Thirty-six macaques (29 from Formosa, 3 from Japan and 4 from the Philippines) were exposed to S. japonicum cercariae of three geographical strains (Formosan, Japanese and Philippine). The degree of susceptibility of the monkey species to the strains of the parasite was ascertained by the length of the prepatent period, the number of eggs produced, the immature-mature egg ratio, and the number of adult worms at autopsy.
The results of the experiments showed that the Formosan monkey was highly susceptible to the Japanese and Philippine strains but was a relatively poor host for the Formosan strain. On the other hand, the Philippine and Japanese monkeys made reasonably good hosts for the Formosan strain of the parasite. This indicates that the Formosan strain of S. japonicum differs from the Japanese and Philippine strains.