The effects of bayluscide and malathion on the mortality and infectivity of Schistosoma mansoni cercariae

Abstract

AbstractLaboratory experiments were conducted to assess the effects of bayluscide and malathion on the mortality and infectivity of Schistosoma mansoni cercariae. Mortality of cercariae varied with time of exposure and concentration of tested chemicals. The LC5, LC50, and LC95 for bayluscide were 0.04, 0.07, and 0.10 ppm after 2 h of exposure; 0.03, 0.04, and 0.06 ppm after 4 h of exposure; and 0.02, 0.03, and 0.05 ppm after 6 h of exposure, respectively. Malathion gave LC5, LC50, and LC95 values of 59.16, 107.07, and 193.78 ppm after 2 h of exposure; and 39.79, 69.36, and 120.89 ppm after 4 h of exposure, respectively. Sublethal concentrations of bayluscide and malathion significantly reduced the rate of infection of laboratory mice by S. mansoni cercariae (p < 0.01). Approximately 1.50 and 0.00% of adult worms were recovered by autopsy of mice whose cercariae were preexposed for only 1 h to 0.04 ppm of bayluscide and 50.00 ppm of malathion, respectively. These results clearly show that bayluscide is much more toxic to cercariae than to snail intermediate hosts cited in the literature, and that malathion possesses some cercaricidal properties at concentrations expected to be achieved in the field.