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Am. J. Trop. Med. Hyg., 71(6), 2004, pp. 765-773
Copyright © 2004 by The American Society of Tropical Medicine and Hygiene

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LARGE-SCALE, POLYMERASE CHAIN REACTION–BASED SURVEILLANCE OF SCHISTOSOMA HAEMATOBIUM DNA IN SNAILS FROM TRANSMISSION SITES IN COASTAL KENYA: A NEW TOOL FOR STUDYING THE DYNAMICS OF SNAIL INFECTION

JOSEPH HAMBURGER, ORIT HOFFMAN, H. CURTIS KARIUKI, ERIC M. MUCHIRI, JOHN H. OUMA, DAVY K. KOECH, ROBERT F. STURROCK, AND CHARLES H. KING
Kuvin Center, Hebrew University, Hadassah Medical School, Jerusalem, Israel; Division of Vector Borne Diseases, Ministry of Health, Nairobi, Kenya; Kenya Medical Research Institute, Nairobi, Kenya; London School of Hygiene and Tropical Medicine, London, United Kingdom; Center for Global Health and Diseases, Case Western Reserve University, School of Medicine, Cleveland, Ohio

Levels of prepatent Schistosoma haematobium infection were monitored in intermediate host snails (Bulinus nasutus) collected from transmission sites in coastal Kenya, using a polymerase chain reaction (PCR) assay amplifying the Dra I repeated sequence of S. haematobium. The timing and number of prepatent and patent infections were determined for each site and, where the time of first appearance was clear, the minimal prepatent period was estimated to be five weeks. High, persistent, prepatency rates (range = 28–54%), indicated a significant degree of repeated area contamination with parasite ova. In contrast, rates of cercarial shedding proved locally variable, and were either low (range = 0.14–3.4%) or altogether absent, indicating that only a small proportion of infected snails reach the stage of cercarial shedding. Given the apparently strong focal effects of environmental conditions, implications of these new data are discussed regarding the estimation of local force of transmission and the design of control activities.

Received February 15, 2004. Accepted for publication July 7, 2004.

Acknowledgments: We thank Peter Mungai for his invaluable managerial input, and Anthony Chome, Charles Nganga, Jackson Muinde, Robin Bundi, Idi Masemo, and Joyce Bongo for their invaluable contributions to the field work. Grace Nguma took care of data entry and management. This paper is published with the kind permission of the Director of Medical Services, Ministry of Health, Kenya. Joseph Hamburger wishes to thank Dr. Eli Meir for his assistance in facilitating the summary of the results. Portions of this work were performed in fulfillment of the Ph.D degree of Orit Hoffman.

Financial support: This research was supported by grants from the National Institutes of Health under grants AI-45473 (National Institute of Allergy and Infectious Diseases) and TW/ES01543 (Fogarty International Center).

Authors’ addresses: Joseph Hamburger and Orit Hoffman, Department of Parasitology, The Kuvin Center for the Study of Infectious and Tropical Diseases, Hebrew University of Jerusalem, Hadassah Medical School, PO Box 12272, Jerusalem, 91120, Israel, Telephone: 972-2-675-8082, Fax: 972-2-6757425, E-mails: hambu{at}cc.huji.ac.il and orirh{at}md2.huji.ac.il. H. Curtis Kariuki and Eric M. Muchiri, Ministry of Health, PO Box 20750, Nairobi, Kenya, Telephone: 254-20-725833, Fax: 254-20-720030, E-mail: schisto{at}wananchi.com. John H. Ouma and Davy K. Koech, Kenya Medical Research Institute, Mbagathi Road, Nairobi, Kenya, Telephone: 254-20-722541, Fax: 254-20-720030, E-mails: ouma{at}wananchi.com and dkoech{at}kemri.org. Robert F. Sturrock, 92 Brennard Road, Dongara, WA6525, Western Australia, Australia, Telephone: 61-08-9927-1556, E-mail: sturrock{at}iprimus.com.au. Charles H. King, Center for Global Health and Diseases, Wolstein 4126, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106-7286, Telephone: 216-368-4818, Fax: 216-368-4825, E-mail: chk{at}po.cwru.edu.




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I. ABBASI, C. H. KING, R. F. STURROCK, C. KARIUKI, E. MUCHIRI, and J. HAMBURGER
DIFFERENTIATION OF SCHISTOSOMA HAEMATOBIUM FROM RELATED SCHISTOSOMES BY PCR AMPLIFYING AN INTER-REPEAT SEQUENCE
Am J Trop Med Hyg, May 1, 2007; 76(5): 950 - 955.
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