[Epidemiological investigation on the intermediate hosts of Paragonimus in Ninghai County of Zhejiang Province].

Freshwater crabs and snails were collected from Ninghai County in Zhejiang Province, and examined respectively for Paragonimus metacercariae and cercariae. Among 97 freshwater crabs found, the prevalence was 11.3% (11/97) with a mean intensity of 1 metacercariae per crab. It was 10.2% (5/49) and 20.2% (4/20) in the groups weighted 5-15 g and 15-25 g respectively, with an average intensity of 1, and no metacercariae were found in weight group of 25-35 g. Two positive crabs were found from 20 crabs with a low weight (< 5 g). Male to female crabs ratio was 2.5:1, and there was no significant difference in prevalence between males [12.7%(7/55)] and females [9.1% (2/22)]. No cercariae or metacercariae were found in 200 snails (Semisulcospira libertino).