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

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

Evaluation of Cercaricidal and Miracicidal Activity of Selected Plant Extracts Against Larval Stages of Schistosoma Mansoni

Schistosomiasis is a parasitic disease caused by blood-flukes of the genus Schistosoma. It is one of the most widespread of all human parasitic diseases, ranking second only to malaria in terms of its socioeconomic and public health importance in tropical and subtropical areas.More than 207 million people, 85% of whom live in Africa, are infected with schistosomiasis,and an estimated700 million people are at risk of infection in 76 countries.Control of schistosomiasis faces serious drawbacks of emergence of drug resistant parasites and molluscicide resistant snail hosts.Due to improper waste disposal,infected faecal matter enter water bodies such as canals rivers and springs where miracidia that hatch from parasite eggs  develop into cercariae inside snail intermediate hosts and are infective to humans upon release in to the water.This study sought to evaluate the miracicidal and cercaricidal activity of selected plant extracts on larval stages of Schistosoma mansoni.Ten cercariae and miracidia were exposed to extract concentrations ranging from 10-150ppm.The most active extracts were Phytolacca dodecandra (LT50 10.84 and16.91minutes) and Solanum linaeanum (LT50 of 22.86 and 26.96 minutes) respectively that killed 50% of miracidia and cercariae in less than 30minutes.This was followed closely by Solanum americanum (LT50 31.02 and 31.89) and Anonna squamosa LT50 35.29 and 40.46minutes respectively.Piper nigrum was the least active recording LT50 46.84 and 56.75 of miracidia and cercaria respectively.Miracidia were more susceptible to extracts than cercariae.The higher susceptibility of miracidia to extracts has also been reported in other studies and it is advantageous since killing one miracidium prevents the formation of thousands of cercariae which are infective to humans.All the extracts killed larvae within one hour at concentration less than 100ppm and could be categorized as potent cercaricide and miracicides. Keywords: Miracidal, Cercaricidal,Schistosomiasis,Phytolacca dodecandra,Solanum linaeanum,Solanum americanum,Anonna squamosa and Piper nigru