The relative susceptibilities of Bulinus truncatus (Audouin) and Sarotherodon mossambicus (Peters) to certain molluscicides

• Main Author: Daffalla, A. A.
• Other Authors: Duncan, J. ; Webbe, G.
• Published: London School of Hygiene and Tropical Medicine (University of London) 1978
• Subjects: 590
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.452857

In spite of varying opinions as to the effectiveness of molluscicides in the control of schistosorniasis, the search for more effective and highly selective molluscicides should continue, so that adverse effects on non-target organisms caused by commercially available molluscicides may be reduced and the possibility of resistance guarded against. To this end, the differences in susceptibility to Frescon and 4'-chloronicotinanilide between the schistosome-bearing snail, Bulinus truncatus and a representative tropical food fish, Sarotherodon mossambicus, were examined and discussed in relation to the rate of uptake of these compounds and. their distribution among different organs. The rate at which water is taken up by B. truncatus and S. mossambicus has also been calculated and related to the rate of uptake of molluscicidos. This part of the work was an attempt to elucidate the mechanism of carriage of the chemicals into the animals being studied. It has been demonstrated that B. truncatus and S. mossambicus concentrate Frescon and 4'-chloronicotinanilide to high levels. For B. truncatus, both Frescon and 4'-chloronicotinanilide were concentrated in the psoudobranch, while in S. mossambicus the highest concentration of Frescon was found in the liver and that of 4'-chloronicotinanilide in the bile. The high tolerance of S. mossambicus to 4' -chloronicotin anilide was found to be due to the rapid metabolism of the compound in fish to more polar forms which are more easily disposed of-via the bile. Comparison of the relative susceptibilities of two field collections of B. truncatus showed that snails collected from the Frescon--treated area of the Gezira display a higher tolerance to Frescon than do snails collected from the untreated area. Frescon uptake rate was found to be lower in the less susceptible snails, and this is tentatively suggested as the basis of the observed difference in tolerance. It is additionally shown that B. truncatus infected with Schistosoma haematobium is more susceptible to Frescon than uninfected snails.