The infectivity and pathogenicity of geographical strains of Schistosoma mansoni

Abstract

The characteristics of 4 strains of Schistosoma mansoni from Egypt, Puerto Rico and Tanzania have been studied in albino mice and golden hamsters. The prepatent period of a particular strain was shorter in hamsters than in mice, and significant differences were demonstrated between the duration of the prepatent periods of the various strains in the same host. The prepatent period of a recently isolated Puerto Rican strain of S. mansoni was not significantly different from that of a strain isolated from the same locality and maintained for some years in the laboratory. The Egyptian and Puerto Rican strains were more infective to mice than the Wellcome and Mwanza strains. Judging by the longevity of mice after exposure to the same number of cercariae, the virulence of the Wellcome strain was the highest and that of the Mwanza the lowest, with the Puerto Rican and Egyptian strains in between. Intestinal haemorrhages were more frequent in mice infected with the more virulent strains. The Puerto Rican strain produced significantly more eggs in the visceral organs of albino mice than the Mwanza strain. In hamsters the Puerto Rican strain also produced the highest number of eggs, and the Egyptian strain produced the lowest. The percentage distribution of S. mansoni eggs in mice and hamsters was shown to be influenced by the strain of the parasite and the species of the host. The importance of these infra-specific variations in relation to the epidemiology and pattern of pathogenicity of S. mansoni infections in different endemic areas is discussed.