The intermediate host of schistosoma japonicum in China

Abstract

The snail which acts as the intermediate host of Schistosoma japonicum in Japan has been known since 1913 to be Blanfordia nosophora. No intermediate host for the parasite has heretofore been described for China. We selected the endemic region about Soochow, in Kiangsu Province, for our search. Our method consisted of first finding a case of the disease and then hunting in the neighborhood of the patient's home for a snail somewhat similar to Blanfordia nosophora. On August 11, 1922, such a snail was found in large numbers on the shore of a small terminal canal near which many cases of schistosomiasis japonica resided. Examination of these snails by crushing their shells revealed a five per cent. infection with cercariae morphologically similar to that of Schistosoma japonicum. A mouse immersed in water containing these cercariae was found, thirty-one days later, to harbor adult forms of Schistosoma japonicum in the portal and mesenteric veins. Snails of this type were exposed to miracidia of Schistosoma japonicum and at intervals thereafter were killed, and showed in serial section the development of the sporocyst and cercaria forms of the parasite.

The snail which acts as the intermediate host of Schistosoma japonicum in the Soochow district is an operculate gasteropod averaging 6.4 mm. in length by 3.0 mm,. in breadth. Its shell is acuminate in form, has seven spirals, is dextrally coiled, is of dense consistency and has closely set ridges running perpendicular to the spiral groove of the shell. Its shell differs from that of Blanfordia nosophora in its greater density, its ribbed surface and its greater breadth in proportion to its length. These features place the Chinese intermediate host in a different genus from the Japanese host.