AJTMH Transactions of the Royal Society of Tropical Medicine and Hygiene
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Am. J. Trop. Med. Hyg., 70(1), 2004, pp. 63-71
Copyright © 2004 by The American Society of Tropical Medicine and Hygiene

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THE EFFECT OF REPEATED HALF-YEARLY DIETHYLCARBAMAZINE MASS TREATMENT ON WUCHERERIA BANCROFTI INFECTION AND TRANSMISSION IN TWO EAST AFRICAN COMMUNITIES WITH DIFFERENT LEVELS OF ENDEMICITY

PAUL E. SIMONSEN, DAN W. MEYROWITSCH, DUNSTAN A. MUKOKO, ERLING M. PEDERSEN, MWELE N. MALECELA-LAZARO, RWEHUMBIZA T. RWEGOSHORA, JOHN H. OUMA, NAFTAL MASESE, WALTER G. JAOKO, AND EDWIN MICHAEL
Danish Bilharziasis Laboratory, Charlottenlund, Denmark; Division of Vector Borne Diseases, Ministry of Health, Nairobi, Kenya; National Institute for Medical Research, Dar es Salaam, Tanzania; Department of Medical Microbiology, College of Health Sciences, Nairobi, Kenya; Department of Infectious Diseases Epidemiology, Imperial College School of Medicine, London, United Kingdom

The effect of repeated half-yearly mass treatment with diethylcarbamazine (DEC, 6 mg/kg body weight) on infection and transmission of Wuchereria bancrofti was assessed and compared in communities with high and low endemicity in eastern Africa, with pretreatment microfilaria (mf) and circulating filarial antigen (CFA) prevalences of 29.4% and 53.2% in the high endemicity community and 3.1% and 18.7% in the low endemicity community, respectively. Human infection was monitored by repeated cross-sectional surveys, and transmission by weekly light trap collection of vector mosquitoes in selected houses in each community. Treatments resulted in a progressive decrease in microfilaremia and circulating antigenemia in both communities, with relative reductions being considerably higher for mf than for CFA. Among pretreatment mf-positive individuals, more than 60% were diagnosed as mf negative and mean mf intensities were reduced by 99% in both communities after two treatment rounds. In contrast, only moderate reductions were seen in circulating antigenemia among pretreatment CFA-positive individuals, with mean intensities still being 24–39% of pretreatment values after two treatment rounds. Among the pretreatment mf/CFA-positive individuals, clearance to a CFA-negative status was negligible. Complete CFA clearance was only observed among pretreatment CFA-positive but mf negative individuals who also had much lower initial mean CFA levels than the mf-positive individuals. After treatment, the intensity of transmission decreased in the high-endemicity community, but this appeared mainly to be a consequence of a drought-induced reduction in vector density rather than to reduced mf load in the human population, since the proportion of mosquitoes carrying infective larvae was not reduced. No change in transmission or mosquito infectivity was observed after treatment in the low-endemicity community. Implications of these observations for the control of Bancroftian filariasis are discussed.

Received June 18, 2003. Accepted for publication September 18, 2003.

Acknowledgments: We are grateful for the dedicated and skilled technical assistance provided by the staff of the Bombo Field Station (Joyce Kivugo, Charles Guzo, Megumi Yamakawa, Stephen David, Sudi Hassani, Mwanaisha Mganga, Benjamin Chambika, Peter Mhina, Maembe Mzee, and Robert Reuben), the Msambweni Field Station (Anthony Chome, Charles Nganga, Jackson Mwandi, Kepha Otieno, and Samuel Biego), Masaika Village (Abdul Ndamungu, Edward Winston, Mussa Mohamed, and Saidi Yahaya) Kingwede Village (Josephat Muthoka, Hassan Kilalo, and Bakari Mwanguku) and the Danish Bilharziasis Laboratory (Pernille Lund Strøm).

Financial support: The study was supported by the Program of International Cooperation with Developing Countries (INCO-DC) of the Commission of the European Communities (contract no. ERBIC18CT970257), the Danish Bilharziasis Laboratory, Denmark, and the Medical Research Council, United Kingdom.

Authors’ addresses: Paul E. Simonsen and Erling M. Pedersen, Danish Bilharziasis Laboratory, Jaegersborg Alle 1 D, 2920 Charlottenlund, Denmark. Dan W. Meyrowitsch, Institute of Public Health, Department of Epidemiology, University of Copenhagen, Blegdamsvej 2, 2200 Copenhagen N, Denmark. Dunstan Mukoko, John H. Ouma, and Naftal Masese, Division of Vector Borne Diseases, Ministry of Health, PO Box 20750, Nairobi, Kenya. Mwele N. Malecela-Lazaro and Rwehumbisa T. Rwegoshora, National Institute for Medical Research, PO Box 9653, Dar es Salaam, Tanzania. Walter G. Jaoko, Department of Medical Microbiology, College of Health Sciences, PO Box 19676, Nairobi, Kenya. Edwin Michael, Department of Infectious Diseases Epidemiology, Imperial College School of Medicine, Norfolk Place, London W2 1PG, United Kingdom.

Reprint requests: Paul E. Simonsen, Danish Bilharziasis Laboratory, Jaegersborg Alle 1 D, 2920 Charlottenlund, Denmark, Telephone: 45-77-32-77-32, Fax: 45-77-32-77-33, E-mail: pes{at}bilharziasis.dk.






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