The effect of sublethal doses of a molluscicide (Bayluscide) on the development of Schistosoma mansoni in Biomphalaria sudanica tanganyicensis.

The complete eradication of snails from waterbodies is rarely achieved with existing molluscicides. This communication describes laboratory experiments designed to show whether snails surviving such treatment are still capable of transmitting Schistosoma mansoni. The treatment, with Bayluscide, was given at various times during the development of the infection. Snails that survived treatment were as susceptible to infection as were untreated controls but, although the initial survival rate of infected snails was as good as that of uninfected snails, their ultimate survival rate was poorer. Treatment had no permanent effect on the development of the schistosome, although there is some evidence of a delay in some cases. Infected snails may survive a field application of Bayluscide and continue parasite transmission, and uninfected survivors are susceptible to infection. Thus, while it may curtail transmission dramatically, the use of molluscicides will not eliminate transmission in the absence of other measures to prevent infection of the surviving snails.