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Mutono N, Basáñez MG, James A, Stolk WA, Makori A, Kimani TN, Hollingsworth TD, Vasconcelos A, Dixon MA, de Vlas SJ, Thumbi SM. Elimination of transmission of onchocerciasis (river blindness) with long-term ivermectin mass drug administration with or without vector control in sub-Saharan Africa: a systematic review and meta-analysis. Lancet Glob Health 2024; 12:e771-e782. [PMID: 38484745 PMCID: PMC11009120 DOI: 10.1016/s2214-109x(24)00043-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2023] [Revised: 01/11/2024] [Accepted: 01/19/2024] [Indexed: 04/15/2024]
Abstract
BACKGROUND WHO has proposed elimination of transmission of onchocerciasis (river blindness) by 2030. More than 99% of cases of onchocerciasis are in sub-Saharan Africa. Vector control and mass drug administration of ivermectin have been the main interventions for many years, with varying success. We aimed to identify factors associated with elimination of onchocerciasis transmission in sub-Saharan Africa. METHODS For this systematic review and meta-analysis we searched for published articles reporting epidemiological or entomological assessments of onchocerciasis transmission status in sub-Saharan Africa, with or without vector control. We searched MEDLINE, PubMed, Web of Science, Embase, Cochrane Central Register of Controlled Trials, African Index Medicus, and Google Scholar databases for all articles published from database inception to Aug 19, 2023, without language restrictions. The search terms used were "onchocerciasis" AND "ivermectin" AND "mass drug administration". The three inclusion criteria were (1) focus or foci located in Africa, (2) reporting of elimination of transmission or at least 10 years of ivermectin mass drug administration in the focus or foci, and (3) inclusion of at least one of the following assessments: microfilarial prevalence, nodule prevalence, Ov16 antibody seroprevalence, and blackfly infectivity prevalence. Epidemiological modelling studies and reviews were excluded. Four reviewers (NM, AJ, AM, and TNK) extracted data in duplicate from the full-text articles using a data extraction tool developed in Excel with columns recording the data of interest to be extracted, and a column where important comments for each study could be highlighted. We did not request any individual-level data from authors. Foci were classified as achieving elimination of transmission, being close to elimination of transmission, or with ongoing transmission. We used mixed-effects meta-regression models to identify factors associated with transmission status. This study is registered in PROSPERO, CRD42022338986. FINDINGS Of 1525 articles screened after the removal of duplicates, 75 provided 282 records from 238 distinct foci in 19 (70%) of the 27 onchocerciasis-endemic countries in sub-Saharan Africa. Elimination of transmission was reported in 24 (9%) records, being close to elimination of transmission in 86 (30%) records, and ongoing transmission in 172 (61%) records. I2 was 83·3% (95% CI 79·7 to 86·3). Records reporting 10 or more years of continuous mass drug administration with 80% or more therapeutic coverage of the eligible population yielded significantly higher odds of achieving elimination of transmission (log-odds 8·5 [95% CI 3·5 to 13·5]) or elimination and being close to elimination of transmission (42·4 [18·7 to 66·1]) than those with no years achieving 80% coverage or more. Reporting 15-19 years of ivermectin mass drug administration (22·7 [17·2 to 28·2]) and biannual treatment (43·3 [27·2 to 59·3]) were positively associated with elimination and being close to elimination of transmission compared with less than 15 years and no biannual mass drug administration, respectively. Having had vector control without vector elimination (-42·8 [-59·1 to -26·5]) and baseline holoendemicity (-41·97 [-60·6 to -23·2]) were associated with increased risk of ongoing transmission compared with no vector control and hypoendemicity, respectively. Blackfly disappearance due to vector control or environmental change contributed to elimination of transmission. INTERPRETATION Mass drug administration duration, frequency, and coverage; baseline endemicity; and vector elimination or disappearance are important determinants of elimination of onchocerciasis transmission in sub-Saharan Africa. Our findings underscore the importance of improving and sustaining high therapeutic coverage and increasing treatment frequency if countries are to achieve elimination of onchocerciasis transmission. FUNDING The Bill & Melinda Gates Foundation and Neglected Tropical Diseases Modelling Consortium, UK Medical Research Council, and Global Health EDCTP3 Joint Undertaking. TRANSLATIONS For the Swahili, French, Spanish and Portuguese translations of the abstract see Supplementary Materials section.
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Affiliation(s)
- Nyamai Mutono
- Centre for Epidemiological Modelling and Analysis, University of Nairobi, Nairobi, Kenya; Paul G Allen School for Global Health, Washington State University, Pullman, WA, USA.
| | - Maria-Gloria Basáñez
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK; London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
| | - Ananthu James
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, Netherlands
| | - Wilma A Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, Netherlands
| | - Anita Makori
- Centre for Epidemiological Modelling and Analysis, University of Nairobi, Nairobi, Kenya; Paul G Allen School for Global Health, Washington State University, Pullman, WA, USA
| | - Teresia Njoki Kimani
- Centre for Epidemiological Modelling and Analysis, University of Nairobi, Nairobi, Kenya; Paul G Allen School for Global Health, Washington State University, Pullman, WA, USA; Ministry of Health Kenya, Kiambu Town, Kenya
| | | | | | - Matthew A Dixon
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK; London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, Netherlands
| | - S M Thumbi
- Centre for Epidemiological Modelling and Analysis, University of Nairobi, Nairobi, Kenya; Paul G Allen School for Global Health, Washington State University, Pullman, WA, USA; Institute of Immunology and Infection Research, University of Edinburgh, Edinburgh, UK
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Ngwili N, Sentamu DN, Korir M, Adriko M, Beinamaryo P, Dione MM, Kaducu JM, Mubangizi A, Mwinzi PN, Thomas LF, Dixon MA. Spatial and temporal distribution of Taenia solium and its risk factors in Uganda. Int J Infect Dis 2023; 129:274-284. [PMID: 36805327 DOI: 10.1016/j.ijid.2023.02.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Revised: 01/30/2023] [Accepted: 02/02/2023] [Indexed: 02/17/2023] Open
Abstract
OBJECTIVES The lack of subnational mapping of the zoonotic cestode Taenia solium in endemic countries presents a major challenge to achieving intensified T. solium control milestones, as outlined in the "World Health Organization neglected tropical disease roadmap by 2030". We conducted a mapping study in Uganda, considered to be endemic, to identify subnational high-risk areas. METHODS T. solium prevalence data, adjusted for diagnostic sensitivity and specificity in a Bayesian framework, were identified through a systematic review. Spatial autocorrelation and interpolation techniques were used to transform demographic and health survey cluster-level sanitation and poverty indicators, overlaid onto a pig density map for Uganda into modelled porcine cysticercosis (PCC) risk maps. RESULTS A total of 16 articles (n = 11 PCC and n = 5 human cysticercosis (HCC) and/or human taeniasis) were included in the final analysis. The observed HCC prevalence ranged from 0.01% to 6.0% (confidence interval range: 0.004-11.4%), whereas the adjusted PCC ranged from 0.3 to 93.9% (uncertainty interval range: 0-99.8%). There was substantial variation in the modelled PCC risk factors and prevalence across Uganda and over time. CONCLUSION The high PCC prevalence and moderate HCC exposure estimates indicate the need for urgent implementation of T. solium control efforts in Uganda.
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Affiliation(s)
- Nicholas Ngwili
- Animal and Human Health Program, International Livestock Research Institute, Nairobi, Kenya
| | - Derrick N Sentamu
- Animal and Human Health Program, International Livestock Research Institute, Nairobi, Kenya
| | - Max Korir
- Animal and Human Health Program, International Livestock Research Institute, Nairobi, Kenya
| | - Moses Adriko
- Vector Borne and Neglected Tropical Disease Control Division, Ministry of Health, Kampala, Uganda
| | - Prudence Beinamaryo
- Vector Borne and Neglected Tropical Disease Control Division, Ministry of Health, Kampala, Uganda
| | - Michel M Dione
- International Livestock Research Institute, c/o AfricaRice, Dakar, Senegal
| | - Joyce Moriku Kaducu
- Ministry of Health: Hon. State Minister of Health, Primary Care, Kampala, Uganda
| | - Alfred Mubangizi
- Vector Borne and Neglected Tropical Disease Control Division, Ministry of Health, Kampala, Uganda
| | - Pauline Ngina Mwinzi
- The Expanded Special Project for Elimination of NTDs, World Health Organization, Regional Office for Africa, Brazzaville, Congo
| | - Lian F Thomas
- Animal and Human Health Program, International Livestock Research Institute, Nairobi, Kenya; Institute of Infection, Veterinary & Ecological Sciences, The University of Liverpool, Leahurst Campus, Neston, UK
| | - Matthew A Dixon
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, UK; SCI Foundation, Edinburgh House, London, UK; MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, UK.
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Dixon MA, Winskill P, Harrison WE, Whittaker C, Schmidt V, Flórez Sánchez AC, Cucunuba ZM, Edia-Asuke AU, Walker M, Basáñez MG. Global variation in force-of-infection trends for human T aenia solium taeniasis/cysticercosis. eLife 2022; 11:76988. [PMID: 35984416 PMCID: PMC9391040 DOI: 10.7554/elife.76988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 08/07/2022] [Indexed: 12/01/2022] Open
Abstract
Infection by Taenia solium poses a major burden across endemic countries. The World Health Organization (WHO) 2021–2030 Neglected Tropical Diseases roadmap has proposed that 30% of endemic countries achieve intensified T. solium control in hyperendemic areas by 2030. Understanding geographical variation in age-prevalence profiles and force-of-infection (FoI) estimates will inform intervention designs across settings. Human taeniasis (HTT) and human cysticercosis (HCC) age-prevalence data from 16 studies in Latin America, Africa, and Asia were extracted through a systematic review. Catalytic models, incorporating diagnostic performance uncertainty, were fitted to the data using Bayesian methods, to estimate rates of antibody (Ab)-seroconversion, infection acquisition and Ab-seroreversion or infection loss. HCC FoI and Ab-seroreversion rates were also estimated across 23 departments in Colombia from 28,100 individuals. Across settings, there was extensive variation in all-ages seroprevalence. Evidence for Ab-seroreversion or infection loss was found in most settings for both HTT and HCC and for HCC Ab-seroreversion in Colombia. The average duration until humans became Ab-seropositive/infected decreased as all-age (sero)prevalence increased. There was no clear relationship between the average duration humans remain Ab-seropositive and all-age seroprevalence. Marked geographical heterogeneity in T. solium transmission rates indicate the need for setting-specific intervention strategies to achieve the WHO goals.
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Affiliation(s)
- Matthew A Dixon
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.,SCI Foundation, Edinburgh House, London, United Kingdom
| | - Peter Winskill
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
| | | | - Charles Whittaker
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
| | - Veronika Schmidt
- Department of Neurology, Center for Global Health, Technical University Munich (TUM), Munich, Germany.,Centre for Global Health, Institute of Health and Society, University of Oslo, Oslo, Norway
| | | | - Zulma M Cucunuba
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
| | | | - Martin Walker
- Department of Pathobiology and Population Sciences and London Centre for Neglected Tropical Disease Research (LCNTDR), Royal Veterinary College, Hatfield, United Kingdom
| | - María-Gloria Basáñez
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.,MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
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Jewell PD, Abraham A, Schmidt V, Buell KG, Bustos JA, Garcia HH, Dixon MA, Walker M, Ngowi BJ, Basáñez MG, Winkler AS. Neurocysticercosis and HIV/AIDS co-infection: A scoping review. Trop Med Int Health 2021; 26:1140-1152. [PMID: 34228854 DOI: 10.1111/tmi.13652] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVES Neurocysticercosis (NCC) and human immunodeficiency virus (HIV) have a high disease burden and are prevalent in overlapping low- and middle-income areas. Yet, treatment guidance for people living with HIV/AIDS (PLWH/A) co-infected with NCC is currently lacking. This study aims to scope the available literature on HIV/AIDS and NCC co-infection, focusing on epidemiology, clinical characteristics, diagnostics and treatment outcomes. METHODS The scoping literature review methodological framework, and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. A total of 16,969 records identified through database searching, and 45 additional records from other sources were reduced to 52 included studies after a standardised selection process. RESULTS Two experimental studies, ten observational studies, 23 case series/case reports and 17 reviews or letters were identified. Observational studies demonstrated similar NCC seroprevalence in PLWH/A and their HIV-negative counterparts. Of 29 PLWH/A and NCC co-infection, 17 (59%) suffered from epileptic seizures, 15 (52%) from headaches and 15 (52%) had focal neurological deficits. Eighteen (62%) had viable vesicular cysts, and six (21%) had calcified cysts. Fifteen (52%) were treated with albendazole, of which 11 (73%) responded well to treatment. Five individuals potentially demonstrated an immune-reconstitution inflammatory syndrome after commencing antiretroviral therapy, although this was in the absence of immunological and neuroimaging confirmation. CONCLUSIONS There is a paucity of evidence to guide treatment of PLWH/A and NCC co-infection. There is a pressing need for high-quality studies in this patient group to appropriately inform diagnostic and management guidelines for HIV-positive patients with NCC.
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Affiliation(s)
- Paul D Jewell
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research, Imperial College London, London, UK
| | - Annette Abraham
- Department of Neurology, Center for Global Health, School of Medicine, Technical University of Munich, Munich, Germany.,Department of Community Medicine and Global Health, Centre for Global Health, Institute of Health and Society, University of Oslo, Oslo, Norway
| | - Veronika Schmidt
- Department of Neurology, Center for Global Health, School of Medicine, Technical University of Munich, Munich, Germany.,Department of Community Medicine and Global Health, Centre for Global Health, Institute of Health and Society, University of Oslo, Oslo, Norway
| | - Kevin G Buell
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research, Imperial College London, London, UK
| | - Javier A Bustos
- Center for Global Health, Universidad Peruana Cayetano Heredia, Lima, Peru.,Cysticercosis Unit, Instituto Nacional de Ciencias Neurológicas, Lima, Peru
| | - Hector H Garcia
- Center for Global Health, Universidad Peruana Cayetano Heredia, Lima, Peru.,Cysticercosis Unit, Instituto Nacional de Ciencias Neurológicas, Lima, Peru
| | - Matthew A Dixon
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research, Imperial College London, London, UK.,Department of Infectious Disease Epidemiology, MRC Centre for Global Infectious Disease Analysis, Imperial College London, London, UK.,Schistosomiasis Control Initiative Foundation, London, UK
| | - Martin Walker
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research, Imperial College London, London, UK.,Department of Pathobiology and Population Sciences, London Centre for Neglected Tropical Disease Research, Royal Veterinary College, Hatfield, UK
| | - Bernard J Ngowi
- Muhimbili Medical Research Centre, National Institute for Medical Research, Dar es Salaam, Tanzania.,College of Health and Allied Sciences, University of Dar es Salaam, Dar es Salaam, Tanzania
| | - Maria-Gloria Basáñez
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research, Imperial College London, London, UK.,Department of Infectious Disease Epidemiology, MRC Centre for Global Infectious Disease Analysis, Imperial College London, London, UK
| | - Andrea S Winkler
- Department of Neurology, Center for Global Health, School of Medicine, Technical University of Munich, Munich, Germany.,Department of Community Medicine and Global Health, Centre for Global Health, Institute of Health and Society, University of Oslo, Oslo, Norway
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Dixon MA, Winskill P, Harrison WE, Basáñez MG. Taenia solium taeniasis/cysticercosis: From parasite biology and immunology to diagnosis and control. Adv Parasitol 2021; 112:133-217. [PMID: 34024358 DOI: 10.1016/bs.apar.2021.03.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Infection with the pork tapeworm (Taenia solium) is responsible for a substantial global burden of disease, not only restricted to its impact on human health, but also resulting in a considerable economic burden to smallholder pig farmers due to pig cysticercosis infection. The life-cycle, parasitology and immunology of T. solium are complex, involving pigs (the intermediate host, harbouring the larval metacestode stage), humans (the definitive host, harbouring the adult tapeworm, in addition to acting as accidental intermediate hosts) and the environment (the source of infection with eggs/proglottids). We review the parasitology, immunology, and epidemiology of the infection associated with each of the T. solium life-cycle stages, including the pre-adult/adult tapeworm responsible for human taeniasis; post-oncosphere and cysticercus associated with porcine and human cysticercosis, and the biological characteristics of eggs in the environment. We discuss the burden associated, in endemic settings, with neurocysticercosis (NCC) in humans, and the broader cross-sectoral economic impact associated both with NCC and porcine cysticercosis, the latter impacting food-value chains. Existing tools for diagnostics and control interventions that target different stages of the T. solium transmission cycle are reviewed and their limitations discussed. Currently, no national T. solium control programmes have been established in endemic areas, with further work required to identify optimal strategies according to epidemiological setting. There is increasing evidence suggesting that cross-sectoral interventions which target the parasite in both the human and pig host provide the most effective approaches for achieving control and ultimately elimination. We discuss future avenues for research on T. solium to support the attainment of the goals proposed in the revised World Health Organisation neglected tropical diseases roadmap for 2021-2030 adopted at the 73rd World Health Assembly in November 2020.
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Affiliation(s)
- Matthew A Dixon
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom; MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom; Schistosomiasis Control Initiative Foundation (SCI Foundation), London, United Kingdom
| | - Peter Winskill
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
| | - Wendy E Harrison
- Schistosomiasis Control Initiative Foundation (SCI Foundation), London, United Kingdom
| | - Maria-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom; MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.
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Clark J, Stolk WA, Basáñez MG, Coffeng LE, Cucunubá ZM, Dixon MA, Dyson L, Hampson K, Marks M, Medley GF, Pollington TM, Prada JM, Rock KS, Salje H, Toor J, Hollingsworth TD. How modelling can help steer the course set by the World Health Organization 2021-2030 roadmap on neglected tropical diseases. Gates Open Res 2021; 5:112. [PMID: 35169682 PMCID: PMC8816801 DOI: 10.12688/gatesopenres.13327.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/28/2022] [Indexed: 01/12/2023] Open
Abstract
The World Health Organization recently launched its 2021-2030 roadmap, Ending the Neglect to Attain the Sustainable Development Goals , an updated call to arms to end the suffering caused by neglected tropical diseases. Modelling and quantitative analyses played a significant role in forming these latest goals. In this collection, we discuss the insights, the resulting recommendations and identified challenges of public health modelling for 13 of the target diseases: Chagas disease, dengue, gambiense human African trypanosomiasis (gHAT), lymphatic filariasis (LF), onchocerciasis, rabies, scabies, schistosomiasis, soil-transmitted helminthiases (STH), Taenia solium taeniasis/ cysticercosis, trachoma, visceral leishmaniasis (VL) and yaws. This piece reflects the three cross-cutting themes identified across the collection, regarding the contribution that modelling can make to timelines, programme design, drug development and clinical trials.
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Affiliation(s)
- Jessica Clark
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Old Road Campus, Headington, Oxford, OX3 7LF, UK
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Wilma A. Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, 3000 CA, The Netherlands
| | - María-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - Luc E. Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, 3000 CA, The Netherlands
| | - Zulma M. Cucunubá
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - Matthew A. Dixon
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
- Schistosomiasis Control Initiative Foundation, London, SE11 5DP, UK
| | - Louise Dyson
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Katie Hampson
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Michael Marks
- Department of Clinical Research, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
| | - Graham F. Medley
- Centre for Mathematical Modelling of Infectious Disease, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London, WC1H 9SH, UK
| | - Timothy M. Pollington
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Old Road Campus, Headington, Oxford, OX3 7LF, UK
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK
| | - Joaquin M. Prada
- School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, GU2 7AL, UK
| | - Kat S. Rock
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK
| | - Henrik Salje
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH, UK
| | - Jaspreet Toor
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - T. Déirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Old Road Campus, Headington, Oxford, OX3 7LF, UK
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Clark J, Stolk WA, Basáñez MG, Coffeng LE, Cucunubá ZM, Dixon MA, Dyson L, Hampson K, Marks M, Medley GF, Pollington TM, Prada JM, Rock KS, Salje H, Toor J, Hollingsworth TD. How modelling can help steer the course set by the World Health Organization 2021-2030 roadmap on neglected tropical diseases. Gates Open Res 2021; 5:112. [PMID: 35169682 PMCID: PMC8816801 DOI: 10.12688/gatesopenres.13327.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/13/2021] [Indexed: 01/12/2023] Open
Abstract
The World Health Organization recently launched its 2021-2030 roadmap, Ending the Neglect to Attain the Sustainable Development Goals , an updated call to arms to end the suffering caused by neglected tropical diseases. Modelling and quantitative analyses played a significant role in forming these latest goals. In this collection, we discuss the insights, the resulting recommendations and identified challenges of public health modelling for 13 of the target diseases: Chagas disease, dengue, gambiense human African trypanosomiasis (gHAT), lymphatic filariasis (LF), onchocerciasis, rabies, scabies, schistosomiasis, soil-transmitted helminthiases (STH), Taenia solium taeniasis/ cysticercosis, trachoma, visceral leishmaniasis (VL) and yaws. This piece reflects the three cross-cutting themes identified across the collection, regarding the contribution that modelling can make to timelines, programme design, drug development and clinical trials.
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Affiliation(s)
- Jessica Clark
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Old Road Campus, Headington, Oxford, OX3 7LF, UK
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Wilma A. Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, 3000 CA, The Netherlands
| | - María-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - Luc E. Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, 3000 CA, The Netherlands
| | - Zulma M. Cucunubá
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - Matthew A. Dixon
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
- Schistosomiasis Control Initiative Foundation, London, SE11 5DP, UK
| | - Louise Dyson
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Katie Hampson
- Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Michael Marks
- Department of Clinical Research, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
- Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK
| | - Graham F. Medley
- Centre for Mathematical Modelling of Infectious Disease, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London, WC1H 9SH, UK
| | - Timothy M. Pollington
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Old Road Campus, Headington, Oxford, OX3 7LF, UK
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK
| | - Joaquin M. Prada
- School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, GU2 7AL, UK
| | - Kat S. Rock
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK
| | - Henrik Salje
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH, UK
| | - Jaspreet Toor
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - T. Déirdre Hollingsworth
- Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, University of Oxford, Old Road Campus, Headington, Oxford, OX3 7LF, UK
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Dixon MA, Winskill P, Harrison WE, Whittaker C, Schmidt V, Sarti E, Bawm S, Dione MM, Thomas LF, Walker M, Basáñez MG. Force-of-infection of Taenia solium porcine cysticercosis: a modelling analysis to assess global incidence and prevalence trends. Sci Rep 2020; 10:17637. [PMID: 33077748 PMCID: PMC7572398 DOI: 10.1038/s41598-020-74007-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Accepted: 09/14/2020] [Indexed: 11/26/2022] Open
Abstract
The World Health Organization (WHO) called, in 2012, for a validated strategy towards Taenia solium taeniasis/cysticercosis control and elimination. Estimating pig force-of-infection (FoI, the average rate at which susceptible pigs become infected) across geographical settings will help understand local epidemiology and inform effective intervention design. Porcine cysticercosis (PCC) age-prevalence data (from 15 studies in Latin America, Africa and Asia) were identified through systematic review. Catalytic models were fitted to the data using Bayesian methods, incorporating uncertainty in diagnostic performance, to estimate rates of antibody seroconversion, viable metacestode acquisition, and seroreversion/infection loss. There was evidence of antibody seroreversion across 5 studies, and of infection loss in 6 studies measured by antigen or necropsy, indicating transient serological responses and natural resolution of infection. Concerted efforts should be made to collect robust data using improved diagnostics to better understand geographical heterogeneities in T. solium transmission to support post-2020 WHO targets.
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Affiliation(s)
- Matthew A Dixon
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, London, W2 1PG, UK.
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, W2 1PG, UK.
| | - Peter Winskill
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, W2 1PG, UK
| | - Wendy E Harrison
- SCI Foundation, Edinburgh House, 170 Kennington Lane, London, SE11 5DP, UK
| | - Charles Whittaker
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, W2 1PG, UK
| | - Veronika Schmidt
- Department of Neurology, Center for Global Health, Technical University Munich (TUM), Munich, Germany
- Centre for Global Health, Institute of Health and Society, University of Oslo, Oslo, Norway
| | - Elsa Sarti
- Sanofi Pasteur Latin America, Av. Universidad N° 1738, Colonia Coyoacán, 04000, Mexico, D.F., Mexico
| | - Saw Bawm
- University of Veterinary Science, Yezin, Nay Pyi Taw, 15013, Myanmar
| | - Michel M Dione
- International Livestock Research Institute, 01 BP 1496, Ouagadougou, Burkina Faso
| | - Lian F Thomas
- International Livestock Research Institute (ILRI), Old Naivasha Road, PO Box 30709-00100, Nairobi, Kenya
- Institute for Infection and Global Health, University of Liverpool, 8 West Derby Street, Liverpool, L69 7BE, UK
| | - Martin Walker
- Department of Pathobiology and Population Sciences and London Centre for Neglected Tropical Disease Research (LCNTDR), Royal Veterinary College, Hatfield, AL9 7TA, UK
| | - Maria-Gloria Basáñez
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research (LCNTDR), Faculty of Medicine, School of Public Health, Imperial College London, London, W2 1PG, UK
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, W2 1PG, UK
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Dixon MA, Braae UC, Winskill P, Devleesschauwer B, Trevisan C, Van Damme I, Walker M, Hamley JID, Ramiandrasoa SN, Schmidt V, Gabriël S, Harrison W, Basáñez MG. Modelling for Taenia solium control strategies beyond 2020. Bull World Health Organ 2020; 98:198-205. [PMID: 32132754 PMCID: PMC7047036 DOI: 10.2471/blt.19.238485] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 12/15/2019] [Accepted: 12/27/2019] [Indexed: 01/06/2023] Open
Abstract
The cestode Taenia solium is responsible for a considerable cross-sectoral health and economic burden due to human neurocysticercosis and porcine cysticercosis. The 2012 World Health Organization (WHO) roadmap for neglected tropical diseases called for the development of a validated strategy for control of T. solium; however, such a strategy is not yet available. In 2019, WHO launched a global consultation aimed at refining the post-2020 targets for control of T. solium for a new roadmap for neglected tropical diseases. In response, two groups working on taeniasis and cysticercosis mathematical models (cystiSim and EPICYST models), together with a range of other stakeholders organized a workshop to provide technical input to the WHO consultation and develop a research plan to support efforts to achieve the post-2020 targets. The workshop led to the formation of a collaboration, CystiTeam, which aims to tackle the population biology, transmission dynamics, epidemiology and control of T. solium through mathematical modelling approaches. In this paper, we outline developments in T. solium control and in particular the use of modelling to help achieve post-2020 targets for control of T. solium. We discuss the steps involved in improving confidence in the predictive capacities of existing mathematical and computational models on T. solium transmission, including model comparison, refinement, calibration and validation. Expanding the CystiTeam partnership to other research groups and stakeholders, particularly those operating in different geographical and endemic areas, will enhance the prospects of improving the applicability of T. solium transmission models to inform taeniasis and cysticercosis control strategies.
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Affiliation(s)
- Matthew A Dixon
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research and MRC Centre for Global Infectious Disease Analysis, Imperial College London, London W2 1PG, England
| | - Uffe C Braae
- Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | - Peter Winskill
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research and MRC Centre for Global Infectious Disease Analysis, Imperial College London, London W2 1PG, England
| | | | - Chiara Trevisan
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Inge Van Damme
- Department of Veterinary Public Health and Food Safety, Ghent University, Merelbeke, Belgium
| | - Martin Walker
- Department of Pathobiology and Population Sciences, Royal Veterinary College, Hatfield, England
| | - Jonathan I D Hamley
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research and MRC Centre for Global Infectious Disease Analysis, Imperial College London, London W2 1PG, England
| | - Sylvia N Ramiandrasoa
- Service de Lutte contre les Maladies Endémiques et Négligées, Ministry of Public Health, Antananarivo, Madagascar
| | - Veronika Schmidt
- Department of Neurology, Technical University Munich, Munich, Germany
| | - Sarah Gabriël
- Department of Veterinary Public Health and Food Safety, Ghent University, Merelbeke, Belgium
| | - Wendy Harrison
- Schistosomiasis Control Initiative Foundation, London, England
| | - Maria-Gloria Basáñez
- Department of Infectious Disease Epidemiology, London Centre for Neglected Tropical Disease Research and MRC Centre for Global Infectious Disease Analysis, Imperial College London, London W2 1PG, England
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Betson M, Alonte AJI, Ancog RC, Aquino AMO, Belizario VY, Bordado AMD, Clark J, Corales MCG, Dacuma MG, Divina BP, Dixon MA, Gourley SA, Jimenez JRD, Jones BP, Manalo SMP, Prada JM, van Vliet AHM, Whatley KCL, Paller VGV. Zoonotic transmission of intestinal helminths in southeast Asia: Implications for control and elimination. Adv Parasitol 2020; 108:47-131. [PMID: 32291086 DOI: 10.1016/bs.apar.2020.01.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Intestinal helminths are extremely widespread and highly prevalent infections of humans, particularly in rural and poor urban areas of low and middle-income countries. These parasites have chronic and often insidious effects on human health and child development including abdominal problems, anaemia, stunting and wasting. Certain animals play a fundamental role in the transmission of many intestinal helminths to humans. However, the contribution of zoonotic transmission to the overall burden of human intestinal helminth infection and the relative importance of different animal reservoirs remains incomplete. Moreover, control programmes and transmission models for intestinal helminths often do not consider the role of zoonotic reservoirs of infection. Such reservoirs will become increasingly important as control is scaled up and there is a move towards interruption and even elimination of parasite transmission. With a focus on southeast Asia, and the Philippines in particular, this review summarises the major zoonotic intestinal helminths, risk factors for infection and highlights knowledge gaps related to their epidemiology and transmission. Various methodologies are discussed, including parasite genomics, mathematical modelling and socio-economic analysis, that could be employed to improve understanding of intestinal helminth spread, reservoir attribution and the burden associated with infection, as well as assess effectiveness of interventions. For sustainable control and ultimately elimination of intestinal helminths, there is a need to move beyond scheduled mass deworming and to consider animal and environmental reservoirs. A One Health approach to control of intestinal helminths is proposed, integrating interventions targeting humans, animals and the environment, including improved access to water, hygiene and sanitation. This will require coordination and collaboration across different sectors to achieve best health outcomes for all.
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Affiliation(s)
- Martha Betson
- University of Surrey, Guildford, Surrey, United Kingdom.
| | | | - Rico C Ancog
- University of the Philippines Los Baños, Laguna, Philippines
| | | | | | | | - Jessica Clark
- University of Surrey, Guildford, Surrey, United Kingdom
| | | | | | - Billy P Divina
- University of the Philippines Los Baños, Laguna, Philippines
| | | | | | | | - Ben P Jones
- University of Surrey, Guildford, Surrey, United Kingdom
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Walker M, Stolk WA, Dixon MA, Bottomley C, Diawara L, Traoré MO, de Vlas SJ, Basáñez MG. Modelling the elimination of river blindness using long-term epidemiological and programmatic data from Mali and Senegal. Epidemics 2018; 18:4-15. [PMID: 28279455 PMCID: PMC5340858 DOI: 10.1016/j.epidem.2017.02.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2016] [Revised: 02/03/2017] [Accepted: 02/07/2017] [Indexed: 11/11/2022] Open
Abstract
Onchocerciasis is earmarked for elimination in some African countries by 2020/2025. 15+ years of ivermectin treatment drove infection prevalence to zero in areas of Mali & Senegal. Data-driven model projections are used to evaluate the risk of infection resurgence. Latent infections can initiate slow resurgence in communities with high transmission propensity. Highly sensitive and long-term surveillance will be necessary to verify elimination.
The onchocerciasis transmission models EPIONCHO and ONCHOSIM have been independently developed and used to explore the feasibility of eliminating onchocerciasis from Africa with mass (annual or biannual) distribution of ivermectin within the timeframes proposed by the World Health Organization (WHO) and endorsed by the 2012 London Declaration on Neglected Tropical Diseases (i.e. by 2020/2025). Based on the findings of our previous model comparison, we implemented technical refinements and tested the projections of EPIONCHO and ONCHOSIM against long-term epidemiological data from two West African transmission foci in Mali and Senegal where the observed prevalence of infection was brought to zero circa 2007–2009 after 15–17 years of mass ivermectin treatment. We simulated these interventions using programmatic information on the frequency and coverage of mass treatments and trained the model projections using longitudinal parasitological data from 27 communities, evaluating the projected outcome of elimination (local parasite extinction) or resurgence. We found that EPIONCHO and ONCHOSIM captured adequately the epidemiological trends during mass treatment but that resurgence, while never predicted by ONCHOSIM, was predicted by EPIONCHO in some communities with the highest (inferred) vector biting rates and associated pre-intervention endemicities. Resurgence can be extremely protracted such that low (microfilarial) prevalence between 1% and 5% can be maintained for 3–5 years before manifesting more prominently. We highlight that post-treatment and post-elimination surveillance protocols must be implemented for long enough and with high enough sensitivity to detect possible residual latent infections potentially indicative of resurgence. We also discuss uncertainty and differences between EPIONCHO and ONCHOSIM projections, the potential importance of vector control in high-transmission settings as a complementary intervention strategy, and the short remaining timeline for African countries to be ready to stop treatment safely and begin surveillance in order to meet the impending 2020/2025 elimination targets.
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Affiliation(s)
- Martin Walker
- Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK; Department of Pathobiology and Population Sciences and London Centre for Neglected Tropical Disease Research, Royal Veterinary College, Hawkshead Lane, Hatfield, AL9 7TA, UK.
| | - Wilma A Stolk
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Matthew A Dixon
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK; Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK
| | - Christian Bottomley
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK
| | - Lamine Diawara
- Inter-Country Support Team for West Africa, World Health Organization 158, Place de l'Indépendance 03 BP 7019, Ouagadougou 03, Burkina Faso
| | - Mamadou O Traoré
- Programme National de Lutte contre l'Onchocercose (PNLO), Direction Nationale de la Santé (DNS), B.P. 233, Bamako, Mali
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - María-Gloria Basáñez
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands; MRC Tropical Epidemiology Group, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK; Department of Infectious Disease Epidemiology and London Centre for Neglected Tropical Disease Research, Imperial College London, Norfolk Place, W2 1 PG, London, UK
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12
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Winskill P, Harrison WE, French MD, Dixon MA, Abela-Ridder B, Basáñez MG. Assessing the impact of intervention strategies against Taenia solium cysticercosis using the EPICYST transmission model. Parasit Vectors 2017; 10:73. [PMID: 28183336 PMCID: PMC5301381 DOI: 10.1186/s13071-017-1988-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 01/14/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The pork tapeworm, Taenia solium, and associated human infections, taeniasis, cysticercosis and neurocysticercosis, are serious public health problems, especially in developing countries. The World Health Organization (WHO) has set goals for having a validated strategy for control and elimination of T. solium taeniasis/cysticercosis by 2015 and interventions scaled-up in selected countries by 2020. Timely achievement of these internationally-endorsed targets requires that the relative benefits and effectiveness of potential interventions be explored rigorously within a quantitative framework. METHODS A deterministic, compartmental transmission model (EPICYST) was developed to capture the dynamics of the taeniasis/cysticercosis disease system in the human and pig hosts. Cysticercosis prevalence in humans, an outcome of high epidemiological and clinical importance, was explicitly modelled. A next generation matrix approach was used to derive an expression for the basic reproduction number, R 0. A full sensitivity analysis was performed using a methodology based on Latin-hypercube sampling partial rank correlation coefficient index. RESULTS EPICYST outputs indicate that chemotherapeutic intervention targeted at humans or pigs would be highly effective at reducing taeniasis and cysticercosis prevalence when applied singly, with annual chemotherapy of humans and pigs resulting, respectively, in 94 and 74% of human cysticercosis cases averted. Improved sanitation, meat inspection and animal husbandry are less effective but are still able to reduce prevalence singly or in combination. The value of R 0 for taeniasis was estimated at 1.4 (95% Credible Interval: 0.5-3.6). CONCLUSIONS Human- and pig-targeted drug-focussed interventions appear to be the most efficacious approach from the options currently available. The model presented is a forward step towards developing an informed control and elimination strategy for cysticercosis. Together with its validation against field data, EPICYST will be a valuable tool to help reach the WHO goals and to conduct economic evaluations of interventions in varying epidemiological settings.
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Affiliation(s)
- Peter Winskill
- Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
| | - Wendy E. Harrison
- Schistosomiasis Control Initiative, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St. Mary’s Campus, London, W2 1PG UK
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
| | - Michael D. French
- Schistosomiasis Control Initiative, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St. Mary’s Campus, London, W2 1PG UK
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
- Current address: Research Triangle Institute, 701 13st Street NW, Washington D.C., 20005 USA
| | - Matthew A. Dixon
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
| | - Bernadette Abela-Ridder
- Neglected Zoonotic Diseases Team, Department of Neglected Tropical Diseases (NTD), World Health Organization (WHO), 20 Avenue Appia, 1211, Geneva 27, Switzerland
| | - María-Gloria Basáñez
- Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine, Imperial College London, St Mary’s Campus, London, W2 1PG UK
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Affiliation(s)
| | - Osman A Dar
- Chatham House Centre on Global Health Security, Chatham House, 10 St James's Square, London SW1Y 4LE, UK, e-mail:
| | - David L Heymann
- Public Health England, Wellington House, 133-155 Waterloo Road, London SE1 8UG, UK, e-mail:
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Karesh WB, Dobson A, Lloyd-Smith JO, Lubroth J, Dixon MA, Bennett M, Aldrich S, Harrington T, Formenty P, Loh EH, Machalaba CC, Thomas MJ, Heymann DL. Ecology of zoonoses: natural and unnatural histories. Lancet 2012; 380. [PMID: 23200502 PMCID: PMC7138068 DOI: 10.1016/s0140-6736(12)61678-x] [Citation(s) in RCA: 440] [Impact Index Per Article: 36.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
More than 60% of human infectious diseases are caused by pathogens shared with wild or domestic animals. Zoonotic disease organisms include those that are endemic in human populations or enzootic in animal populations with frequent cross-species transmission to people. Some of these diseases have only emerged recently. Together, these organisms are responsible for a substantial burden of disease, with endemic and enzootic zoonoses causing about a billion cases of illness in people and millions of deaths every year. Emerging zoonoses are a growing threat to global health and have caused hundreds of billions of US dollars of economic damage in the past 20 years. We aimed to review how zoonotic diseases result from natural pathogen ecology, and how other circumstances, such as animal production, extraction of natural resources, and antimicrobial application change the dynamics of disease exposure to human beings. In view of present anthropogenic trends, a more effective approach to zoonotic disease prevention and control will require a broad view of medicine that emphasises evidence-based decision making and integrates ecological and evolutionary principles of animal, human, and environmental factors. This broad view is essential for the successful development of policies and practices that reduce probability of future zoonotic emergence, targeted surveillance and strategic prevention, and engagement of partners outside the medical community to help improve health outcomes and reduce disease threats.
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15
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Seino KK, Long MT, Gibbs EPJ, Bowen RA, Beachboard SE, Humphrey PP, Dixon MA, Bourgeois MA. Comparative efficacies of three commercially available vaccines against West Nile Virus (WNV) in a short-duration challenge trial involving an equine WNV encephalitis model. Clin Vaccine Immunol 2007; 14:1465-71. [PMID: 17687109 PMCID: PMC2168174 DOI: 10.1128/cvi.00249-07] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used a severe challenge model that produces clinical West Nile virus (WNV) disease to test the efficacy of three commercially available equine WNV vaccines in horses. Twenty-four healthy, WNV-seronegative horses of varying ages and genders were placed, in random and blind manner, into three trial groups consisting of eight horses each; two horses in each group received (i) an inactivated WNV vaccine (K-WN), (ii) a modified-live vaccine (CP-WN) containing the WNV prM and E proteins expressed by a canarypox vector, (iii) a live-chimera vaccine (WN-FV) containing WNV prM and E proteins expressed in a YF17D vector, or (iv) a diluent control. Challenge by this model caused grave neurological signs, viremia, moderate to severe histopathologic lesions in the brain and spinal cord, and an outcome of 0% survivorship in all six control horses. In contrast, challenge in horses at between 28 days postvaccination with the chimera vaccine and 56 days postvaccination with the commercial inactivated or modified-live vaccine resulted in 100% survivorship (protection from the onset of WNV encephalitis and viremia). Horses vaccinated with the live-chimera vaccine showed significantly fewer clinical signs than did the control horses (P </= 0.01) and the horses vaccinated with inactivated vaccine (P = 0.035). Mild residual inflammatory lesions were seen in a few of the vaccinated horses.
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Affiliation(s)
- K K Seino
- College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL 32610, USA.
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16
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Hora R, Kumar M, Kostrzynska M, Dixon MA, Warriner K. Inactivation of Escherichia coli O157:H7 and Salmonella on artificially or naturally contaminated mung beans (Vigna radiata L) using a stabilized oxychloro-based sanitizer. Lett Appl Microbiol 2007; 44:188-93. [PMID: 17257259 DOI: 10.1111/j.1472-765x.2006.02049.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
AIMS To evaluate the efficacy of a stabilized oxychloro-based (SOC) sanitizer to decontaminate mung beans artificially or naturally contaminated with Escherichia coli O157:H7 or Salmonella. METHODS AND RESULTS Naturally contaminated beans were produced by introducing a five-strain cocktail of E. coli O157:H7 or Salmonella onto the flowers of growing mung bean plants. Escherichia coli O157:H7 was only sporadically recovered from sprout lots (three testing positive from 10 tested) derived from harvested beans. In contrast, Salmonella was recovered from 18 of 20 lots screened. Pathogens present on naturally contaminated seed could be successfully inactivated with SOC applied at 200 ppm for 24 h at 28 degrees C. SOC treatment could also decontaminate artificially inoculated mung bean batches containing different levels of contaminated seed. SOC inactivated E. coli O157:H7, but not Salmonella introduced onto damaged (scarified) beans. CONCLUSIONS SOC sanitizer could inactivate Salmonella or E. coli O157:H7 naturally or artificially introduced onto mung beans. However, the SOC treatment failed to inactivate Salmonella introduced onto damaged mung beans. SIGNIFICANCE AND IMPACT OF THE STUDY SOC sanitizer represents an effective method for decontaminating undamaged mung beans.
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Affiliation(s)
- R Hora
- Department of Food Science, University of Guelph, Guelph, Ontario, Canada
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17
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Lund AM, Dixon MA, Vreken P, Leonard JV, Morris AAM. What is the role of medium-chain triglycerides in the management of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency? J Inherit Metab Dis 2003; 26:353-60. [PMID: 12971423 DOI: 10.1023/a:1025107119186] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Cardiomyopathy is common in infants with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Resolution of the cardiomyopathy can often be achieved by avoidance of fasting and changing from a conventional infant formula to one in which most long-chain fat is replaced by medium-chain triglycerides (MCT). It is uncertain whether the clinical improvement is due to the restriction of long-chain fat or whether the MCT have specific beneficial effects. To clarify this, the metabolic effects of MCT were examined in 5 patients. When given at around the level found in MCT-based infant formula, MCT had no effect on blood concentrations of ketone bodies, specific fatty acids or acylcarnitines. The present study cannot, however, exclude the possibility that MCT per se may have beneficial effects.
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Affiliation(s)
- A M Lund
- Metabolic Department, Great Ormond Street Hospital for Children, London, UK
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18
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Lund AM, Dixon MA, Vreken P, Leonard JV, Morris AAM. Plasma and erythrocyte fatty acid concentrations in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. J Inherit Metab Dis 2003; 26:410-2. [PMID: 12971430 DOI: 10.1023/a:1025175606891] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Plasma and erythrocyte fatty acids have been measured in 9 patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency being treated with a low-fat diet. No significant abnormality was detected and in particular docosahexaenoic acid was not deficient.
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Affiliation(s)
- A M Lund
- Metabolic Department, Great Ormond Street Hospital for Children, London, UK
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Darlington A, Dixon MA, Pilger C. The use of biofilters to improve indoor air quality: the removal of toluene, TCE, and formaldehyde. Life Support Biosph Sci 2001; 5:63-9. [PMID: 11540466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
A biofilter composed of a scrubber, a hydroponic planting system, and an aquatic system with green plants as a base maintained air quality within part of a modern office building. The scrubber was composed of five parallel fiberglass modules with external faces of porous lava rock. The face, largely covered with mosses, was wetted by recirculating water. Air was drawn through the scrubber and the immediately adjacent hydroponic region by a dedicated air handling system. The system was challenged for 4 weeks with three common indoor organic pollutants and removed significant amounts of all compounds. A single pass through the scrubber removed 10% of the trichloroethylene and 50% of the toluene. A single pass lowered formaldehyde air concentrations to 13 micrograms m-3 irrespective of influent levels (ranging between 30 and 90 micrograms m-3). The aquatic system accumulated trichloroethylene but neither toluene nor formaldehyde, suggesting the rapid breakdown of these materials. The botanical components removed some pollutants.
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Affiliation(s)
- A Darlington
- Department of Horticultural Science, University of Guelph, Canada.
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20
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Darlington AB, Dat JF, Dixon MA. The biofiltration of indoor air: air flux and temperature influences the removal of toluene, ethylbenzene, and xylene. Environ Sci Technol 2001; 35:240-246. [PMID: 11352020 DOI: 10.1021/es0010507] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
An alternative approach to maintaining indoor air quality may be the biofiltration of air circulated within the space. A biofilter with living botanical matter as the packing medium reduced concentrations of toluene, ethylbenzene, and o-xylene concurrently present at parts per billion (volume) in indoor air. The greatest reduction in concentrations per pass was under the slowest influent air flux (0.025 m s(-1)); however, the maximum amount removed per unit time occurred under the most rapid flux (0.2 m s(-1)). There was little difference between the different compounds with removal capacities of between 1.3 and 2.4 micromol m(-3) biofilter s(-1) (between 0.5 and 0.9 g m(-3) biofilter h(-1)) depending on influent flux and temperature. Contrary to biofilters subjected to higher influent concentrations, the optimal temperatures for removal by this biofilter decreased to less than 20 degrees C at the most rapid flux for all three compounds. Microbial activity was decreased at these cooler temperatures suggesting the biofilter was not microbially limited but rather was limited by the availability of substrate. The cooler temperatures allowed greater partitioning of the VOCs into the water column which had a greater impact on removal than its reduction in microbial activity.
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Affiliation(s)
- A B Darlington
- Department of Plant Agriculture, University of Guelph, Ontario, Canada.
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21
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Abstract
OBJECTIVES During intercurrent illness children with methylmalonic acidemia were found to have increased resting energy expenditure (REE). We measured REE in children with disorders of propionate metabolism (methylmalonic and propionic acidemia) when they were well and compared the values with those predicted by the Schofield equation. STUDY DESIGN Prospective study in tertiary care facility. REE was measured with open-circuit indirect calorimetry under standardized conditions. Predicted REE values were calculated with the Schofield equation. Fourteen subjects with propionic acidemia (n = 3) and methylmalonic acidemia (n = 11) were studied. RESULTS The median REE was 690 kcal/d (range 186 to 1687 kcal/d), which is significantly reduced, representing 80% +/- 18% of that predicted by the Schofield height and weight equation (P <.01). REE was significantly lower in female compared with male patients for unknown reasons. There were no differences with age or neurologic state. REE was not further reduced in those with chronic renal failure. CONCLUSION REE in patients with disorders of propionate metabolism is reduced when they are well.
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Affiliation(s)
- F Feillet
- Biochemistry, Endocrinology and Metabolism Unit, Institute of Child Health, London, United Kingdom
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22
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Abstract
An alternative method of maintaining indoor air quality may be through the biofiltration of air recirculating within the structure rather than the traditional approach of ventilation. This approach is currently being investigated. Prior to its acceptance for dealing with volatile organic compounds (VOCs) and CO2, efforts were made to determine whether the incorporation of this amount of biomass into the indoor space can have an (negative) impact on indoor air quality. A relatively large ecologically complex biofilter composed of a ca. 10 m2 bioscrubber, 30 m2 of plantings and a 3,500 litre aquarium were established in a 160 m2 'airtight' room in a recently constructed office building in downtown Toronto. This space maintained ca. 0.2 air changes per hour (ACH) compared to the 15 to 20 ACH (with a 30% refresh rate) of other spaces in the same building. Air quality parameters of concern were total VOCs (TVOCs), formaldehyde and aerial spore counts. TVOC and formaldehyde levels in the biofilter room were the same or significantly less than other spaces in the building despite a much slower refresh rate. Aerial spore levels were slightly higher than other indoor spaces but were well within reported values for 'healthy' indoor spaces. Levels appeared to be dependent on horticultural management practices within the space. Most genera of fungal spores present were common indoors and the other genera were associated with living or dead plant material or soil. From these results, the incorporation of a large amount of biomass associated with indoor biofilters does not in itself lower indoor air quality.
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Affiliation(s)
- A Darlington
- Department of Plant Agriculture, University of Guelph, Ontario, Canada
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23
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Abstract
Two sealed chambers were constructed, each measuring approximately 4.5 m x 3 m x 2.5 m (LxWxH). Heat exchangers and air handling components were integrated within the sealed environment. Construction materials were chosen to minimize off-gassing and oxidation. Acceptable materials included stainless steel, Teflon (TM), glass and Heresite (TM) or baked enamel coated metal parts. The glass-topped chambers have externally mounted microwave powered light sources providing minimum PAR at canopy level of 1000 micrometers m-2 s-1. Major gases (CO2, O2) were monitored. Other environmental variables relevant to plant production (humidity, temperature, nutrient solution) were monitored and controlled continuously. Typical environment control capability and system specifications are presented. The facility is described as a venue ideally suited to address specific research objectives in plant canopy light interception, such as the roles of novel microwave powered overhead and inner-canopy light sources for dense plant canopies. In addition, control of recycled hydroponic nutrient solutions and analysis of trace atmospheric hydrocarbons in the context of sealed environment life support can be concurrently monitored.
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Affiliation(s)
- M A Dixon
- Department of Horticultural Science, University of Guelph, Canada
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24
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Grodzinski B, Schmidt JM, Watts B, Taylor J, Bates S, Dixon MA, Staines H. Regulating plant/insect interactions using CO2 enrichment in model ecosystems. Adv Space Res 1999; 24:281-291. [PMID: 11542535 DOI: 10.1016/s0273-1177(99)00315-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The greenhouse environment is a challenging artificial ecosystem in which it is possible to study selected plant/insect interaction in a controlled environment. Due to a combination of "direct" and "indirect" effects of CO2 enrichment on plant photosynthesis and plant development, canopy productivity is generally increased. In this paper, we discuss the effects of daytime and nighttime CO2 enrichment protocols on gas exchange of pepper plants (Capsicum annuum L, cv Cubico) grown in controlled environments. In addition, we present the effects of thrips, a common Insect pest, on the photosynthetic and respiratory activity of these plant canopies. Carbon dioxide has diverse effects on the physiology and mortality of insects. However, our data indicate that thrips and whiteflies, at least, are not killed "directly" by CO2 levels used to enhance photosynthesis and plant growth. Together the data suggest that the insect population is affected "indirectly" by CO2 and that the primary effect of CO2 is via its effects on plant metabolism.
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Affiliation(s)
- B Grodzinski
- Department of Horticultural Science, University of Guelph, Canada
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25
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Abstract
208 motorists were observed at Florida International University, in Miami, Florida as part of a study of the influence of speed humps on motorists' behavior at pedestrian crossings. It was hypothesized that the presence of a speed hump will affect motorists' behavior by compelling them either to yield or stop at a pedestrian crossing to enable a pedestrian to cross safely. A between-subjects experimental design was employed to measure motorists' reactions. Analysis indicated that the relationship is strong between drivers' behavior and the presence or absence of this roadway stimulus. There was also evidence that female drivers may take more precautionary actions than male drivers. This information is useful for roadway designers and traffic psychologists.
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Affiliation(s)
- M A Dixon
- Department of Industrial and Systems Engineering, Florida International University, Miami 33174, USA
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26
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Cooper MJ, Lawson PK, Dixon MA, Zukowski E, Timms DN, Itoh F, Sakurai H, Kawata H, Tanaka Y, Ito M. Compton scattering study of 4f magnetism in CeFe2. Phys Rev B Condens Matter 1996; 54:4068-4074. [PMID: 9986307 DOI: 10.1103/physrevb.54.4068] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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27
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Abstract
Uncooked cornstarch (UCCS) loads in 14 patients with type 1 glycogenosis revealed that satisfactory glycaemia was achieved for a median of 4.25 hours (range 2.5 to 6). Length of glycaemia was related weakly to UCCS dose, but not to patient age or measures of metabolic control. Careful monitoring is required during UCCS treatment.
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Affiliation(s)
- P J Lee
- Medical Unit, Institute of Child Health, London
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28
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Lawson PK, Timms DN, Dixon MA, Cooper MJ, McCarthy JE, Hämäläinen K, Manninen S, Tschentscher T. The spin dependent momentum density of hexagonal close packed cobalt. J Xray Sci Technol 1996; 6:299-307. [PMID: 21307529 DOI: 10.3233/xst-1996-6306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Directional-spin-dependent Compton profiles of ferromagnetic hexagonal close packed cobalt metal have been measured with 117 keV and 167 keV circularly polarized synchrotron radiation at the new ESRF high energy beamline. Significantly improved resolution was achieved at the higher energy. The results have been compared with the profile predicted from an augmented plane wave (APW) calculation of the electron momentum density in the hexagonal phase. No significant difference was found between the c-axis and the basal plane magnetic profiles. The experiments show that there is substantially more 3d spin density at high momentum than in the model calculation. After correcting for this deficiency we find that the 4s-p component of the momentum density remains significantly different than predicted.
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Affiliation(s)
- P K Lawson
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
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29
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Abstract
In late life, depression is the most prevalent functional psychiatric disorder. Because the presentation may be multicausal and clinically complex, early assessment of biologic and psychosocial factors, diagnosis, and appropriate referral are important in ameliorating the associated morbidity and mortality. Nurses must have current knowledge and skills to assess mood states of elderly persons and to implement appropriate interventions. Successful management of depression in the elderly results in a reformulation of purpose and an enhanced quality of life.
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30
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Edwards DR, Dixon MA. Mechanisms of drought response in Thuja occidentalis L. I. Water stress conditioning and osmotic adjustment. Tree Physiol 1995; 15:121-127. [PMID: 14965984 DOI: 10.1093/treephys/15.2.121] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We investigated the extent of osmotic adjustment and changes in transpiration rate that occur in response to repeated cycles of water deficit stress in 6-year-old Thuja occidentalis L. (eastern white cedar) trees. Groups of trees were water-stress conditioned by repeated exposure to predetermined thresholds of nonlethal water stress by withholding water until the predawn water potential fell to -0.9 (mild conditioning) or -1.4 MPa (moderate conditioning). Both the mild and moderate conditioning treatments resulted in a decrease in osmotic potential of 0.08 to 0.20 MPa and 0.11 to 0.28 MPa, respectively, relative to the well-watered controls. Mildly and moderately conditioned trees exhibited an approximately 35 and 50% reduction in cumulative transpiration, respectively, following at least two stress cycles. Transpiration rates of conditioned trees remained below those of the well-watered controls even when water potential integrals were similar. We conclude that the decrease in transpiration rate was more important than osmotic adjustment as a mechanism of response to repeated water stress.
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Affiliation(s)
- D R Edwards
- Department of Horticultural Science, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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31
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Edwards DR, Dixon MA. Mechanisms of drought response in Thuja occidentalis L. II. Post-conditioning water stress and stress relief. Tree Physiol 1995; 15:129-133. [PMID: 14965985 DOI: 10.1093/treephys/15.2.129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We examined the extent of osmotic adjustment and the changes in relative water content (RWC) and transpiration rate (i.e., relative stomatal function) that occur in water-deficit-conditioned 6-year-old Thuja occidentalis L. (eastern white cedar) trees in response to a severe drought. Trees conditioned by successive cycles of mild or moderate nonlethal water stress (conditioning) and nonconditioned trees were exposed to drought (i.e., -2.0 MPa predawn water potential) to determine if water deficit conditioning enhanced tolerance to further drought stress. Following drought, all trees were well watered for 11 days to evaluate how quickly osmotic potential, RWC and transpiration rate returned to preconditioning values. Both nonconditioned trees and mildly conditioned trees exhibited similar responses to drought, whereas moderately conditioned trees maintained higher water potentials and transpiration rates were 38% lower. Both conditioned and nonconditioned trees exhibited a similar degree of osmotic adjustment (-0.39 MPa) in response to drought relative to the well-watered control trees. The well-watered control trees, nonconditioned trees and mildly conditioned trees had similar leaf RWCs that were about 3% lower than those of the moderately conditioned trees. Following the 11-day stress relief, there were no significant differences in osmotic potential between the well-watered control trees and any of the drought-treated trees. Daily transpiration rates and water potential integrals (WPI) of all drought-treated trees approached those of the well-watered control trees during the stress relief period. However, the relationship between cumulative transpiration and WPI showed that previous exposure to drought stress reduced transpiration rates. Leaf RWC of the moderately conditioned trees remained slightly higher than that of the nonconditioned and mildly conditioned trees.
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Affiliation(s)
- D R Edwards
- Department of Horticultural Science, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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32
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Abstract
Metabolic decompensation may occur in patients with disorders of intermediary metabolism during intercurrent illness. To prevent complications it is normal practice to change the diet to an 'emergency regimen'. The mainstay of this is a high carbohydrate intake, using soluble glucose polymer, given as frequent drinks by day and during the night. Additional therapy is given for some disorders. Practical details of the treatment are outlined.
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Dixon MA. 'Back to nursing'--a sham. Prof Nurse 1988; 3:119. [PMID: 3353404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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34
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Abstract
The response of excised stem segments of several tree species to freezing and thawing cycles was studied. All species studied (Thuja occidentalis, Fagus grandifolia, and Betula papyrifera) except maple (Acer spp.) exuded sap while freezing and absorbed on thawing. Maple stems absorbed sap while freezing and exuded sap during the thaw only when sucrose was present in the vessel solution. Increased concentration of sucrose in the vessel sap led to increased exudation. In the absence of sucrose, maple stems absorbed sap on thawing. The presence of sucrose enhanced sap absorption during freezing cycles in maples. In general, large sugars, disaccharides and larger, could substitute for sucrose in the maple exudation response while sugar hexoses could not. The results are discussed in relation to the O'Malley-Milburn model (1983 Can J Bot 61: 3100-3106) of sap flow in maples.
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Affiliation(s)
- R W Johnson
- Department of Botany, University of Toronto, Toronto, Ontario, Canada M5S 1A1
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35
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Abstract
We report the detection of cavitation events in corn (Zea mays) plants growing under field conditions in Greeley, CO. To our knowledge this study reports the first successful attempt to monitor continuously for long periods the cavitation events of a crop plant using acoustic detection techniques. Cavitation events occur in corn plants using acoustic detection techniques. Cavitation events occur in corn plants irrigated daily when the xylem pressure potentials fall below about -1.0 megapascals. In unirrigated corn we estimate that approximately half of all vessels cavitate on any one day when xylem pressure potentials fall below about -1.8 megapascals. We postulate that root pressure developed every night in irrigated and unirrigated corn is adequate to rejoin cavitated water columns.
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Affiliation(s)
- M T Tyree
- United States Department of Agriculture, Agricultural Research Service, Colorado State University, Fort Collins, Colorado 80521
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36
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Abstract
Family demographic characteristics, family structure, family environment, and help-seeking variables were explored through interviews with two groups of Afro-American adolescents, including 52 clients and 52 nonclients. One parent of each adolescent was also interviewed. The ratio of single-parent families in the two groups differed significantly. Using one-way analysis of variance, significant differences were found between the means of the groups on five of the ten Family Environment Scale (FES) subscales. The family groups differed significantly on only one help-seeking variable, use of formal helpers. Adolescent client families reported using formal helpers more than did adolescent nonclient families (F = 2.69; df 102; p less than 0.05).
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Tyree MT, Dixon MA, Tyree EL, Johnson R. Ultrasonic acoustic emissions from the sapwood of cedar and hemlock : an examination of three hypotheses regarding cavitations. Plant Physiol 1984; 75:988-92. [PMID: 16663774 PMCID: PMC1067038 DOI: 10.1104/pp.75.4.988] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Measurements are reported of ultrasonic acoustic emissions (AEs) measured from sapwood samples of Thuja occidentalis L. and Tsuga canadensis (L.) Carr. during air dehydration. The measurements were undertaken to test the following three hypotheses: (a) Each cavitation event produces one ultrasonic AE. (b) Large tracheids are more likely to cavitate than small tracheids. (c) When stem water potentials are >-0.4 MPa, a significant fraction of the water content of sapwood is held by ;capillary forces.' The last two hypotheses were recently discussed at length by M. H. Zimmermann. Experimental evidence consistent with all three hypotheses was obtained. The evidence for each hypothesis respectively is: (a) the cumulative number of AEs nearly equals the number of tracheids in small samples; (b) more water is lost per AE event at the beginning of the dehydration process than at the end, and (c) sapwood samples dehydrated from an initial water potential of 0 MPa lost significantly more water before AEs started than lost by samples dehydrated from an initial water potential of about -0.4 MPa. The extra water held by fully hydrated sapwood samples may have been capillary water as defined by Zimmerman.We also report an improved method for the measurement of the ;intensity' of ultrasonic AEs. Intensity is defined here as the area under the positive spikes of the AE signal (plotted as voltage versus time). This method was applied to produce a frequency histogram of the number of AEs versus intensity. A large fraction of the total number of AEs were of low intensity even in small samples (4 mm diameter by 10 mm length). This suggests that the effective ;listening distance' for most AEs was less than 5 to 10 mm.
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Affiliation(s)
- M T Tyree
- Department of Botany, University of Toronto, Toronto, Ontario M5S 1A1 Canada
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38
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Tyree MT, Dixon MA, Thompson RG. Ultrasonic Acoustic Emissions from the Sapwood of Thuja occidentalis Measured inside a Pressure Bomb. Plant Physiol 1984; 74:1046-9. [PMID: 16663501 PMCID: PMC1066816 DOI: 10.1104/pp.74.4.1046] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
An improved method of counting acoustic emission (AE) events from water-stressed stems of cedar (Thuja occidentalis L.) is presented. Amplified AEs are analyzed on a real time basis by a microcomputer. The instrumentation counts AE events in a fashion nearly analogous to scintillation counting of radioactive materials.The technique was applied to measuring ultrasonic AEs from the stems of cedar inside a pressure bomb. The shoots were originally fully hydrated. When the shoots are dehydrated in the bomb by application of an overpressure very few AEs were detected. When the bomb pressure is reduced after dehydration of the shoot, AE events could be detected. We conclude that ultrasonic AEs are caused by cavitation events (= structural breakdown of water columns in the tracheids of cedar) and not by the breaking of cellulose fibers in the wood.
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Affiliation(s)
- M T Tyree
- Department of Botany, University of Toronto, Toronto, Canada M5S 1A1
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39
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Tyree MT, Dixon MA. Cavitation Events in Thuja occidentalis L.? : Utrasonic Acoustic Emissions from the Sapwood Can Be Measured. Plant Physiol 1983; 72:1094-9. [PMID: 16663126 PMCID: PMC1066380 DOI: 10.1104/pp.72.4.1094] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Ultrasonic acoustic emissions (AE) in the frequency range of 0.1 to 1 megahertz appear to originate in the sapwood of Thuja occidentalis L. The AE are vibrations of an impulsive nature. The vibrations can be transduced to a voltage waveform and amplified. The vibrations of each AE event begin at a large amplitude which decays over 20 to 100 microseconds. Strong circumstantial evidence indicates that the ultrasonic AE result from cavitation events because: (a) they occur only when the xylem pressure potential Psi(xp) is more negative than a threshold level of about -1 megapascal; (b) the rate of AE events increases as Psi(xp) decreases and when the net rate of water loss increases; (c) the AE can be stopped by raising Psi(xp) above -1 megapascal. Ultrasonic AE have been measured in whole terminal shoots allowed to dry in the laboratory, in isolated pieces of sapwood as they dried in the laboratory, and in whole terminal shoots in a pressure bomb when Psi(xp) was decreased by lowering the gas pressure in the pressure bomb.
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Affiliation(s)
- M T Tyree
- Department of Botany, University of Toronto, Toronto, Canada M5S 1A1
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40
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Jameson P, Dixon MA, Grossberg SE. A sensitive interferon assay for many species of cells: encephalomyocarditis virus hemagglutinin yield reduction. Exp Biol Med (Maywood) 1977; 155:173-8. [PMID: 194253 DOI: 10.3181/00379727-155-39768] [Citation(s) in RCA: 43] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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