Laboratory evaluation of B-2 as a molluscicide in the control of the snail intermediate hosts of schistosomiasis in South Africa.

There is a continuous need for the development and evaluation of new, inexpensive but highly effective molluscides for the control of freshwater snails acting as intermediate hosts of schistomiasis. For this reason B-2 (Hokko Chemical Industry Co. Ltd, Japan), also called Phebrol (sodium 2,5-dichloro-4-bromophenol), was evaluated in our laboratory as a candidate molluscicide for the control of freshwater snails in South Africa. Bulinus africanus and Biomphalaria pfeifferi, intermediate hosts of Schistosoma haematobium and Schistosoma mansoni respectively, were exposed to different B-2 concentrations for 24 and 48 hours. An indigenous fish species, Oreochromis mossambicus, which is common in local schistosomiasis endemic areas, was also exposed to the molluscicide. The calculated values obtained from a probit analysis (LC50, 24 hours: B. africanus = 2.6 mg 1(-1) and B. pfeifferi = 2.9 mg 1(-1), indicated that these species from southern Africa are less sensitive to B-2 than are B. truncatus and B. pfeifferi from northern Africa, which in turn are less sensitive than the Oncomelania spp. from Japan, China and the Philippines. It is expected that molluscicidal levels of B-2 would be harmful to O. mossambicus populations. Although B-2 has a marked potential for snail control in South Africa, niclosamide (Bayluscide) remains the molluscicide of choice.