Evaluation of the Molluscicidal Effects of Aqueous and Ethanol Extracts of Carica papaya as Potential Molluscicides against B. pfeifferi, Adult Snails, a Vector of Schistosomiasis

Abstract

The study was carried out to evaluation of the molluscicidal effects of aqueous and ethanol extracts of Carica papaya as potential molluscicides against B. pfeifferi, adult snails, a vector of schistosomiasis. The plant was sourced from Sokun village where it is traditionally used to treat infections. The stem bark were peeled and air dried at room temperature then crushed and sieved to standardized particles, and extracted in ethanol and distilled water. Phenols were the most abundant phytochemicals in all extracts except the seeds ethanol extracts where they were not detected. Cardiac glycosides were found in all the extracts but in trace amounts. Seeds extracts had high amounts of alkaloids while the stem lacked alkaloids. The extract of stem ethanol was the most effective, killing all the 10 snails (100%) exposed to it at the lowest and highest concentrations (50mg/l and 150mg/l). Other extracts that caused 100% mortality are the seeds ethanol extract (150 mg/l) and stem water extract (150mg/l). The maximum number of snails killed by the stem water extract was 104.65%. LD₅₀ is the minimum dosage required to kill 50% of the snails. The extract of the stem ethanol had the lowest calculated LD₅₀ of 2.437mg/l followed by the stem water extract (104.65mg/l). The water extract of the seed ethanol recorded the highest LD₅₀ of 127.71mg/l. The maximum number of miracidia killed by the stem ethanol extract was 3 at a concentration of 10mg/l. 15mg/l and 5mg/l of the stem ethanol extract killed 1 miracidium each. The lowest LT₅₀ was 70.77 minutes recorded for 10mg/l of the stem ethanol extract. LT values for 5mg/l and 10mg/l of seeds water extracts could not be computed because they did not kill miracidia. The results indicated that miracidia exhibited a high level of tolerance to all extracts from this plant. At low concentrations of 50,100 and 150µg/l no deaths were recorded for all plant extracts. When the concentrations were increased to 50, 100, and 150mg/l cercariae exhibited intolerance which was dose and time dependent. The ethanol extract of the seeds was the most lethal to cercariae. At a dosage of 100mg/l and 150mg/l all the 10 (100%) cercariae exposed to this extract were dead at 15 minutes and 45 minutes respectively. The highest concentration of seeds water extract killed a maximum of 5 cercariae. The results were subjected to Finney Probit analysis using Biostat 2009, to determine (LT₅₀) for the plant 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.