Host choice and penetration bySchistosoma haematobiummiracidia

Abstract

AbstractSchistosome parasites commonly show specificity to their intermediate mollusc hosts and the degree of specificity can vary between parasite strains and geographical location. Here the role of miracidial behaviour in host specificity ofSchistosoma haematobiumon the islands of Zanzibar is investigated. In choice-chamber experiments,S. haematobiummiracidia moved towardsBulinus globosussnail hosts in preference to empty chambers. In addition, miracidia preferred uninfected over patentB. globosus. This preference should benefit the parasite as patent snails are likely to have mounted an immune response toS. haematobiumas well as providing poorer resources than uninfected snails. Miracidia also discriminated between the hostB. globosusand the sympatric, non-host speciesCleopatra ferruginea. In contrast,S. haematobiumdid not discriminate against the allopatricBulinus nasutus. Penetration of the host by miracidia was investigated by screening snails 24 h after exposure using polymerase chain reaction (PCR) withS. haematobiumspecificDraI repeat primers. There was no difference in the frequency of penetration ofB. globosusversusB. nasutus. These responses to different snail species may reflect selection pressure to avoid sympatric non-hosts which represent a transmission dead end. The distribution ofB. nasutuson Unguja is outside the endemic zone and so there is less chance of exposure toS. haematobium, hence there will be little selection pressure to avoid this non-host snail.