Schistosoma haematobium: influence of the number of miracidia on several characteristics of infection in newborn Planorbarius metidjensis.

Newborn Planorbarius metidjensis (less than 72 h of life) were individually exposed to one, two, or five miracidia of Schistosoma haematobium to assess how the quantity of miracidia would affect the shedding of cercariae. The infection rate of snails increased as the number of miracidia increased (from 17% to 87% at 24-26 degrees C). The prepatent period was significantly shorter in planorbids exposed to a single miracidium (38 days) than in the two groups infected with two or five miracidia per snail (51-53 days). No significant difference was noted between the mean values recorded for the three groups in terms of the patent-period duration (48-70 days), the total number of cercariae (1,570-1,935/snail), and size at snail death (5.4-6 mm). A rhythm was detected in the daily production of cercariae from P. metidjensis; however, its periodicity differed according to the snail group (15-16, 20-23, and 25-27 days for the groups infected with one, two, and five miracidia, respectively.