Malaria incidence was projected to decline to 263 million cases and 597,000 fatalities by 2023. Vector management, specifically the usage of Long-Lasting Insecticides (LLINs), had an important role in the reduction of malaria cases. However, the rising prevalence of pesticide resistance threatens the continued effectiveness of these interventions. Targeting parasites within mosquitoes offers a promising strategy to interrupt parasite transmission and reduce malaria incidence. The antimalarial drug atovaquone is used to kill Plasmodium falciparum within the anopheline mosquito, thereby inhibiting parasite development. Integrating a Plasmodium-specific chemical in existing LLINs may decrease the malaria cases in Sub-Saharan Africa, especially in areas with high pesticide resistance.
Female Anopheles gambiae G3 mosquitoes (aged 4–7 days) were fed on 14–21-day-old Plasmodium falciparum NF54 cultures containing stage V gametocytes using 37 °C membrane feeders. After 60 minutes of feeding, fully engorged mosquitoes were moved to a biosafety glovebox, while partially fed ones were discarded. Mosquitoes were maintained at 27 °C, 70–80% humidity, with access to water and 10% sugar under a 12-hour light–dark cycle. Topical applications of compounds were prepared by using 2% dimethyl sulfoxide (DMSO) stocks and stored at -20 °C. Tarsal-contact assays were performed by using tarsal-contact plates prepared by calculating the amount of compound necessary to coat a 6-cm-diameter glass Petri dish at 1 mmol m2. The adjuvant Mero was added to each solution, which has previously been shown to act as an uptake excipient in mosquito tarsal-contact assays.
Oocyst dissection and quantification were performed by dissecting midguts into 1× PBS, staining them with 0.2% w/v mercury dibromofluorescein disodium salt solution, and counting sporozoites with an Olympus Inverted CKX41 microscope. Live ookinete immunofluorescence assays (IFAs) were applied to mosquitoes before an infectious blood meal, and approximately 200 parasites per group were live counted and classified as zygote, intermediate retort form, or ookinete based on parasite morphology.
The study aimed to determine the effect of asexual blood-stage parasite culture on resistance to asexual blood-stage parasites. Two compounds (DSM703 and DSM161) exhibited 100% prevalence, and the study used CACTI to evaluate compound libraries and analogues for a compound library.
A study aimed to identify small-molecule compounds that inhibit mosquito-stage P. falciparum development. Researchers conducted an in vivo topical-application screen on female Anopheles gambiae mosquitoes, identifying 22 compounds that significantly reduced parasite infection. Immunofluorescence assays showed that Na+ ion homeostasis and protein synthesis play a crucial role in parasite differentiation. The study also explored the effectiveness of structural modifications to compounds to influence their tarsal-based efficacy of antimalarials. Endochin-like quinolones (ELQs) were the primary hit, showing efficacy in tarsal-contact assays. The researchers designed ELQ Qi-site prodrugs with modifications to their 3-position side chains and tested them for improvements in tarsal-based uptake efficacy.
The degree of uptake through mosquito tarsi is strongly affected by the compound’s structure, which is key to its activity against P. falciparum. Combination therapy is now considered the mainstay for malaria therapeutics, as it improves efficacy and reduces the probability of rapid emergence of parasite resistance compared to monotherapy. The study demonstrated that a single, short period of mosquito contact with surfaces treated with the ELQ combination can prevent infection establishment and slow down ongoing infections, extending the parasite developmental time in the mosquito.
Reference: Probst AS, Paton DG, Appetecchia F, et al. In vivo screen of Plasmodium targets for mosquito-based malaria control. Nature. doi:10.1038/s41586-025-09039-2
