Objective To investigate the ecological habit and characteristics of Trichobilharzia cercariae in the Huaihe river system. Methods During June of 2002-May of 2003, Radix auricularia snails were collected monthly in Yaohe Fishery of the branch of the Huaihe River. The cercariae, released from the positive snails and collected by Shade Drop Bottle, were examined by direct press. Ducklings were infected by cercariae with different ages and examined for the infection by miracidia hatching method.Results The results showed a typical seasonal fluctuation in infection rate of the snails, i.e. the cercariae detection rate was 0.81% in July, 0.65% in June, 0.07%-0.26% in April, May, August, September and October respectively, with a significant difference (? 2=26.73, P

F0.01(1,5)=16. 30,P0. 05). Conclusion Laboratory results thus suggest that infection intensity is related to snail size per se, whereas prevalence in the field is related to snail size only through the correlation between size and age. In addition, under these experimental conditions, infected snails were no larger than uninfected snails, so the gigantism snails observed in the field might not be attributable to Trichobilharzia-induced effect.

Gastric cancer is a malignant tumor with worldwide high incidence and threatening the human health severely. It is a disease induced by multiple factors. Exosomes play an important role in the pathogenesis and development of many malignant tumors including gastric cancer. Exosomes can transport specific contents to regulate local and distant cell communications, and are able to promote or inhibit the development of gastric cancer through regulating the growth and proliferation of tumor cells, relevant immune function and angiogenesis of tumors. This article reviewed the effects of exosomes and their contents on the pathogenesis and development of gastric cancer.