Effect of Some Algal Species on the Snail Intermediate Hosts of Schistosomiasis in Egypt I. Survival, Fecundity and Net Reproductive Rates

Planktonic samples were collected from two habitats in Giza Governorate, Kafr Hakem (+ snails) and Sadek canals (snails). Oscillatoria accuminata and Lyngbya perelegans were collected from the first location, while Phormidium valderianum, Spirogyra sp and Lyngbya perelegans were separated from the second one. Nostoc muscorum was obtained from Theodor Bilharz Research Institute (TBRI) and used in some experiments as control because it is non toxic. The effect of the previously mentioned algal species on Biomphalaria alexandrina and Bulinus truncatus snails, the intermediate hosts of schistosomiasis in Egypt, was studied. Investigations were carried out on the survivorship (Lx), fecundity (Mx) and reproduction (R0) of the snails. The obtained results indicate that O. accuminata, Spirogyra sp and L. perelegans were non toxic, while P. valderianum was toxic to the two snail species (sublethal concentration LC0 was used in the experiments). Concerning the survivorship, both snail species fed on O. accuminata had a higher survival rate than snails fed on other algal species or lettuce. While low survival rate was recorded in both snail species fed on Spirogyra sp. Fecundity of snails fed on lettuce (control) showed the highest value, followed by P. valderianum and L. perelegans, while the lower fecundity value was recorded in snails fed on O. accuminata. Concerning the net reproductive rate, snails nourished on lettuce recorded the highest value, while those fed on L. perelegans showed the lowest one. Chromatographic analysis of P. valderianum extract (using GC/MS) revealed the presence of toxic and molluscicidaly active components.