Toxicity of washing soaps to Schistosoma mansoni cercariae and effects of sublethal concentrations on infectivity in mice.

5 brands of washing powders and a brand of local soap made in Nigeria were tested for toxicity to cercariae of the Nigerian strain of S. mansoni. The tests revealed that all washing soaps were super-toxic to cercariae at high concentrations, with soap bars being comparatively less toxic. The detergents killed all cercariae instantly at 250-4000 ppm while soap bars achieved the same effect between 3000-4000 ppm. At lower concentration 25-100 ppm, the detergents required less than 60 min to kill 100% of the cercariae while soap bars required less than 12 h. The 12 hours LC 50 and LC 90 for Omo (detergent) and local soap were determined. Also the effects of sub-lethal concentrations 1.25-10 ppm on the infectivity of cercariae in mice were evaluated. These tests revealed that the treatment suppressed infectivity and that the degree of suppression increased with increase in the sub-lethal concentration, 85.4% at 10 ppm as compared to 42.8% at 1.25 ppm.