The pattern of emergence of O. viverrini cercariae
from infected B. (D.) s. goniomphalos under natural
conditions showed clear diurnal periodicity. The snails
started shedding cercariae between 6:00-8:00 AM
through 8:00 PM after which the emergences werestrictly suppressed until 6:00 AM The peak emergence
was between 8:00-10:00 AM. The same pattern was
observed on the next day (Fig 1; Table 1).