Emergence of Opisthorchis viverrini cercariae from naturally infected Bithynia (Digoniostoma) siamensis goniomphalos.

Under natural conditions, the emergence of Opisthorchis viverrini cercariae from naturally infected Bithynia (Digoniostoma) siamensis goniomphalos showed diurnal periodicity, peaking between 8:00-10:00 AM. The cercariae did not emerge during darkness, but low-intensity light could induce a release. Cercariae shedded from each field infected B.(D.) s. goniomphalos was recorded daily. The maximum output from one snail was 1,728 cercariae in a day. The total cercarial output from all five infected snails was 56,555 and the maximum of total cercariae shed from one snail was 27,692. The field-infected B. (D.) s. goniomphalos could survive for 70 days after the snails were collected.