Biology of Robertsiella kaporensis snails and Malaysian Schistosoma.

Studies on the bionomics and host-parasite relationship of Robertsiella kaporensis and Malaysian Schistosoma were investigated. The study was divided into 4 parts: cultivation of snails, R. kaporensis, and maintenance of Malaysian Schistosoma life cycle, daily cercarial shedding cycle in R. kaporensis, miracidial load and cercarial shedding pattern and the infectivity of Malaysian Schistosoma cercariae. R. kaporensis were cultured in the laboratory with the use of plastic container provided with fine sand. The snails were fed with diatoms and Saraca leaves. The development period for the snail eggs was about 20-30 days, the young grew to maturity in 14-15 weeks, and the average growth rate of snails was 0.23 mm per week. The daily cercarial shedding cycle of snails had shown that the peak emergence of cercariae of Malaysian Schistosoma occurred at night, between 6-10 pm. The miracidial load which yielded the best results in terms of percentage infection rates of snails and cercarial output was the miracidial concentration of 8 miracidia per snail. The study on infectivity of Malaysian Schistosoma cercariae has shown that there was a decrease in infectivity of the cercariae to mammalian hosts as the cercariae increased in age. The percentage infection rate of mice and numbers of worms recovered were highest in mice infected with cercariae of 0-1/2 hr. old. Infection of cercariae fell rapidly after the cercariae were 16 hr. old.

Effects of cercarial concentration and length of exposure on the infection of mice by Schistosoma japonicum and S. mekongi cercariae.

The effects of cercarial concentration and length of exposure on the infection of mice by Schistosoma japonicum and S. mekongi were studied under laboratory conditions. For all cercarial concentrations of 10, 20 and 30, mice exposed for 1 min acquired little or no infection. Total worm recovery tended to rise with an increase either in cercarial concentration or exposure time. The highest infection rate and worm burden were obtained in mice exposed for 64 min to 30 cercariae per mouse. The present investigation suggested that exposures of 1 min or less carried little risk of infection at low cercarial concentration. There was a greater risk of infection in prolonged exposure to low cercarial concentration. Prolonged exposures to high cercarial concentration carried the greatest risk of high infection rate and worm burden.