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Ecology and Control of the Trachoma Vector Musca Sorbens

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Ecology and Control of the Trachoma Vector Musca Sorbens Durham E-Theses Ecology and control of the trachoma vector Musca sorbens Emerson, Paul Michael How to cite: Emerson, Paul Michael (2001) Ecology and control of the trachoma vector Musca sorbens, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/3995/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk Ecology and control of the trachoma vector Musca sorbens Paul Michael Emerson The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. Department of Biological Sciences University of Durham Submitted for the degree of Doctor of Philosophy, December 2001 EcoBegy and control of the trachoma vector Musca sorbens Paul M. Emerson The work described in this thesis was conducted in rural Gambia and builds a body of evidence incriminating the fly Musca sorbens as a vector of the blinding disease, trachoma, which is caused by ocular infection with Chlamydia trachomatis. Literature on hygiene promotion, environmental change and flies and trachoma is reviewed in the context of the SAFE strategy for trachoma control advocated by the World Health Organization. M. sorbens was present throughout the year in trachoma endemic communities; was responsible for the majority of fly-eye contacts; C. trachomatis DNA was found on it; and trachoma transmission dropped when they were removed from the environment. In a large cluster-randomised trial communities receiving fly control with insecticide for six months had a mean reduction in trachoma prevalence of 56% (95% CI 19-93%; P=0.01) compared to controls and 37% (4-70%; P=0.068) fewer new prevalent cases of trachoma. Breeding media choice experiments showed that isolated human faeces were the preferred larval medium for M. sorbens and were capable of supporting the production of large numbers of adults. However, other animal faeces were also able to support M. sorbens development. This suggested that a community-based strategy to reduce the quantity of human faeces on the soil surface by providing latrines would have the effect of reducing the population of M. sorbens, and hence reduce fly-eye contact and trachoma transmission. The provision of latrines gave encouraging results, which were not statistically significant; 30% less active trachoma than controls after six months (-22-81%; P=0.210) and 28% (-5-60%; P=0.146) fewer new prevalent cases. Provision of latrines warrants further investigation as a method to control trachoma, particularly when used in conjunction with other control methods. The potential role of fly control in the SAFE strategy for trachoma control is discussed. AckDiowlledgemeinits Having the opportunity to conduct the work outlined in this thesis has often felt like a personal indulgence, and I am immensely grateful to have been able to devote the last four years to it. Many people have contributed to it's successful completion, and I wish to extend my thanks to them all. In particular to Steve Lindsay, my supervisor, mentor and friend, for giving me the freedom to aim for the goals that I wanted to, and the structure to help me attain them. To my field supervisors Robin Bailey and Gijs Walraven who have provided immeasurable help on the ground and always shown great belief in me, and commitment to the project. Robin Bailey additionally introduced the field of trachoma research to me, and me to those in the field of trachoma research, for which I am extremely grateful. The work was based at the Farafenni Field Station of the Medical Research Council Laboratories in The Gambia, and I wish to thank the following for their tireless effort and contribution to this work: Director, Keith McAdam; Station Administrator, Batch Cham; Field Supervisor, Mafuji Dibba; Field Staff, Pateh Bah, Mamadi Jallow, Tumani Kuyateh, Fama Manneh, Pateh Makalo, Yamundow Samba-Jallow, Ngansu Touray and Matarr Tunkara; Drivers, Tijan Cham, Babucar Njie, Karang Njie and Yaya Keita; Data manager, Maimuna Sowe; Data entry clerks, Mamaram Drammeh and Bakary Sonko and all the other support staff who kept the project going. The project was conducted in partnership with the Gambian National Eye Care Programme (NECP) and with the Gambian Government Department of Community Development (DCD). It would not have been possible to do the project without these partners and I wish to thank the following people for their commitment and unstinting support: NECP; Modou Bah, Bakary Ceesay, Hannah Faal, Sarjo Kanye, Kebba Lowe, Jerreh Sanyang, Omar Sey and Ansumana Sillah; DCD; Foma Ceesay, Seiko Suwareh and Alieu Tunkara. I wish to extend particular thanks to Kebba Lowe and Alieu Tunkara who were attached to the project. Kebba Lowe was not only responsible for approximately 20,000 eye examinations and 82 surgical operations conducted during the work but also for preliminary screening and the provision of medical care to study participants in the villages. I thank him for being 'ever ready' to go to work, for his punctuality, good humour and for sharing my enthusiasm for the project. Alieu Tunkara is another enthusiast for whom I have the greatest praise and admiration; he proved himself to be absolutely reliable, single-handedly conducting the masonry work and overseeing the construction of 596 of our 677 latrines serving 7,450 people - all without deviating from our exacting schedule. The research was supported by generous grants from the Department for International Development of the British Government and the Edna McConnell Clark Foundation. I am particularly grateful to Pene Key and Neil Squires at DfID and to Joe Cook and Jeff Mecaskey at EMCF for their personal interest, without which it would not have been possible to complete this work. The insecticide used was donated by Agrevo Environmental and I thank John Invest and John Goose for co-ordinating its safe delivery. Other thanks go to Madeleine Thomson for giving me the opportunity to get my vital first experience of practical field-based medical entomology; to an anonymous referee whose insightful comments greatly improved the literature review (Chapter 2); to David Mabey for his moral support and encouragement at every stage of the project; Linda Morison and Neal Alexander for statistical advice; and Amy Ratcliffe for discussion, statistical advice and proof reading drafts. This has been a community-based research project which has operated in 37 separate villages in the North Bank and Central River Divisions of The Gambia. I am indebted to the 8,600 residents of these villages who co-operated with interviews, attended for eye exams and allowed us free access to their homes. The enthusiastic participation of these people allowed this project to take place and often inspired us to keep going. I dedicate this thesis to my parents Ron and Beryl Emerson; wife. Amy Ratcliffe; and daughter, Charlotte Emerson, in recognition of their bountiful support and encouragement. In particular I thank my parents for indulging me as a 'perpetual student' and hope that they can feel proud to see their investment reach this point. Table of contents Title page 1 Abstract 2 Acknowledgements 3 Table of contents 5 List of tables 6 List of figures 8 List of abbreviations 10 Declarations 11 Chapter 1: Background and introduction 13 Chapter 2: A review of the evidence base for the "P and "E" components 21 of the SAFE strategy for trachoma control Chapter 3: Pilot study on the effect of fly control on trachoma 45 transmission and childhood diarrhoea Chapter 4: Transmission ecology of the fly Musca sorbens, a putative 55 vector of trachoma Chapter 5: Human and other faeces as breeding media of the trachoma 71 vector Musca sorbens Chapter 6: The Flies and Eyes Project. Design and methods of a 84 cluster-randomised intervention study to confirm the importance of flies as trachoma vectors in The Gambia and to test a sustainable method of fly control using pit latrines Chapter 7: Effect of fly spraying and pit latrines on trachoma 98 transmission in The Gambia: results of the Flies and Eyes project Chapter 8: The wider context: How knowledge of the ecology and control 119 of Musca sorbens relates to trachoma control References 128 List of tabOes Table Title Page 2.1 Literature providing evidence for the F and E components of 32 the SAFE strategy for trachoma control 3.1 Selected characteristics of the four pilot study villages 51 4.1 Background trachoma prevalence by age in the study area of 63 The Gambia (1997) 4.2 Species and sex distribution of eye-seeking flies caught from 65 Gambian children (1997-1998) 5.1 Production of Musca sorbens from trial breeding media: 77 Actual number of flies/stool (flies/Kg of medium) 5.2 Summary statistics of mean head-widths of Musca sorbens 79 caught from the eyes of children compared to those emerging from the breeding media 5.3 Air temperatures and development time of Musca sorbens by 80 trial 7.1 Crude results of baseline trachoma survey using the World 104 Health Organization Simplified Grading System for 6087 study participants seen in both surveys 7.2 Multivariate model of individual and household level risk 106 factors predicting active trachoma at baseline adjusted for clustering by household 7.3 Multivariate model of main daily activity and risk of active 107 trachoma for 1507 children aged 5-15 years adjusted for household clustering 7.4 Species and sex of flies caught in 2009 hand-net collections 109 of flies from children's faces 7.5 Adjusted geometric mean number of M.
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