Effect of Mass Chemotherapy and Piped Water on Numbers of Schistosoma Haematobium and Prevalence in Bulinus Globosus in Kwale, Kenya

Shinichi Noda Department of Medical Zoology, Faculty of Medicine, Kagoshima University, Kagoshima 890, Japan

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Masaaki Shimada Department of Parasitology, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852, Japan

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Katsuyuki Sato Department of Parasitology, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852, Japan

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John H. Ouma Division of Vector Borne Diseases, Ministry of Health, Nairobi, Kenya

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Fredrick W. Thiongo Division of Vector Borne Diseases, Ministry of Health, Nairobi, Kenya

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Ngethe D. Muhoho Centre for Microbiology Research, Kenya Medical Research Institute, Ministry of Health, Nairobi, Kenya

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Atsuo Sato Department of Medical Zoology, Faculty of Medicine, Kagoshima University, Kagoshima 890, Japan

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Yoshiki Aoki Department of Parasitology, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852, Japan

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From June 1982 to May 1986 in a small village in Kwale, Kenya, we studied seasonal fluctuations in populations of Bulinus globosus, prevalence of Schistosoma haematobium infection in this snail, and effects of chemotherapy and piped water supply on infection rate of snails. In the perennially-flowing Pemba River, relatively small numbers of snails were collected; they were found only during the hot dry season (December to March). In a tributary stream, the Kadingo River, whose flow ceased at the end of both the cool and hot dry seasons, snail numbers peaked at the end of the cool dry season (October to November) and at the beginning of the hot dry season (January). Large numbers of infected snails were found in the Kadingo River from November to January (short rainy season and beginning of dry season). Selective mass chemotherapy with metrifonate and provision of piped water were begun in February and March 1984. These control measures achieved a significant reduction in the infection rate of snails (P < 0.001); the annual infection rate for the 2 years before treatment was 9.3% and 13.1%, and for the 2 years after treatment was 3.5% and 3.4%.

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