[Changes of historical Paragonimus metacercaria infection rates of freshwater crabs in Yongjia County].

Objective: To understand the changes of Paragonimus metacercaria infection rates of freshwater crabs in Paragonimus endemic areas and explore the causes in Yongjia County, Zhejiang Province, China.

Methods: A field investigation was carried out. The freshwater crabs were collected and the metacercaria were separated from the crabs. The infection rates, infectiosities and infection indexes were calculated and the results were vertically compared with the historical findings. The causes of the changes were discussed.

Results: Compared with those in 1980, the average infection rate in original endemic areas decreased from 59.71% to 21.50% (P < 0.05), while the infection density decreased from 1.09/g to 0.23/g (P < 0.05). The infection index decreased obviously. In Hesheng Village, it decreased from 4.05 to 0.01 (P < 0.01), in Wuchi Village, it was from 37.90 to 2.91 (P <0.01), and in Daruoyan Scinic area,it was from 5.85 to 0.03 (P < 0.01). Two endemic areas disappeared but two new endemic areas (Sihai Village and Sunshan Village) were found, and in Sunshan Village, the metacercaria infection rate was 100%, the infection density and infection index were 21.30/g and 3 402.68 respectively, which meant it was a super high endemic focus.

Conclusion: The Paragonimus metacercaria infection rate in crabs is lower than before in Yongjia County, but some super high epidemic focus of paragonimiasis still exists. Therefore, we still should strengthen the control measures.