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.

The matrix metalloproteinases family (MMPs) are proteins related to tumor formation and metastasis that have attracted the attention of scholars in recent years. Tumor cells can secrete MMPs during malignant transformation, and the expression of MMPs in different malignant tumors is diverse, and different members of MMPs do not have exactly the same biological properties. Matrix metalloproteinase-19 (MMP-19) is a new member of MMPs whose secretion increases rapidly during the malignant transformation of cells and is released into the extracellular space to participate in biological processes such as proliferation, adhesion, invasion, migration, and angiogenesis of tumor cells. In this paper, the progress of research on the biological properties of MMP-19 in tumors was reviewed to provide a theoretical basis for exploring the development of tumors, especially for studying the invasion and metastasis of tumor cells.