Molluscicidal Activity of Selected Plant Extracts against Adult and Juvenile Biomphalaria Pfeifferi

Abstract

Human Schistosomiasis is a debilitating infection whose transmission depends solely on the presence of snail intermediate hosts. It is a major public health problem second only to malaria in terms of morbidity and mortality and predominant in tropical and subtropical countries. Globally, over 240 million people are infected and close to 600milion are at risk.Strategies for Control of Schistosomiasis include; Chemotherapy with praziquantel, mollusciciding with Niclosamide, health education, community participation, provision of clean water and improved sanitation. Chemotherapy and use of synthetic molluscicides faces serious drawbacks of being costly, poses negative impact on environment and development of resistant strains of intermediate host snails and parasites. Plant extracts that are effective against host snails and non-toxic to non-target organisms could provide an alternative molluscicide to the current Niclosamide.This study evaluated molluscicidal activity of aqueous and methanol extracts against juvenile and adult Biomphalaria pfeifferi in vitro.Assesment of snail susceptibility to extracts was done by immersion method in accordance to WHO protocal.10 adult and juvenile snails were exposed separately to serial dilutions of 10, 20, 50, 100 and 150ppm (mg/l) of both aqueous and methanol extracts for 48 hours. Mean mortality of snails was subjected to probit analysis to determine the lethal dose (LD₅₀) that killed 50% of the snails. The most active extracts on both juvenile and adults were Phytolacca dodecandra (LD₅₀ 8.78 and 12.58ppm) and Solannum linaeanum (LD₅₀ 16.81 and 23.25ppm) respectively.This was followed by Solanum americanum (LD₅₀ 36.17 and 38.00ppm) and Annona squamosa (LD₅₀ 51.96 and 59.00ppm) respectively. The least active extracts were Piper nigrum (LD₅₀ 74.13 and 89.95ppm) and Rhizophora mucranata LD₅₀ 94.56 and 109.82 ppm) respectively. Average mortality of Phytolacca dodecandra and solanum linaeanum was significantly similar (p ˃ 0.05) to that of niclosamide the currently used molluscicde.Since a good molluscicide should kill snails at a concentration of 100ppm or lower, this study demonstrated potency of four plant species from Kenya with molluscicidal activity against the intermediate hosts of Schistosoma mansoni.

Keywords: Schistosomiasis, Biomphalaria pfeifferi, Schistosoma mansoni, Molluscicide, Phytolacca dodecandra, Solanum linaeanum, Solanum americanum, Annona squamosa.