Studies on the Host-Parasite Relationship between Schistosoma Mansoni and the Snail Australorbis Glabratus

Chia-Tung PanDepartment of Tropical Public Health, Harvard School of Public Health, Boston, Massachusetts

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The host-parasite relationship between Schistosoma mansoni and the snail Australorbis glabratus has been studied in aquarium-reared (unsterile) and bacteriologically sterile snails. Detailed observations on the sites of development, routes of migration, and normal and abnormal histology of the parasite, and on the pathologic changes produced in the host, as seen in serial sections of snails fixed at various intervals after infection, showed these to be similar in snails of both types. By comparison with normal controls, it has been found that infection of aquarium-reared snails suppresses fecundity, that an acceleration of shell growth appears before the parasite matures, and that an eventual stunting of shell growth and a high mortality coincides with the period of heavy cercarial emergence and the appearance of intense host tissue reactions.

From observations on the development of the parasite in relation to tissue changes and mortality among infected snails, it is concluded that the extensive migration of large numbers of cercariae, and the intense tissue reactions associated with trapped degenerating cercariae, are important factors in causing death of the snails. Regeneration of exhausted daughter sporocysts may contribute to the release of cercariae for periods of several months from surviving snails.