Irrigation and Malaria in Africa
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Durham E-Theses The impact of bund construction on the transmission of malaria in The Gambia Kandeh, Balla How to cite: Kandeh, Balla (2007) The impact of bund construction on the transmission of malaria in The Gambia, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/2380/ 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 The impact of bund construction on the transmission of malaria in The Gambia Balla Kandeh School of Biological and Biomedical Sciences Durham University The copyright of this thesis rests with the author or the university to which it was submitted. No quotation from it, or information derived from it may be published without the prior written consent of the author or university, and any information derived from it should be acknowledged. A thesis submitted for the award of the Degree of Masters of Science (by Research) September 2007 1 5 MAY 2008 Executive Summary Water impoundments are known to affect the risk of many vector-borne diseases. Here I examine the impact of bund (smal'l embankments) construction on the transmission of malaria in The Gambia. I hwothesised that bund construction, designed to collect rainwater for irrigation and keeping saltwater out, would provide ideal breeding sites for Anopheles gambiae mosquitoes, the major vectors of malaria in Afiti.ca, and thereby increase malaria transmission. Mosquito larvae were sampled along transects in three different areas~ Each transect lay perpendicular to a bund, including an area 1OOm either side of the bund. These were sampled for larvae using area samplers every three weeks from May to December 2005, including the period of annual rainfall from June to October. Adult mosquitoes were caught using three emergence traps which were positioned at each side of the bund in different water bodies (i.e. six at each transect, three either side of the hunds), within 50m left and right of each transect. During a Countrywide survey, 20 transects were sampled in different parts of The Gambia in September 2005, when mosquito numbers were relatively high. 10 were situated in parts of the river where it was salt and 10 were situated in parts of the river where the water was fresh. Mosquitoes were roughly twice as common in water on the landward side of the bunds, 68% of Anopheles larvae and 84% of all mosquito larvae, (OR)= 9.37, 95% confidence intervals (95% Cis = 2.26-38.79, P <0.002), compared with the riverside. Similarly 82% of Anopheline adults and 89% of all adult mosquitoes (OR = 2.59, 95% Cis = 1.23-5.48, P = 0.013) were collected on the landward side. There is also an indication that this is also true for the countrywide survey in which more mosquitoes were collected from the landside of the bund (63% Anophelines, 65% Culicines), although this did not reach statistical significance. One possible explanation for these fmdings is that larvae on the riverside of the bunds are washed away with the tide and predated by the larger number of fish found there. These fmdings indicate that the construction of bunds for agricultural purposes increases mosquito larval density on the landward side by increasing the breeding ground for malaria vectors of the An. gambiae complex. These constructions increase the number of vector mosquitoes emerging from 2 the floodplains of the River Gambia, and thus are likely to increase the intensity of malaria transmission. 3 Declaration The material contained within this thesis has not been previously submitted for a degree at Durham University of or any other Institution. The research reported in this thesis has been conducted entirely by the author unless indicated otherwise. The copyright of this thesis rests with the author. No quotation from it should be published nor any methodology implemented without the prior consent of the author. Any information derived from this thesis should be appropriately acknowledged. Contributions of Other Authors Prof. S. W. Lindsay (Supervisor) conceived the design of the study, identified the study sites, helped in the field work, assisted in the data analysis, critiqued and reviewed the manuscript. Dr Urike Fillinger, helped develop the Standard Operational Procedures (SOPs). Silas Majambereh, helped identify study sites, and also assisted in the field work. Dr Clare Green helped with the molecular analysis of specimens. Vasilis Louca, PhD student and fish ecologist, helped with the fish sampling, identification and measurement of fish samples. 4 Dedication This piece of work is dedicated entirely to my late mother Mts Jainabou Baldeh Kandeh who died in 1968 shortly after I was born. I miss you dearly. May your soul rest in perfect peace. Amen. 5 Acknowledgements I would like to thank my supervisor Professor Steve Lindsay, Mr Silas Majambereh, Dr Ulrike Fillinger, Dr Clare Green and Dr Matthew Kirby, who gave me excellent theoretical and practical support during the entire process. Without their support, it would not have been possible to achieve the diversity of studies that have been conducted during this project. I also wish to sincerely thank the Nlli, USA, for providing me with the funding through the Larval Control Project (LCP) in The Gambia. I also wish to thank the Medical Research Council Laboratories in The Gambia for providing excellent laboratory facilities throughout the study period. In addition, I thank the Department of State for Health and the Government of The Gambia for according me w:ith this training opportunity without which, I would not have successfully completed. Thank you so much Mr Malang Fofana and Mrs Adam Jagne Sonko Manager and Deputy manager of the NMCP and the entire staff of the NMCP for all your moral, material and technical support and encouragement during the course of my study, for without your support it would have been difficult for me to complete successfully. I would particularly like to thank all the personnel of the MRC Farafenni in The Gambia who made this project possible. Special thanks to Mr Musa Jawara, Batch Cham, Wandifa Fofana, Lamin Sanneh, Essa Touray, Tomaring Jadama, Ebriama Manneh, Ousman :Bah, Lamin Sanyang, Abdoulie Bojang, Alagie, Nyamo, Mr Nyassi and Pierre Gomez. I would also like to thank Dr Jassey and Mr Batch Cham for their immense help during the conduct of the study. Last but not in anyway the least, special thanks to my dear wife Mrs Binta Sallah Kandeh most especially for a.ll your support and encouragement during the course of my study. 'Fhank you so much Binta Sallah for taking good care of my famHy while I was away. Thanks to my son Abdourahman Kandeh for your understanding and patience during my absence. 6 Table of contents EXECUTIVE SUMMARY .......................................................................................................................2 DECLARA:riON ........................................................................................................................................4 DEDICATION............................................................................................................................................ S ACKNOWbEDGEMENTS....................................................................................................................... 6 TABLE OF CONTENTS ..........................................................................................................................7 LIST OF ACRONYMS ............................................................................................................................9 LIST OF FIGURES ................................................................................................................................10 LIST OF TABLES ...................................................................................................................................11 LIST OF·TABLES .................................................................................................................................... l:l CHAPTER 1: IRRIGATION AND MALARIA IN AFRICA .................................................... 12 POPULA7JlON GROWTH AND 'FOOD PRODUCTION IN AFRICA ............................................................... 12 RICE PRODtiCTION AND CONSUMPTION ................................................................................................ 14 IRRIGATION AND HEALTH ....................................................................................................................... 15 RICE CULTIVATION AND MALARIA ......................................................................................................... 15 IN AFRICA, RICE ...................................................................................................................................... 15 THE GAMBIA ...........................................................................................................................................