Entomological impact of targeted indoor residual spraying on Aedes aegypti density and age structure Public
Culquichicon, Carlos (Spring 2022)
Published
Abstract
Background:
Targeted indoor residual spraying (TIRS) is an adulticide method of insecticide spraying designed to reduce the time and volume of application, and reaching high efficacy levels when preventatively applied. TIRS have the potential of decreasing Aedes-borne virus transmission by decreasing the density of Aedes aegypti mosquitoes, and shifting the age structure of the treated mosquito population to earlier stages of development. We aimed to study the efficacy of TIRS on female Aedes density, and the physiological age of the mosquito population; and secondarily the proportion of nulliparous, and Aedes-borne virus transmission potential.
Methods:
After 1, 3, and 6 months of TIRS application, we conducted dissections of a random subset of female Aedes routinely collected in entomological surveys of households from a clustered-randomized trial. The Polovodova dissection method was used to identify the number of ovariole dilatations in female Ae. aegypti, and classified the egg development using Christopher’s growth (F1-F2) and germinative (F3-F5) stages. Female Ae. aegypti older than 1 dilatation and germinative stages is a chronological proxy of females with completed extrinsic incubation period (i.e., they have the potential to transmit viruses). Random-effect regression models at the cluster- and household-levels estimated incidence rate ratios for the primary outcomes, and odds ratios for the secondary outcomes in order to determine TIRS efficacy levels.
Results:
A total of 324, 102, and 156 dissections (N=582) were conducted at 1, 3 and 6 months post-TIRS, respectively. During post-1, and post-3 evaluations, TIRS efficacy levels on reducing mean female Ae. aegypti density per cluster were 60%, and 41%, respectively; but 27% in post-6. Consistently, TIRS efficacy on decreasing the number of ovariole dilatations were 43%, and 46% for post-1 and post-3, but 20% during post-6. Regarding the secondary outcomes, TIRS efficacy on diminishing the proportion of nulliparous Ae. aegypti were 37%, and 35% in post-1 and post-3, but 12% in post-6. Distinctly, TIRS efficacy on reducing the proportion of female Ae. aegypti with transmissibility potential were 36%, 37%, and 29% for each post evaluation.
Conclusions:
TIRS consistently reduced the density of female Ae. aegypti and shifted the age structure of the mosquito population towards younger maturation stages, leading to an overall reduction in the presence of female Ae. aegypti with the potential to transmit Aedes-borne viruses.
Table of Contents
1 Introduction 1
2 Methods 2
2.1 Study site 2
2.2 Study design 3
2.3 Data collection 3
2.4 Dissection technique 4
2.5 Directed acyclic graph (DAG) 4
2.6 Measures for analysis 5
2.7 Statistical analysis 5
2.8 Model specification 6
2.9 Weather data 6
2.10 Ethics 6
3 Results 7
4 Discussion 8
5 Conclusions and recommendations 10
6 References 11
7 Tables 14
8 Figures 25
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