RESUMO
This study was monthly done for one year in small agricultural area in Behaira Governorate. Thirty permanent stations were chosen along primary, secondary and tertiary canals and drains, 5 stations for each. In the area of study, Biomphalaria alexandrina [B. alexandrina] snails were more prevalent than Bulinus truncatus [B. truncatus] snails, although the percentage of infected B. truncatus with different trematodes was 12 times the percentage of infected B. alexandrina snails. These two snail species of schistosomiasis were more dense from March until August during the year of study. B. alexandrina and B. truncatus seemed to be ideal intermediate hosts for holostome cercariae [about 55% of the total infected snails with different trematodes]. Schistosome was the second prevalent cercariae as well as amphistome, xiphidiocercariae, echinostome and monostome. Nevertheless, echinostome was the second prevalent cercariae in B. truncatus, in addition to amphistome, monostome and xiphidiocercariae but not schistosome cercariae. Old size snails of both kinds of schistosomiasis had a higher rate of infection with different trematodes cercariae, then medium followed by young size snails. Schistosoma mansoni [S. mansoni] cercariae were found only in old and medium size B. alexandrina snails. The highest infection with different trematodes larvae among the collected B. alexandrina snails was recorded in secondary and tertiary canals and drains, while for B. truncatus snails it was in primary and secondary canals. Also, the infected B. alexandrina snails with S. mansoni was found only in secondary and tertiary canals and drains. Conclusively, infection of both snails of schistosomiasis with different trematodes, suppress in one way or another the infection with S. mansoni and S. hematobium larvae. Suggestions of using these kinds of trematodes infection for biological control if the snails intermediate hosts of schistosomiasis were discussed