Hemocyte, Biochemical, and Histopathological Responses of Biomphalaria alexandrina , the Egyptian Intermediate Host of Schistosoma mansoni , to Sublethal Deltamethrin Exposure

ABSTRACT Deltamethrin is among the pyrethroids most frequently detected in Egyptian irrigation canals and drains, the same water bodies that support Biomphalaria alexandrina , the snail that transmits Schistosoma mansoni in Egypt. The objective of this study was to characterize the response of adult B. alexandrina to sublethal concentrations of a commercial deltamethrin formulation, using hemocyte, biochemical, and histopathological biomarkers. The hypothesis tested was that sublethal deltamethrin reduces the number of circulating hemocytes, alters the balance between hemocyte classes and damages hemocyte structure, at concentrations comparable with those measured in Egyptian watercourses. Adult snails were exposed to a commercial deltamethrin emulsifiable concentrate, the form applied in the field. The 24‐h median lethal concentration (LC 50 ) was 0.41 mg/L as nominal active ingredient. Snails were then held for 48 h or 10 d at nominal LC o (0.04 mg/L), LC 5 (0.25 mg/L), and LC 10 (0.28 mg/L), the lowest of these being 1.2‐fold the highest deltamethrin concentration so far reported from Giza‐area watercourses. Circulating hemocytes fell by 35% after 48 h and by 45% after 10 d at LC 10 ( p < 0.001). The differential profile shifted toward granulocytes, from 66% in the 10‐d control to 84% at LC 10 ( p < 0.001), at the expense of hyalinocytes and blast‐like cells. Exposed cells showed retracted pseudopodia, incomplete mitotic figures, cytoplasmic vacuolization, and membrane rupture. Binucleate hemocytes rose from 12.50% to 35.87% and micronucleated cells from 2.63% to 6.43% ( p < 0.001). Aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glucose rose while total protein and albumin fell; reduced glutathione (GSH) rose alongside malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ); and the digestive gland and the ovotestis degenerated with concentration. The hypothesis was accepted. The hemocyte compartment is a sensitive target of sublethal pyrethroid exposure in a snail of direct public health importance.