Contact-mediated triclosan delivery for transmission blocking of Plasmodium in Anopheles stephensi

Extensive and long-term insecticide use has led to the development of resistance in mosquito vectors, underscoring the need for novel insecticidal molecules and integrated, multifaceted strategies that simultaneously target both the vector and the parasite. In line with this, we evaluated the potential of a lipophilic drug triclosan, as a contact-mediated inhibitor to block the development of Plasmodium parasite within the malaria vector, Anopheles stephensi.

Molecular docking and simulations identified the potential of triclosan to interact with the ookinete surface proteins of the Plasmodium species. Intrinsic toxicity of triclosan was first established on both larval and adult stages of laboratory reared An. stephensi through oral feeding and contact exposure (topical application and bottle bio-assay) in terms of survival and/or fecundity and egg hatchability. The transmission blocking potential of triclosan was initially tested in vitro using exflagellation assays and ookinete development assays. Finally, studies with P. berghei challenged mosquitoes were done to check the in vivo transmission blocking activity of triclosan through bottle bioassays.

Docking and simulations showed stable binding of triclosan to Plasmodium ookinete surface proteins. Contact exposure of triclosan was non-toxic for adult mosquitoes. However, parasite development was markedly affected. We observed a concentration dependent reduction in exflagellation centers and ookinete formation with increasing concentrations of triclosan compared to the control group. However, at 70 μM concentration, a significant reduction of 87% in exflagellation centers was observed. There was a substantial reduction in ookinete formation; at 50 μM, it was 97.7%, while at 70 μM, the reduction reached 99%. In vivo, triclosan exposure resulted in a substantial decrease in oocyst development, with reductions of up to 86% at higher concentrations.

These findings demonstrate triclosan as a contact-mediated anti-Plasmodium agent that disrupts parasite development within the mosquito vector, underscoring its potential as a novel vector-targeted transmission blocking intervention against malaria.