Evaluation of the Effects of Papain on Schistosoma mansoni: Miracidial Infection Capacity, Infection Prevalence, Cercarial Shedding and Molecular Changes in Biomphalaria alexandrina.

Purpose: The aim of the present study is to assess the molluscicidal, larvicidal and genotoxicological activities of papain and how it can affect the host-parasite interactions.

Methods: Toxicity of papain on snails by making series of concentrations to calculate LC₅₀, and then study its larvicide effect on the free larval stages of S. mansoni and infection rate of snails.

Results: Papain has a molluscicidal activity on adult snails of Biomphalaria alexandrina with a lethal concentration LC₅₀ equals to 43.1 mg/L. In addition, it has activity on miracidia with half Lethal time (LT₅₀) of 16.11 min., and on cercariae with 12.1 min. compared to control ones. The sub lethal concentration LC₁₀ and LC₂₅ (6.9 or 24.1 mg/L, respectively) decreased the survival rate of snails at the first cercarial shedding, the rate of infection, the average total number of cercariae per snail, the shedding period and the life span of snails, while the prepatent period was significantly increased than the control ones. The morphological alterations in cercariae after exposure to papain were occurred where the cercariae lacked motility and some had a dark tail with complete detachment of head and tail. Compared to the control group, the levels of cytochrome oxidase subunit I (COI) and (ND1) genes significantly decreased in snails after exposure to papain.

Conclusions: Papain could be used as a potential molluscicide for elimination of schistosomiasis and decrease its transmission and deterioration of host-parasite interaction.