Development and Effects of Schistosoma japonicum (Trematoda) on its Intermediate Host, Oncomelania hupensis (Gastropoda)

BACKGROUND Trematodes belonging to the genus Schistosoma cause schistosomiasis. The relationship between schistosomes and their intermediate hosts varies among snails. This study investigated the effects of S. japonicum on its snail host, Oncomelania hupensis, and cercarial release rythmicity of S. japonicum and the effects of light on it. METHODS Seven groups of O. hupensis (n = 40 each) were exposed individually to 0 (control), 2, 4, 6, 10, 15, and 20 S. japonicum miracidia. Mortality of the snails was recorded for 10 weeks. Snails in each group were checked for infection at seven weeks post-exposure. Positive snails were exposed to artificial light from 06:00 am - 18:00 pm and the liberated cercariae were collected every 2 hours to determine the rhythmicity of cercarial release. Three groups of positive snails (n = 6 each) were exposed to artificial light, daylight, and darkness from 06:00 am - 18:00 pm, the liberated cercariae were collected every 2 hours to determine the effects of light. RESULTS The highest infection rate and host mortality occurred among snails in the groups exposed to 15 and 20 miracidia. Cercariae were liberated after eight weeks of exposure of O. hupensis to S. japonicum. The circarial emerging pattern was circadian, with a single peak of emerging between 10:00 am and 12:00 pm. Light intensity had a positive influence on cercariae shedding and rhythmicity. CONCLUSION Further research, including the influence of biotic and abiotic factors is deemed necessary to fine-tune elucidation of the effects of S. japonicum upon O. hupensis snail.