Molluscicidal Activity of Selected Plant Extracts in Kenya

Abstract

Schistosomiasis is a snail-borne infection and one approach to the control of schistosomiasis is elimination of the intermediate host. The use of synthetic molluscicides is becoming unpopular and as a result, plant molluscicides have received considerable attention in search for cheaper alternatives to synthetic molluscicides. In this study, the molluscicidal activity of aqueous and ethanol extracts of selected plants against adult and juveniles of Biomphalaria pfeifferi snails was investigated. Dried plant materials from Ocimum americanum, Sonchus luxurians, Aloe secundiflora, Bridelia micrantha and Croton megalocarpus were ground into powder and extraction done using ethanol and water. Phytochemicals were tested which include; flavonoids, saponins, tannins, alkaloids, glycosides, steroids and triterpenes. Ten adult and ten juvenile Biomphalaria pfeifferi snails were exposed to serial dilutions of 5 mg/l, 10 mg/l, 20 mg/l and 40 mg/l of the aqueous and ethanol plant extracts. The exposure period was 48 h. The LD₅₀ value of the plant extracts was determined. The lethal dose, LD₅₀ of B. micrantha against the adult snails was 24.98 mg/l for the aqueous extract and 19.01 mg/l for the ethanol extract. The lethal dose, LD₅₀ of B. micrantha against the juvenile snails was 22.860 mg/l for the aqueous extract and 26.30 mg/l for the ethanol extract. The other extracts from the other plants were found to have a LD₅₀ value of above 100 mg/l.Generally, only B. micrantha which had molluscicidal activity against adult and juvenile snails. B. micrantha extracts, that were found to have molluscicidal activity, were screened for their miracicidal and cercaricidal activity against Schistosoma mansoni miracidia and cercariae using concentrations of 5 mg/l, 10 mg/l, 20 mg/l and 40 mg/l. The exposure period was 1h. Bridelia micrantha aqueous extract had a LD₅₀ value of 11.108 mg/l on the S. mansoni miracidia and a LD₅₀ value of 4.465 mg/l on S. mansoni cercariae. The ethanol extract was found to have a LD₅₀ value of above 40 mg/l for the miracidia and the cercariae. From this study, B. micrantha demonstrated molluscicidal activity against Biomphalaria pfeifferi snails and miracicidal and cercaricidal activity against Schistosoma mansoni miracidia and cercariae.

Keywords: Molluscicidal, Phytochemicals, Miracicidal, Cercaricidal.