Optimizing the deployment of ultra-low volume and indoor residual spraying for dengue outbreak response

Abstract

Recent years have seen rising incidence of dengue and large outbreaks of Zika and chikungunya, which are all caused by viruses transmitted by Aedes aegypti mosquitoes. In most settings, the primary intervention against Aedes-transmitted viruses is vector control, such as indoor, ultra-low volume (ULV) spraying. Targeted indoor residual spraying (TIRS) has the potential to more effectively impact Aedes-borne diseases, but its implementation requires careful planning and evaluation. The optimal time to deploy these interventions and their relative epidemiological effects are not well understood, however. We used an agent-based model of dengue virus transmission calibrated to data from Iquitos, Peru to assess the epidemiological effects of these interventions under differing strategies for deploying them. Specifically, we compared strategies where spray application was initiated when incidence rose above a threshold based on incidence in recent years to strategies where spraying occurred at the same time(s) each year. In the absence of spraying, the model predicted 361,000 infections [inter-quartile range (IQR): 347,000 - 383,000] in the period 2000-2010. The ULV strategy with the fewest median infections was spraying twice yearly, in March and October, which led to a median of 172,000 infections [IQR: 158,000 - 183,000] over the 11-year study period, a 52% reduction from baseline. Compared to spraying once yearly in September, the best threshold-based strategy utilizing ULV had fewer median infections (254,000 vs. 261,000), but required more spraying (351 vs. 274 days). For TIRS, the best strategy was threshold-based, which led to the fewest infections of all strategies tested (9,900; [IQR: 8,720 - 11,400], a 94% reduction), and required fewer days spraying than the equivalent ULV strategy (280). Although spraying twice each year is likely to avert the most infections, our results indicate that a threshold-based strategy can become an alternative to better balance the translation of spraying effort into impact, particularly if used with a residual insecticide.

The TIRS trial: protocol for a cluster randomized controlled trial assessing the efficacy of preventive targeted indoor residual spraying to reduce Aedes-borne viral illnesses in Merida, Mexico

“…Fitting such entomological information to an agent-based model of Yucatan State, Mexico, showed that high levels of TIRS coverage (75% of houses treated once per year) applied preemptively before the typical dengue season (before July) could reduce DENV infections by 89.7% in year 1 and 78.2% cumulatively over the first 5 years of an annual program [32]. Such findings were confirmed with another modeling study comparing TIRS with indoor space spraying in Iquitos, Peru [33]. These findings suggest that preemptive TIRS may provide high short-term and long-term effectiveness in preventing ABVs in endemic areas where transmission is seasonal.…”

“…The doctor will be joined by one field team member, who will obtain demographic and behavioral data, and collect blood specimens. Acute and convalescent (obtained 28 [range [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] days after symptom onset) blood specimens will be collected from each suspected case to confirm ABV infection. Additionally, history of movement (by a retrospective movement survey) [16,52] will provide information on potential exposure locations for each case.…”

Rapid Evolution of Knockdown Resistance Haplotypes in Response to Pyrethroid Selection inAedes aegypti

“…During the past two decades, researchers have preserved mosquito specimens collected throughout the city of Iquitos (e.g. Cavany et al, 2020;Cromwell et al, 2017;Getis et al, 2003;Gunning et al, 2018;LaCon et al, 2014;Lenhart et al, 2020;Morrison et al, 2004a;Morrison et al, 2004b;Morrison et al, 2006;Morrison et al, 2008;Reiner et al, 2019;Schneider et al, 2004;Tun-Lin et al, 2009). Prior to 2002, no citywide insecticide spraying occurred.…”

Residual efficacy of the neonicotinoid insecticide clothianidin against pyrethroid‐resistant Aedes aegypti

“…9,10 Mathematical models also predicted strong and sustained reductions in Ae. aegypti and ABV transmission 11,12 and showed that greater epidemiological efficacy can be achieved as the insecticide residual efficacy increases. 13 TIRS expansion, adoption, and sustainability to the emergence of insecticide resistance will depend on the availability of insecticide molecules and formulations with high residual capacity and to which mosquitoes are susceptible.…”