CIRCADIAN-RHYTHMS IN THE CERCARIAL EMERGENCE OF SCHISTOSOMA-MANSONI BY BIOMPHALARIA-TENAGOPHILA AT OUTDOORS - A COMPARATIVE-STUDY WITH BIOMPHALARIA-GLABRATA

Circadian rhythms in the emergence of S. mansoni cercariae from Biomph alaria tenagophila and B. glabrata, snail hosts of schistosomosis in B razil, were investigated. A total of 35 specimens of B. tenagophila(Sa o Paulo, Brazil) and 12 B, glabrata (Minas Gerais, Brazil) exposed ind ividually to five miracidia of Schistosoma mansoni originated from the same biotope as their snail hosts, were tested, Observations were car ried out at outdoors, with the quantification of cercarial emergence a t 3h intervals during three consecutive days in November 1989 and in M ay 1990. Cercarial emergence was essentially diurnal(from 06.00-18.00h ) in both species. Circadian rhythms were detected by the Single Cosin or Method among 74.3% of B. tenagophila and 91.7% of B. glabrata snail s. The acrophases corresponding to individual snails were between 11.3 7 e 17.54h in B. tenagophila and between 14.15 and 16.29h in B, glabra ta. These findings confirm our preliminary observations in B. tenagoph ila and are in accordance to those of other authors in regard to B, gl abrata. The acrophases of individual snails were similar within each s pecies, thus indicating that at populacional level cercarial emergence was concentrated in particular times of the day. Group acrophases for each species varied from 13.22 to 15.22h and were not significantly d ifferent between B, tenagophila and B, glabrata. Cercariae emerging fr om B, tenagophila snails seemed to be more sensitive to environmental temperature than those emerging from B. glabrata, at least in the temp erature range prevailing along the tests. Further chronobiological stu dies on host-parasite interactions are encouraged to improve our knowl edge about temporal aspects of schistosomosis transmission.