Evaluating phytochemical profiles, molluscicidal and schistosomicidal activity of aqueous and ethanol extracts of vernonia amygdalina and harrisonia abyssinica

Schistosomiasis is considered one of the neglected tropical diseases caused by blood flukes. The disease kills 200,000 people annually in Sub Saharan Africa and stunts cognitive and physical growth. In Kenya, the total population requiring preventive chemotherapy in the year 2015 was estimated at 2.5 million out of which 1.8 million were school aged children. Fresh water snails of genus Biomphalaria are the intermediate hosts of S. mansoni. Chemical molluscicides used to control snails also kill non target species and have long term detrimental effects to the environment. Chemotherapy is thus the most widely applied control method. Praziquantel is the only drug recommended for mass administration hence there is a high risk of developing resistance. The search for alternative molluscicidal and schistosomicidal herbs is inevitable. This study investigated the molluscicidal and schistosomicidal potential of Vernonia amygdalina and Harrisonia abyssinica known for their broad spectrum medicinal values. The plants were sourced from Bungoma County where they are traditionally used to treat worm infections. The root and stem bark were ripped off using a knife and air dried at room temperature then crushed and sieved to standardized particles, and extracted in ethanol and distilled water. The extracts were qualitatively screened for phytochemicals by reacting the plant extracts with standard reagents and observing color change. V. amygdalina was rich in saponins, glycosides and phenols while H. abyssinica had abundant phenols, and alkaloids. Batches of ten snails were exposed to each of the plant extracts at 50, 150 and 300 mg/l in 500 ml plastic containers. One positive and one negative control were set using niclosamide and distilled water respectively. The numbers of dead snails were counted and recorded after 24 hours. Ten miracidia and ten cercariae were exposed separately in each well of a 24 well microtitre plate to lower concentrations of 5, 15 and 30 μg/l and monitored for 60 minutes. This was followed by exposure to higher concentrations of plant extracts at 50, 150 and 300 mg/l and monitoring for another 60 minutes. The number of dead miracidia and cercaria were enumerated and recorded at 5, 10, 15, 20, 30, 45 and 60 minutes. Data on snail deaths were analyzed using ANOVA at p ≤ 0.05 to compare the three dosages of plant extracts followed by the Dunnet test to compare with the positive control. Harrisonia abyssinica root water extracts had the highest molluscicidal activity, similar to the positive control, Niclosamide (50 mg/l p = 1.00, 150 mg/l p = 0.095, 300 mg/l p = 1.00). Finney probit analysis was used to calculate the LD50 for snails and LT50 for miracidia and cercariae. The root water extract of H. abyssinica was the most effective against snails with the lowest LD50 value of 2.437 mg/l while the stem ethanol extract of V. amygdalina was the most effective cercaricidal agent (LT50 of 6.72 minutes). The best miracicidal agent was 300 mg/l of V. amygdalina stem water extract (LT50 57.73 minutes). H. abyssinica root extracts should be considered for development of molluscicides since they had the best LD50 value. The stem ethanol extracts of V. amygdalina can be considered for development of cercaricidal agents in combination with other plants proved to have cercaricidal properties since the extract was lethal at high dosages. Miracidia were relatively tolerant to extracts from the two plants hence the plants may not be good candidates for miracicidal activity as stand-alone extracts. This study provides baseline information which can be used by pharmaceutical companies, researchers and the ministry of health in their quest to develop new molluscicides and schistosomicides.