Studies on the susceptibility of new Taiwan foci of Oncomelania hupensis to Ilan and Japanese strains of Schistosoma japonicum.

Sixty snails from four new foci of O. hupensis in Taitung, Chiayi, Hualien and Nantou counties, and 4 known colonies of O. h. chiui in Alilao and Pali in Taipei as well as of O. h. formosana in Changhua and Ilan on Taiwan were exposed each to 5 miracidia of Ilan zoophilic strain and Japanese anthropophilic or human strain of S. japonicum. This is the first report to note that all four new foci of O. hupensis snails were highly susceptible to Ilan strain of S. japonicum (17-20%). Susceptibility to the Japanese strain was detected in Taitung (33%), but, very low to not susceptible for the Hualien (2%), Chiayi and Nantou snails. Susceptibility of new Taiwan foci to the geographic strains of S. japonicum has now been well established, widespread distribution of susceptible snails in Taiwan could possibly lead to public health problem in the event that S. japonicum were introduced to the island.

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

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.