Direct and indirect entomological efficacy of Targeted Indoor Residual Spraying against Aedes aegypti in Iquitos, Peru
6 affiliations
- 1Department of Entomology, U.S. Naval Medical Research Unit SOUTH, Bellavista, Peru
- 2Culmen International, Alexandria, Virginia, United States of America
- 3Dirección Ejecutiva de Salud Ambiental, Gerencia Regional de Salud Loreto, Iquitos, Peru
- 4Department of Pathology, Microbiology, and Immunology, University of California Davis School of Veterinary Medicine, Davis, California, United States of America
- 5Department of Environmental Sciences, Emory University, Atlanta, Georgia United States of America
- 6Navy and Marine Corps Force Health Protection Command, Portsmouth, Virginia, United States of America
Abstract
Background: Control of Aedes aegypti, the primary vector of dengue and other Aedes-borne viruses, is challenged by insecticide resistance, limited efficacy of existing tools, and that control activities often occur in the context of large dengue epidemics that overwhelm control programs. Targeted Indoor Residual Spraying (TIRS), a modification of traditional indoor residual spraying focused on Ae. aegypti resting sites, has demonstrated promising results, yet its indirect community-wide effects remain underexplored. Methodology/principal findings: We conducted an entomological cluster-randomized controlled trial in Iquitos, Peru, to evaluate the direct and indirect entomological impacts of TIRS using pirimiphos-methyl. Thirty clusters were randomized to receive either TIRS (15 clusters, 898 structures) or standard Ministry of Health vector control activities (15 clusters, 1,018 structures). Aedes aegypti indoor densities were assessed in the 45 days pre-intervention and at four time points up to 255 days post-intervention using Prokopack aspiration. Generalized linear mixed models with a negative binomial link were used to estimate incidence rate ratios (IRRs) and calculate efficacy (1–IRR) for houses that received TIRS (direct effect) and untreated houses in TIRS clusters (indirect effect). Direct efficacy reached a 96% decrease in Ae. aegypti captured in sprayed houses at 15 days post-spraying and remained significant (40%) at 255 days post-spraying. Indirect efficacy reached 69% at 15 days and declined to 7% by 255 days post-spraying. Despite only 57% household-level TIRS coverage, both direct and indirect impacts on Ae. aegypti were significant during early post-intervention surveys, and after 8 months in TIRS clusters. Conclusions/significance: TIRS provided substantial and sustained reductions in indoor Ae. aegypti density, including measurable indirect effects in untreated homes within intervention clusters. These findings demonstrate the entomological value of TIRS even at moderate coverage levels and highlight its potential for both preventive and reactive vector control programs and should be considered for implementation by Ministries of Health in dengue-endemic urban settings as well as by the U.S. military when deployed to tropical or subtropical locations. Author summary: Dengue, chikungunya, and Zika are all diseases transmitted by the vector mosquito Aedes aegypti, and the most important tool to combat these diseases is mosquito control. There are many challenges limiting existing methods and a new tool called Targeted Indoor Residual Spraying (TIRS), which is a modification of traditional indoor residual spraying focused on Ae. aegypti resting sites, have demonstrated promising results. Yet we do not know if unsprayed houses benefit indirectly from community-wide effects of the sprayed houses. We conducted a study in Iquitos, Peru, to evaluate the direct and indirect impacts of TIRS (using pirimiphos-methyl) on Ae. aegypti numbers. Thirty clusters of houses received either TIRS (15 clusters, 898 structures) or standard Ministry of Health vector control activities (15 clusters, 1,018 structures). Aedes aegypti numbers inside houses were counted before conducting TIRS and at about 1 week, 1 month, 6 month, and 8 months after. We calculated the reduction in mosquitoes for houses that received TIRS (direct effect) and untreated houses (indirect effect). The direct effect reached a 96% decrease in Ae. aegypti captured in sprayed houses at 15 days post-spraying and remained significant (40%) at 255 days (8 months) post-spraying. The indirect effect reached 69% at 15 days and declined to 7% by 255 days (8 months) post-spraying. Despite only 57% household-level TIRS coverage, both direct and indirect impacts on Ae. aegypti were significant during post-TIRS surveys. TIRS provided substantial and sustained reductions in indoor Ae. aegypti density, including measurable indirect effects in untreated homes within intervention clusters. These findings demonstrate the value of TIRS even at moderate coverage levels and highlight its potential for both preventive and reactive vector control programs and should be considered for implementation by Ministries of Health in dengue-endemic urban settings as well as by the U.S. military when deployed to tropical or subtropical locations.
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BibTeX
@article{astete2026direct,
title = {{Direct and indirect entomological efficacy of Targeted Indoor Residual Spraying against Aedes aegypti in Iquitos, Peru}},
author = {Helvio Astete and Gissella M. Vasquez and Victor M. López-Sifuentes and Beyquer Zambrano and Becker Reyna and Ryan C. Moore and Amy C. Morrison and Gonzalo M. Vazquez-Prokopec and Ryan T. Larson},
journal = {PLOS Neglected Tropical Diseases},
year = {2026},
month = oct,
doi = {10.1371/journal.pntd.0014390},
url = {https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014390},
note = {CC0},
}
RIS
TY - JOUR
TI - Direct and indirect entomological efficacy of Targeted Indoor Residual Spraying against Aedes aegypti in Iquitos, Peru
AU - Helvio Astete
AU - Gissella M. Vasquez
AU - Victor M. López-Sifuentes
AU - Beyquer Zambrano
AU - Becker Reyna
AU - Ryan C. Moore
AU - Amy C. Morrison
AU - Gonzalo M. Vazquez-Prokopec
AU - Ryan T. Larson
PY - 2026
DA - 2026/10/21
JO - PLOS Neglected Tropical Diseases
DO - 10.1371/journal.pntd.0014390
UR - https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014390
AB - Background: Control of Aedes aegypti, the primary vector of dengue and other Aedes-borne viruses, is challenged by insecticide resistance, limited efficacy of existing tools, and that control activities often occur in the context of large dengue epidemics that overwhelm control programs. Targeted Indoor Residual Spraying (TIRS), a modification of traditional indoor residual spraying focused on Ae. aegypti resting sites, has demonstrated promising results, yet its indirect community-wide effects remain underexplored. Methodology/principal findings: We conducted an entomological cluster-randomized controlled trial in Iquitos, Peru, to evaluate the direct and indirect entomological impacts of TIRS using pirimiphos-methyl. Thirty clusters were randomized to receive either TIRS (15 clusters, 898 structures) or standard Ministry of Health vector control activities (15 clusters, 1,018 structures). Aedes aegypti indoor densities were assessed in the 45 days pre-intervention and at four time points up to 255 days post-intervention using Prokopack aspiration. Generalized linear mixed models with a negative binomial link were used to estimate incidence rate ratios (IRRs) and calculate efficacy (1–IRR) for houses that received TIRS (direct effect) and untreated houses in TIRS clusters (indirect effect). Direct efficacy reached a 96% decrease in Ae. aegypti captured in sprayed houses at 15 days post-spraying and remained significant (40%) at 255 days post-spraying. Indirect efficacy reached 69% at 15 days and declined to 7% by 255 days post-spraying. Despite only 57% household-level TIRS coverage, both direct and indirect impacts on Ae. aegypti were significant during early post-intervention surveys, and after 8 months in TIRS clusters. Conclusions/significance: TIRS provided substantial and sustained reductions in indoor Ae. aegypti density, including measurable indirect effects in untreated homes within intervention clusters. These findings demonstrate the entomological value of TIRS even at moderate coverage levels and highlight its potential for both preventive and reactive vector control programs and should be considered for implementation by Ministries of Health in dengue-endemic urban settings as well as by the U.S. military when deployed to tropical or subtropical locations. Author summary: Dengue, chikungunya, and Zika are all diseases transmitted by the vector mosquito Aedes aegypti, and the most important tool to combat these diseases is mosquito control. There are many challenges limiting existing methods and a new tool called Targeted Indoor Residual Spraying (TIRS), which is a modification of traditional indoor residual spraying focused on Ae. aegypti resting sites, have demonstrated promising results. Yet we do not know if unsprayed houses benefit indirectly from community-wide effects of the sprayed houses. We conducted a study in Iquitos, Peru, to evaluate the direct and indirect impacts of TIRS (using pirimiphos-methyl) on Ae. aegypti numbers. Thirty clusters of houses received either TIRS (15 clusters, 898 structures) or standard Ministry of Health vector control activities (15 clusters, 1,018 structures). Aedes aegypti numbers inside houses were counted before conducting TIRS and at about 1 week, 1 month, 6 month, and 8 months after. We calculated the reduction in mosquitoes for houses that received TIRS (direct effect) and untreated houses (indirect effect). The direct effect reached a 96% decrease in Ae. aegypti captured in sprayed houses at 15 days post-spraying and remained significant (40%) at 255 days (8 months) post-spraying. The indirect effect reached 69% at 15 days and declined to 7% by 255 days (8 months) post-spraying. Despite only 57% household-level TIRS coverage, both direct and indirect impacts on Ae. aegypti were significant during post-TIRS surveys. TIRS provided substantial and sustained reductions in indoor Ae. aegypti density, including measurable indirect effects in untreated homes within intervention clusters. These findings demonstrate the value of TIRS even at moderate coverage levels and highlight its potential for both preventive and reactive vector control programs and should be considered for implementation by Ministries of Health in dengue-endemic urban settings as well as by the U.S. military when deployed to tropical or subtropical locations.
SN - 1935-2735
SN - 1935-2727
ER -