Measuring mosquito control: adult-mosquito catches vs egg-trap data as endpoints of a cluster-randomized controlled trial of mosquito-disseminated pyriproxyfen

Abstract

Background: Aedes aegypti and Culex quinquefasciatus are the main urban vectors of arthropod-borne viruses causing human disease, including dengue, Zika, or West Nile. Although key to disease prevention, urban-mosquito control has met only limited success. Alternative vector-control tactics are therefore being developed and tested, often using entomological endpoints to measure impact. Here, we test one promising alternative and assess how three such endpoints perform at measuring its effects. Methods: We conducted a 16-month, two-arm, cluster-randomized controlled trial (CRCT) of mosquito-disseminated pyriproxyfen (MD-PPF) in central-western Brazil. We used three entomological endpoints: adult-mosquito density as directly measured by active aspiration of adult mosquitoes, and egg-trap-based indices of female Aedes presence (proportion of positive egg-traps) and possibly abundance (number of eggs per egg-trap). Using generalized linear mixed models, we estimated MD-PPF effects on these endpoints while accounting for the non-independence of repeated observations and for intervention-unrelated sources of spatial-temporal variation. Results: On average, MD-PPF reduced adult-mosquito density by 66.3% (95% confidence interval, 95% CI: 47.3-78.4%); Cx. quinquefasciatus density fell by 55.5% (95% CI: 21.1-74.8%), and Ae. aegypti density by 60.0% (95% CI: 28.7-77.5%). In contrast, MD-PPF had no measurable effect on either Aedes egg counts or egg-trap positivity, both of which decreased somewhat in the intervention cluster but also in the control cluster. Egg-trap data, therefore, failed to reflect the 60.0% mean reduction of adult Aedes density associated with MD-PPF deployment. Conclusions: Our results suggest that the widely used egg-trap-based monitoring may poorly measure the impact of Aedes control; even if more costly, direct monitoring of the adult mosquito population is likely to provide a much

Large-Scale Deployment of Pyriproxyfen-Treated Lehmann Funnel Entry Traps to Control Malaria Mosquito Populations

“…However, toward the end of the intervention, 12% of the females were scored parous in the control village against ~3% in the intervention village, indicating that the trap was cumulatively extracting and killing old females capable of transmitting malaria in the intervention village. Furthermore, adult dissection results showed that 80% of the females dissected failed to develop their ovaries as previously reported [29,30,47]. That the LFETs were impregnated with PPF increased the performance of the trap by sterilizing any female mosquito that came into contact with the trap net, preventing them from having offspring and consequently decreasing the malaria vectors' population in the village.…”

“…Additionally, traps removed and killed a proportion of older outdoor mosquitoes from the village, which may have impacted on outdoor malaria transmission, as was recently shown in other studies [24,[43][44][45]. Successful implementation of LFET traps as a malaria tool may focus on the direct monitoring of the adult mosquito population, as this provides a realistic picture of the effects of intervention [46,47]. As part of this direct monitoring, the PSC results indicated that traps have signi cantly reduced mosquito population density at the community level in the intervention village VK3, when compared to the control village, VK5.…”

“…Nevertheless, recent studies have demonstrated a PPF sterilizing effect on Aedes spp, and Culex spp etc. when transported and spread by mosquito tarsi to breeding sites [47]. Consequently, this route could have impacted other mosquitoes within and around the LFET trial site.…”

The role and challenges of cluster randomised trials for global health

“…In contrast to the individual RCT, in which the group allocation of interventions is determined by randomisation of individual participants, cluster trials randomly assign interventions to a whole cluster of individuals. Interventions themselves can be administered at a cluster level (eg, mosquito egg traps 5 ) or at an individual level (eg, vaccinations 6 ). In cluster trials, outcomes can be measured at a cluster level 6 or at an individual level.…”

Oviposition dynamics of Aedes aegypti in Central Argentina

“…aegypti eggs or egg positive containers and the adult population size have largely been discounted because of the skip oviposition behaviour of this species. However, recent studies have demonstrated that high adult population abundance increases the probability of collecting eggs (Carbajo et al, 2006;Garcia et al, 2020). The models may also include information about environmental factors important for the life cycle of the species, and this information can be obtained using satellite imagery (Parselia et al, 2019).…”