Development of larval Schistosoma japonicum blocked in Oncomelania hupensis by pre-infection with larval Exorchis sp.

Schistosomiasis continues to be a significant public health threat in the world. In the area of parasitic diseases, it is widely considered second only to malaria as a global health problem, with an incalculable drain on the economic resources of countries where it is endemic. Schistosoma japonicum is widespread in eastern and southeastern Asia, where the amphibious snail, Oncomelania hupensis, is the intermediate host. In the present study, we found that infection of O. hupensis with the mature eggs of another trematode, Exorchis sp., inhibited development of S. japonicum mother sporocysts in O. hupensis. Exorchis sp. commonly infects the edible fish Parasilurus asotus in China, but it is harmless to humans. This discovery provides an opportunity for possible biological control of S. japonicum infection and transmission. Additionally, it has the potential to substantially reduce the impact of the global S. japonicum that is independent of antihelminthic use. The mechanisms used by Exorchis sp. to inhibit infection by S. japonicum in the snail require further investigation.