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 individ ually exposed to one, two, or five miracidia of Schistosoma haematobiu m to assess how the quantity of miracidia would affect the shedding of cercariae. The infection rate of snails increased as the number of mi racidia increased (from 17% to 87% at 24-26 degrees C). The prepatent period was significantly shorter in planorbids exposed to a single mir acidium (38 days) than in the two groups infected with two or five mir acidia per snail (51-53 days). No significant difference was noted bet ween the mean values recorded for the three groups in terms of the pat ent-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 detect ed in the daily production of cercariae from P. metidjensis; however, its periodicity differed according to the snail group (15-16, 20-23, a nd 25-27 days for the groups infected with one, two, and five miracidi a, respectively.