Mekong schistosomiasis: I. Life cycle of Schistosoma japonicum, Mekong strain in the laboratory

Abstract

The occurrence of schistosomiasis in populations living along certain parts of the Lower Mekong River has been well documented. Snails of the genus Oncomelania, which are the intermediate hosts of human schistosomes in China, Japan, and the Philippines, are not found in continental Southeast Asia. The search for an alternative intermediate host for the Mekong schistosome has been undertaken by a number of investigators. Initial success in this endeavour was achieved in 1972, when Harinasuta et al., demonstrated that a hydrobiid snail, Lithoglyphopsis aperta Temcharoen, 1971, was experimentally capable of transmitting the disease. The strain which morphologically resembles S. japonicum in the adult stage and which infects humans and dogs on Khong Island, southern Laos, is able to complete its life cycle in L. aperta. Of 68 surviving exposed snails, 20 shed cercariae following en masse exposure to miracidia from dogs. Cercariae emerged naturally as early as 45 days after miracidial penetration. Mice, dogs, hamsters and rabbits were infected experimentally. Prepatent periods ranged from 43 to 49 days in mice, dogs and hamsters. Adult worms were recovered from rabbits but eggs were not seen in their faeces.