Mosquito-Disseminated Insecticide for Citywide Vector Control and Its Potential to Block Arbovirus Epidemics: Entomological Observations and Modeling Results from Amazonian Brazil

Background Mosquito-borne viruses threaten public health worldwide. When the ratio of competent vectors to susceptible humans is low enough, the virus’s basic reproductive number (R0) falls below 1.0 (each case generating, on average
Fernando Abad-Franch and colleagues report entomological observations before and after citywide mosquito control in Amazonian Brazil, and model the estimated impact on transmission of mosquito-borne viruses.
Author Summary Why Was This Study Done? Urban mosquitoes are global public health threats. They transmit dengue, Zika, and many other diseases for which vaccines or drugs are not available. Mosquito control is the key to preventing these diseases, yet conventional control tactics seldom yield satisfactory results. One key drawback is that many mosquitoes (especially Aedes) use small, hidden, or inaccessible breeding sites (aquatic larval habitats) that often remain untreated during control campaigns. One way of increasing the fraction of breeding sites that are treated is to use the mosquitoes themselves to transfer pyriproxyfen (PPF), a potent juvenile-killing insecticide, from resting sites to untreated breeding sites; there, PPF impedes juvenile mosquito development. What Did the Researchers Do and Find? Working with municipal vector control staff, we tested mosquito-disseminated PPF in a 60,000-inhabitant town of central Amazonia, in Brazil. We sampled juvenile mosquitoes monthly in 100 dwellings over 12 baseline months, eight months of PPF dissemination (five months citywide and three months focal), and three months post-dissemination. We caught 12,817 Aedes albopictus and 5,346 Ae. aegypti juveniles, and kept them in the laboratory to measure juvenile mortality and adult emergence. Following PPF dissemination, we observed an 80%–90% decrease in Aedes juvenile catch, while Aedes juvenile mortality increased from 2%–7% to 80%–90%. Adult Aedes emergence dropped by 96%–98%, such that the number of females emerging per person decreased to 0.002–0.129 females per person-month. Mathematical models predict that this reduction would effectively block transmission of mosquito-borne viruses like dengue, Zika, or chikungunya. What Do These Findings Mean? Our findings suggest that mosquito-disseminated PPF has the potential to become an important public health tool; larger, carefully designed trials are now necessary to determine the impact of this tactic on disease transmission.