The effects of lead, cadmium, and mercury on the mortality and infectivity of Schistosoma mansoni cercariae

The effects of lead, cadmium, and mercury chloride salts on survival and infectivity of Schistosoma mansoni cercariae were examined. The LC 50 for 5 hr exposure was approximately 500 mu M for lead, 2.5 mu M for cadmium, and 6 mu M for mercury. These toxicity figures are significantly higher than the levels of these heavy meals reported to occur in the natural waters of Egypt where schistosome transmission occurs. Infectivity of cercariae surviving exposure to metals at the LC 50 was reduced to approximately one-half that of control mice infected with unexposed cercariae.