Histopathological and Ultrastructural Studies on Biomphalaria alexandrina Snails Infected with Schistosoma mansoni miracidia and Treated with Plant Extracts

Background: Biomphalaria alexandrina snails are the intermediate host of Schistosoma mansoni in Egypt. Aim of the work: this study aimed  to evaluate the molluscicidal activity of the methanol extract of the plants Anagallis arvensis and Viburnum tinus against B. alexandrina (Normal and S. mansoni infected). Results: the present results proved high activity for both plant extracts (LC₅₀ & LC₉₀ which reached 45& 60 ppm and 38&59 ppm for A. arvensis and V. tinus, respectively). The effect of sub-lethal concentration, ½ LC_5, of the two plant extracts (26 and 11 ppm, respectively) affected B. alexandrina survival rate to be in the following order, control > V. tinus treated > A. arvensis treated > infected > infected-A. arvensis treated > infected-    V. tinus treated. On the other hand, exposure to those sub-lethal doses caused considerable reduction in the infection percentages. In addition, the histopathological effects of the examined sub-lethal concentrations on hepatopancreatic tubules of the treated snails showed cells vacuolation, presence of hyaline substances filled the lumens of the tubules and necrotic focal areas in case of A. arvnsis and vacuolar degeneration with the necrotic changes in case of V. tinus. While, alterations in the hermaphrodite glands of the treated snails included: degeneration and necrotic changes in the acini. The severity of lesions was progressed with infection as a result of invading of snail tissue by developmental stages of the S. mansoni cercariae. The ultrastructural micrographs were used to explain and confirm the recorded histopathological alterations in the hermaphrodite glands of the infected-treated snails. In comparison with the control and infected snail groups, infected-treated snails showed degeneration with severe deformation and destruction in their reproductive units, degeneration in developmental stages tissues of S. mansoni cercariae and accumulation of the toxic agents.Conclusion: the two examined plants, A. arvensis and V. tinus plant extracts  showed high activity against B. alexandrina  and provide a considerable scope in exploiting local indigenous resources for snail’s molluscicidal agents. The sub-letal concentrations, ½ LC₅, of the two plant extracts caused a considerable reduction in survival rate and infection rate among  S. mansoni infected snails. Histopathological changes in the digestive glands showed cells vacuolation, hyaline substance filled lumens of the tubules and necrotic focal areas in the digestive glands.   Histopathological effects explained and confirmed by TEM images showed degeneration with severe deformation and destruction in the reproductive units.