title: 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.
abstract: 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.
authors.affiliation: Kuvin Center, Hebrew University, Hadassah Medical School, Jerusalem, Israel. hambu@cc.huji.ac.il
authors.forename: Joseph
authors.initials: J
authors.lastname: Hamburger
authors.forename: Orit
authors.initials: O
authors.lastname: Hoffman
authors.forename: H Curtis
authors.initials: HC
authors.lastname: Kariuki
authors.forename: Eric M
authors.initials: EM
authors.lastname: Muchiri
authors.forename: John H
authors.initials: JH
authors.lastname: Ouma
authors.forename: Davy K
authors.initials: DK
authors.lastname: Koech
authors.forename: Robert F
authors.initials: RF
authors.lastname: Sturrock
authors.forename: Charles H
authors.initials: CH
authors.lastname: King
mesh_terms: D000818:Animals; D002033:Bulinus / Q000469:parasitology*; D016054:DNA, Protozoan / Q000032:analysis*; D004199:Disease Vectors; D007630:Kenya; D016133:Polymerase Chain Reaction / Q000379:methods*; D012548:Schistosoma haematobium / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D016054:DNA, Protozoan