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

Abstract

BackgroundMosquito-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, <1.0 additional case) and the infection fades out from the population. Conventional mosquito control tactics, however, seldom yield R0 < 1.0. A promising alternative uses mosquitoes to disseminate a potent growth-regulator larvicide, pyriproxyfen (PPF), to aquatic larval habitats; this kills most mosquito juveniles and substantially reduces adult mosquito emergence. We tested mosquito-disseminated PPF in Manacapuru, a 60,000-inhabitant city (~650 ha) in Amazonian Brazil.Methods and FindingsWe sampled juvenile mosquitoes monthly in 100 dwellings over four periods in February 2014–January 2016: 12 baseline months, 5 mo of citywide PPF dissemination, 3 mo of focal PPF dissemination around Aedes-infested dwellings, and 3 mo after dissemination ended. We caught 19,434 juvenile mosquitoes (66% Aedes albopictus, 28% Ae. aegypti) in 8,271 trap-months. Using generalized linear mixed models, we estimated intervention effects on juvenile catch and adult emergence while adjusting for dwelling-level clustering, unequal sampling effort, and weather-related confounders. Following PPF dissemination, Aedes juvenile catch decreased by 79%–92% and juvenile mortality increased from 2%–7% to 80%–90%. Mean adult Aedes emergence fell from 1,077 per month (range 653–1,635) at baseline to 50.4 per month during PPF dissemination (range 2–117). Female Aedes emergence dropped by 96%–98%, such that the number of females emerging per person decreased to 0.06 females per person-month (range 0.002–0.129). Deterministic models predict, under plausible biological-epidemiological scenarios, that the R0 of typical Aedes-borne viruses would fall from 3–45 at baseline to 0.004–0.06 during PPF dissemination. The main limitations of our study were that it was a before–after trial lacking truly independent replicates and that we did not measure mosquito-borne virus transmission empirically.ConclusionsMosquito-disseminated PPF has potential to block mosquito-borne virus transmission citywide, even under adverse scenarios. Our results signal new avenues for mosquito-borne disease prevention, likely including the effective control of Aedes-borne dengue, Zika, and chikungunya epidemics. Cluster-randomized controlled trials will help determine whether mosquito-disseminated PPF can, as our findings suggest, develop into a major tool for improving global public health.

The Zika Virus Epidemic in Brazil: From Discovery to Future Implications

“…Mosquito-disseminated Pyriproxyfen is another novel control strategy being used in Brazil, with promising results regarding the reduction of field populations of Ae. aegypti and the predicted number of dengue cases [ 98 , 99 ].…”

New approaches for integrated and cost-effective malaria vector control

“…Furthermore, the use of growth regulators is not limited to the administration to breeding sites but can be extended to adult vector control in integrated approaches. Insect growth regulators are available for different modes of application, ranging from time release granules to powders and have recently been used at large scale to curb the zika epidemic in Brazil 31 .…”

Resurgence of yellow fever in Brazil: Overview and possible control options

“…Another novel strategy involving infection of A. aegypti with Wolbachia bacteria [9] has revealed remarkable decline in transmission capability of A. aegypti for range of arboviral infection including yellow fever. Recently, a similar study [10] revealed striking outcomes of pyriproxyfen (synthetic analogue of insect juvenile hormone) in curtailing the transmission capacity of A. aegypti. From the preliminary trials and studies on Figure 1.…”