Susceptibility of Oncomelania Hybrid Snails to Various Geographic Strains of Schistosoma Japonicum *

Abstract
The hybrids of four subspecies of Oncomelania hupensis were exposed to infection with miricidia of four strains of Schistosoma japonicum geographically related to the parent snails. The results permitted the postulation that when a strain of S. japonicum infects a snail, it will also usually develop in hybrids of which one snail parent is susceptible to infection. Oncomelania hupensis hupensis is susceptible to all strains of S. japonicum that infect man, while the Changhua race of Oncomelania hupensis formosana is susceptible only to the Formosan (zoophilic) strain of the parasite. However, hybrids of these snails served as intermediate hosts for both the human and the zoophilic strains of the parasite. Infected hybrid snails survived twice as long as infected unhybridized snails. A lower infection rate and later shedding of cercariae was observed in hybrids and snails infected with unnatural geographical strains than in snails infected with geographically related strains.

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