Studies on Schistosoma japonicum infection in the Philippines. 2. The molluscan host

Abstract

This study of the molluscan host (Oncomelania quadrasi) of bilharziasis in the Philippines is divided into two parts, the first dealing with the biology of the host and the second with the interrelationship between the host and Schistosoma japonicum.In the first part, the snail's distribution and habitat are considered in some detail, and then field and laboratory studies on its behaviour and activity are reported on. A section on the life history of O. quadrasi covers its growth, reproduction, egg-laying and survival. This is followed by a study of the population dynamics of the snail.In the second part, the laboratory procedures used for infecting snails and for obtaining cercariae are described, and the finding that more female than male snails are seen infected is discussed. A section is devoted to the effect of infection on the reproduction, growth and longevity of the snail, and an account is given of cercarial output, of the distribution of cercariae in a snail colony and of their presence downstream from snail colonies. The final section deals with natural fluctuations in snail infection rates, which appear to show a cycle related to rainfall.