Use of ivermectin for transmission blocking of Plasmodium vivax in Anopheles aquasalis and Anopheles darlingi

Background. The use of insecticide-treated nets and indoor residual insecticides targeting adult mosquito vectors is a key element in malaria control programs. However, mosquito resistance to the insecticides threatens malaria control efforts. Alternative methods like ivermectin (IVM) administration to humans has been suggested as a possible vector control tool to reduce Plasmodium transmission. Anopheles aquasalis and Anopheles darlingi are competent vectors for Plasmodium vivax in the coast of Brazil and the Amazon region, respectively. Material and Methods. (A) One single IVM dose (200 µg/mL) was ingested by volunteers and blood samples were drawn at distinct times (0, 4 hours, 1, 5, 10, 14 days). Anopheles aquasalis and An. darlingi were infected by membrane feeding P. vivax from malaria patients. Patient plasma was removed and replaced with plasma from IVM-treated volunteers. Seven days after the infection, the mosquitoes were dissected to check the oocyst presence and for An. darlingi also the sporozoite presence at day 14. (B) The ex vivo effect of the addition of ivermectin on cultivated P. vivax was observed. (C) The effect of IVM on malaria vivax patients infectivity to Anopheles was analyzed: different regimes treatment Chloroquine (CQ)+IVM, CQ+Primaquine (PQ) and CQ+IVM+PQ. Results. IVM significantly reduced the prevalence of An. aquasalis that developed oocysts (40, 20 and 10ng/mL compound; 4 hours, 1 and 5-day plasma). In An. darlingi oocyst prevalence and intensitywas only reduced with plasma from 4 hours and 1 day. Mosquito mortality was increased in Anopheles aquasalis that ingested 40 ng/mL ivermectin compound and plasma from 4 hours, 1, 5, 10 and 14 days post-intake, and in An. darlingi that ingested plasma from 4 hours and 1 day post-intake, recording 100% mortality 14 days post-feeding with 4 hour,1 and 5-day plasma. The double fled of IVM by the mosquitos has a significant impact on the proportion of infected mosquitos. The oocyst prevalence and intensity was significantly reduced in comparison to control on mosquitos fed with unprocessed blood from patients that undertook CQ+IVM, CQ+PQ and CQ+IVM+PQ. In the ex vivo cultures, ivermectin (plasma 4 hours) significantly inhibited P. vivax asexual development, reducing the number of schizonts. Conclusion. Ivermectin reduces the oocyst prevalence and intensity of P. vivax in An. aquasalis and An. darlingi, and increased the mortality of mosquitos. These findings support that ivermectin is useful to reduce P. vivax transmission.