Abstract
A survey for the detection of Paragonimus ohirai metacercariae in brackish water crabs was carried out during the period from October 1982 to September 1985 in the six rivers in the Tokai district, central Japan. These rivers are the Ibi, Nagara, Kiso, Nikkou, Shin and Shounai river which flow into the Ise Bay between Aichi and Mie Prefectures. The brackish water crabs collected were of the species Sesarma dehaani, S. intermedia, Helice tridens and Chasmagnathus convexus. Paragonimus ohirai metacercariae were detected in the first two species. Metacercariae were detected in crabs collected at 17 out of 19 study sites which are situated from about 5.5 to 13.0 km from the estuaries of the Ibi, Nagara and Kiso rivers. The infection rate was 2.7-100 per cent for S. dehaani and 0.9-100 per cent for S. intermedia, while the average number of metacercariae per positive crab was 1.0-96.0 and 1.0-30.2, respectively. The infection rate was higher among the crabs collected from the twelve study sites situated about 6-11 km up from the estuaries of the three rivers. Although a survey done in 1958 reported that only two sites in the Nagara river were positive for crabs, the present study revealed that the infected areas were distributed widely along the three rivers. In the present survey, a new P. ohirai-infected area was found along the Shin river for the first time, despite only limited investigations in the other three rivers. No crabs with metacercariae were observed along the Nikkou river, where P. ohirai had been found in the past.
