Further studies on the susceptibility of new Taiwan foci of Oncomelania hupensis to geographic strains of Schistosoma japonicum.

ABSTRACT

Two known colonies of O.h chiui in Alilao and of O.h. formosana in Changhua and four new foci of snails in Nantou, Chiayi, Hualien and Taitung on Taiwan were exposed each to 5 miracidia of Changhua Zoophilic strain and Chinese, Philippine and Indonesian anthropopilic or human strains of S. Japonicum. The results showed that all four new foci demonstrated various degrees of susceptibility to this parasite. Infectivity of Chinese strain of S. japonicum in 4 new foci of snails is reported for the first time. Changhua race of O. hupensis was also found slightly susceptible to Chinese strain of the parasite. The average infection rate to both zoophilic and human strains of S. japonicum was 39.0%, 14.5%, 10.8% and 9.8% for Taitung, Chiayi, Hualien and Nantou snails respectively. Susceptible snails now been found in 7 counties and if by chance human pathogenic strains of the parasite were accidentally introduced into Taiwan, a public health problem could possibly develop.