor Biol 2006; 243:222-9. [PMID: 16876201 DOI: 10.1016/j.jtbi.2006.06.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Revised: 06/04/2006] [Accepted: 06/07/2006] [Indexed: 10/24/2022]
Abstract
Inspired by Davidson method of estimating daily survivals of a structureless population of mosquitoes, we present a model which describes the behavior of floodwater mosquitoes in terms of emergence functions following a rainfall event, blood feeding frequency and parous stages, and survival at various stages. As a generalization of the Davidson formula, we have developed an approach for dealing with the dynamics of structured population of mosquitoes, and derived various formulas allowing assessment of demographic parameters like durations of gonotrophic cycles and (apparent) daily survivals. The method was subsequently applied to field data of floodwater mosquitoes Aedes vexans arabiensis, potential vectors of Rift Valley fever in West Africa, collected during the 2003 rainy season in Barkedji, Senegal. We found that mosquitoes emerged about 3 to 4 days following an efficient rainfall, and mosquito emergences, described by a bell shaped function, lasted for about 2 days. The mean duration of the gonotrophic cycle was 3 days and the apparent daily survival about 0.87.
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Affiliation(s)
- P I Ndiaye
- Biomathematics and Epidemiology, EPSP - TIMC/ENVL, B.P. 83, 69280 Marcy l'Etoile, France
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Dolo G, Briët OJT, Dao A, Traoré SF, Bouaré M, Sogoba N, Niaré O, Bagayogo M, Sangaré D, Teuscher T, Touré YT. Malaria transmission in relation to rice cultivation in the irrigated Sahel of Mali. Acta Trop 2004; 89:147-59. [PMID: 14732237 DOI: 10.1016/j.actatropica.2003.10.014] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Seven cross-sectional entomological surveys were carried out from September 1995 to February 1998 in three irrigated rice growing villages and three villages without irrigated agriculture in the area surrounding Niono, located 350km north-east of Bamako, Mali. The transmission pattern differed markedly between the two zones. In the irrigated zone, the transmission of malaria was fairly constant over the seasons at a low level. In the non-irrigated zone, transmission was mostly below detection level during the dry season, whereas it was high toward the end of the rainy season. In the irrigated zone, high densities of mosquitoes were correlated with low anthropophily, low sporozoite indices and probably low survival rates. In the non-irrigated zone, mosquito densities were lower and these relationships were less pronounced. Differential use of mosquito nets in the two zones may have been an important factor in the observed differences in transmission. The presence of cattle may also have played an important role. Two mosquito-catching methods (human landing catch and spray catch) were compared.
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Affiliation(s)
- Guimogo Dolo
- Département d'Epidémiologie des Affections Parasitaires, Faculté de Médecine, de Pharmacie et d'Odonto-Stomatologie, BP 1805, Bamako, Mali
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