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Divergent Effects of Schistosoma haematobium Exposure on Intermediate-Host Snail Species Bulinus nasutus and Bulinus globosus from Coastal Kenya

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  • 1 Division of Vector Borne Diseases, Ministry of Health, Nairobi, Kenya.
  • | 2 Center for Global Health and Diseases, Case Western Reserve University School of Medicine, Cleveland, Ohio.

Schistosoma haematobium infection causes urogenital schistosomiasis, a chronic inflammatory disease that is highly prevalent in many parts of sub-Saharan Africa. Bulinid snails are the obligate intermediate hosts in the transmission of this parasite. In the present study, Bulinus globosus and Bulinus nasutus snails from coastal Kenya were raised in the laboratory and exposed to miracidia derived from sympatric S. haematobium specimens to assess the species-specific impact of parasite contact and infection. The snails' subsequent patterns of survival, cercarial shedding, and reproduction were monitored for up to 3 months postexposure. Schistosoma haematobium exposure significantly decreased the survival of B. globosus, but not of B. nasutus. Although both species were capable of transmitting S. haematobium, the B. globosus study population had a greater cumulative incidence of cercarial shedders and a higher average number of cercariae shed per snail than did the B. nasutus population. The effects of prior parasite exposure on snail reproduction were different between the two species. These included more numerous production of egg masses by exposed B. nasutus (as compared with unexposed snails), contrasted to decreased overall egg mass production by parasite-exposed B. globosus. The interspecies differences in the response to and transmission of S. haematobium reflect clear differences in life histories for the two bulinid species when they interact with the parasite, which should be taken into account when planning control interventions aimed at reducing each host snails' contribution to local transmission of Schistosoma infection.

Author Notes

* Address correspondence to Charles H. King, Center for Global Health and Diseases, Case Western Reserve University School of Medicine, BRB Room 422, 2109 Adelbert Road, Cleveland, OH 44106. E-mail: chk@cwru.edu

Financial support: This research was supported by the National Institute of Allergy and Infectious Diseases and the Fogarty International Center of the U.S. National Institute of Health under Grants AI45473 (NIAID) and TW/ES01543 (Fogarty International Center).

Authors' addresses: H. Curtis Kariuki, School of Medicine and Health Sciences, Kenya Methodist University, Meru, Kenya, E-mail: hckariuki@yahoo.com. Julianne A. Ivy and Charles H. King, Center for Global Health and Diseases, Case Western Reserve University School of Medicine, Cleveland, OH, E-mails: jai24@case.edu and chk@cwru.edu. Eric M. Muchiri, Meru University of Science and Technology, Meru, Kenya, E-mail: ericmmuchiri@gmail.com. Laura J. Sutherland, Ohio State University College of Veterinary Medicine, Columbus, OH, E-mail: sutherland.93@osu.edu.

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