Effects of physico-chemical factors on the infection of mice with Schistosoma japonicum and S. mekongi cercariae.

The three physico-chemical characteristics of water tested-pH, temperature and salinity were found to affect the infection of mice by cercariae of S. japonicum and S. mekongi. For both species of schistosomes, the range of optimal pH that showed highest infection and worm recovery rates was between 5.4-7.4 and decreased as the pH increased. Cercariae exposed to temperatures between 15 degrees-30 degrees C showed the highest infection and worm recovery rates. As temperature decreased or increased, the infection and worm recovery rates decreased. Sodium chloride concentration at low level (0.5-200 ppm) did not have great effect on the infection and worm recovery rates. The infection and worm recovery rates decreased as salinity increased. High sodium chloride concentration at 3200 ppm for S. mekongi cercariae and at 6400 ppm for S. japonicum cereariae inhibited cercarial penetration and no infection occurred.