Regulatory Influence of Procambarusclarkii, Girad (Decapoda: Cambaridae) On Schistosome-Transmitting Snails in Lotic Habitats within the River Athi Basin, Kenya

Abstract

Background & Objective: Control of schistosomiasis, a neglected tropical disease has for a long time overly relied on praziquantel. Crayfish, though voracious snail eaters have been tested in small man-made impoundments but not in lotic habitats. The present study aimed to determine the ability of the crayfish, Procambarusclarkii to reduce populations of schistosome transmitting snails in lotic habitats.

Methods: Data was collected bi-monthly on the presence or absence of snails and crayfish in4 stream habitats, over a period of 10 months, and these were identified from a baseline survey to be habitats for Biomphalaria snails, transmitters of intestinal schistosomiasis, and were located in the Machakos County within the Athi River basin in south-eastern Kenya. Subsequently, 2 of the habitats were selected for introduction of crayfish (and were designated “experimental sites”) and the other 2 habitats were designated “control sites.” Each of the “experimental sites” received 110 crayfish. The study sites were sampled for snails using standard snail scoops and for crayfish using meat-baited crayfish traps. The bi-monthly sampling of the habitats was done to determine snail abundance, crayfish survival, and obtain information on biotic and abiotic parameters.

Results: Snail abundance in the habitats that received crayfish rapidly declined within 2 months to a significant level compared with the initial abundance (paired t test = 5.524, p value = 0.0001), relative to the decline observed in the control habitats (paired t test = 7.727, p value = 0.082).

Interpretation & Conclusion: While P.clarkiiholds much promise as a complimentary schistosomiasis control strategy to chemotherapy, restocking of habitats should be considered when habitats dry up during extreme weather conditions, for effectiveness of this approach.