Histopathological changes induced by chemical molluscicides and plant extracts on three economically and medically important gastropod snails

Adult Pomacea canaliculata Lamarck, Cerithidea cingulata Gmellin and Oncomelania hupensis quadrasi Mollendorf were exposed to varying concentrations of chemical molluscicides (metaldehyde and niclosamide) and methanolic neem (Azadirachta indica) seed kernel extract (NSKE) and aqueous leaf extract of Nerium oleander (adelfa) for certain duration, e.g. 24, 48, 72, 96, and 120h, to determine their histopathological effects on the foot and digestive gland of the three snail species. Results showed that the foot of P. canaliculata was more sensitive to metaldehyde than to niclosamide but the opposite was true in the case of the digestive gland. In C. cingulata, the damage caused by metaldehyde was quite greater in the digestive gland than in the foot. The NSKE which was tested only in Pomacea seemed more potent than the aqueous leaf extract from N. oleander given to O.h. quadrasi. The histomorphological alterations observed in the foot were: hyperplasia, swelling and loss of cilia in epithelial cellsbreaks in some areas of the epitheliumincrease in the number of calcium cells and amoebocytes in the subepithelial layer, and absence of secretions from epithelial and subepithelial glands. In the digestive gland, the changes that occurred were: increase in the size and number of calcium pigments, vacuolization of the digestive cells, thinning of the epithelium, widening of the intertubular spaces disintegration of the digestive tubules. No damage, however, were seen in the ontrol snails. The effects were time and dose dependent, and also of a general and not a specific stress response. Detailed biochemical and physiological studies are needed to understand the mechanism of action of the chemical and plant molluscicides on these three gastropod snails. Electron microscopy have to be done to describe better the molluscicides effects on the cellular components of the foot and digestive gland.