Larvicidal and macrofilaricidal efficacy of Closantel and Morantel against mosquito larvae and Setaria digitata nematodes

IntroductionVector-borne diseases (VBDs) are responsible for 17% of all infectious disease cases globally and contribute to over 700,000 deaths each year (WHO, 2020). Currently, more than 80% of the world’s population reside in areas endemic for vector-borne diseases (Franklinos et al., 2019). In recent years, many mosquito-borne diseases have risen in prevalence and geographic distribution due to climate change and land-use changes. According to current climate trends, scientists predict that the population at risk for dengue and malaria will increase by 4.7 billion people by 2070 (Colón-González et al., 2021). India experiences endemic mosquito-borne diseases, including dengue, malaria, chikungunya, Japanese encephalitis, and lymphatic filariasis (Naik et al., 2023). Of all mosquito-borne diseases, dengue virus currently contributes the largest burden of cases and deaths. Aedes aegypti mosquitoes are a primary vector for dengue in India, and they also participate in the transmission of Chikungunya and Zika viruses (Hussain et al., 2022). While malaria incidence in India has decreased by nearly 50% in recent years, India holds 66% of the WHO SEA region’s malaria burden (World Malaria Report, 2023, Singh et al., 2024). In urban regions of India, malaria is primarily transmitted by Anopheles stephensi (Thomas et al., 2017). Additionally, lymphatic filariasis (LF) is a neglected tropical disease transmitted primarily by Culex quinquefasciatus mosquito in India (Agrawal, 2006). 40% of the global burden of LF occurs in India (Pati, 2023). An innovative approach for addressing VBDs is repurposing drugs that are already clinically researched and widely distributed. The benefits of repurposed drugs include reduced cost and increased expediency of drug development because existing safety data and manufacturing processes can be used, reducing the time and resources required by the drug development process (Hamid et al., 2024). Thus, repurposed drugs can potentially aid unmet medical needs with limited funding, such as Neglected tropical diseases (NTDs) and vector-borne diseases (VBDs). In this study, two repurposed drugs, closantel, and morantel were evaluated for their mosquito larvicidal and macrofilaricidal activities to meet the needs of NTDs and VBDs.Materials and methodsMosquito larvaeEarly 4th stage larvae of Aedes aegypti L., Anopheles stephensi Liston., and Culex quinquefasciatus Say., were used for the present study obtained from our insectary, that was maintained at a temperature of 28°C, 80% humidity, and 12:12 photoperiodism.S. digitata collectionFor this reason, Setaria digitata worms, a cause of filariasis in cattle, were selected as model organisms due to their similarities in morphology and histology to W. bancrofti (Decruse, 1990). Adult female Setaria digitata worms were collected from the intraperitoneal cavity of freshly slaughtered cows at a slaughterhouse in the Sulthanpet locality, Puducherry, India (11.919369771639419° N, 79.75910073436751° E) in 0.85% normal saline. Worms were transferred into fresh normal saline upon reaching the laboratory. They were washed in phosphate-buffered saline (PBS) solution and then introduced individually in Petri plates containing 1.36% Dulbecco’s Modified Eagle (DME) medium supplemented with 10% heat-inactivated fetal bovine serum (FBS). Worms were immediately transported and used in laboratory experiments within two hours.Drug procurement and preparationIn the present study, two repurposed drugs, namely closantel and morantel, were selected according to the demonstrated anthelmintic activity in literature. Closantel and morantel are veterinary antiparasitics that were low cost and procured from local veterinary medical supply stores in Puducherry, India. For drug solution preparation, 10 mg of active ingredient was prepared in 10 mL of solution, resulting in a solution with 1000 ppm (1mg/1ml) active ingredient. Initial solubility showed the highest solubility of both closantel and morantel in dimethyl sulfoxide (DMSO). Last, sonication was used to achieve maximum solubility of the drug. Then the mosquito larvicidal and macrofilaricidal experiments were conducted.ConclusionThis study identifies morantel and closantel as promising drugs to research in the development of macrofilaricides for Lymphatic Filariasis and against mosquito larvae.