Abstract

Objective: To elucidate the effect of the parasitic nematode Phasmarhabditis hermaphrodita (P. hermaphrodita) as snail biocontrol agent on biological, parasitological, biochemical and molecular parameters of Biomphalaria alexandrina (B. alexandrina) snails, the intermediate host of Schistosoma mansoni (S. mansoni). Methods: B. alexandrina snails (5–6 mm) were exposed to the 3rd stage larvae of the nematode P. hermaphrodita and/or S. mansoni miracidia for 24 h. Thereafter, they were thoroughly washed with clean dechlorinated water and transferred to clean aquaria for recovery and recording deteriorations in their biological, parasitological, biochemical and molecular parameters. Results: The results showed that snails were dead after 24 h of exposure to 100 nematode larvae/snail. Cercarial production/infected snail was reduced to 68 cercariae/snail post simultaneous exposure to 40 nematode larvae and 10 S. mansoni miracidia compared to control (783.7 cercariae/snail) (P < 0.001). Similarly, the total hemocytes of snails increased to 3 800 hemocytes/mL hemolymph by the 3rd day post exposure compared to 2 100 hemocytes/mL for control group (P < 0.001). The results, also, elicited a significant elevation in activities of the enzymes aspartate transaminase, alanine transaminase, acid phosphatase and alkaline phosphatase in hemolymph of snails exposed to nematode larvae. Similar pattern was recoded for activities of catalase, glutathione reduced and nitric oxide in snails’ digestive gland. Meanwhile total protein and albumin concentrations in snails’ hemolymph and lipid peroxide in digestive gland tissues were decreased. The electrophoretic analysis of ovotestis-digestive gland complex of snails exposed to the nematode larvae indicated an increase in RNA intensity, while no significant changes were recorded in the molecular weight of intact DNA compared to control snails. Conclusions: It is concluded that exposure of B. alexandrina snails to P. hermaphrodita nematode deteriorates their biological, parasitological, biochemical and molecular parameters, rendering them to be unsuitable for schistosomiasis transmission. However, comprehensive tests are needed to determine efficacy of P. hermaphrodita as a schistosomiasis biocontrol agent aiming to incorporate in control program of this parasite.

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