Forecasting the effectiveness of indoor residual spraying for reducing dengue burden

• Type of Material: Article
• Authors: Thomas J. Hladish, University of Florida; Carl A. B. Pearson, Very Good Research & Development; Diana Patricia Rojas, University of Florida; Hector Gomez-Dantes, National Institute of Public Health; M. Elizabeth Halloran, Fred Hutchinson Cancer Research Center; Gonzalo Vazquez Prokopec, Emory University; Ira M. Longini, University of Florida
• Language: English
• Date: 2018-06-25
• Publisher: Public Library of Science
• Publication Version: Final Published Version
• Copyright Statement: © 2018 Hladish et al
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1371/journal.pntd.0006570
• Title of Journal or Parent Work: PLoS Neglected Tropical Diseases
• ISSN: 1935-2727
• Volume: 12
• Issue: 6
• Start Page: e0006570
• End Page: e0006570
• Grant/Funding Information: This project was funded by a National Institutes of Health/National Institute of General Medical Sciences Grant (https://www.nih.gov/; U54 GM111274) to MEH, a National Science Foundation Grant (https://nsf.gov; DEB/EEID: 1640698) to GMVP, and a Fulbright - Colciencias doctoral scholarship (http://www.fulbright.edu.co) to DPR from the Colombian Department of Science and Technology.; The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
• Research Categories: Biology, Biostatistics; Biology, General

Abstract

Background Historically, mosquito control programs successfully helped contain malaria and yellow fever, but recent efforts have been unable to halt the spread of dengue, chikungunya, or Zika, all transmitted by Aedes mosquitoes. Using a dengue transmission model and results from indoor residual spraying (IRS) field experiments, we investigated how IRS-like campaign scenarios could effectively control dengue in an endemic setting. Methods and findings In our model, we found that high levels of household coverage (75% treated once per year), applied proactively before the typical dengue season could reduce symptomatic infections by 89.7% (median of 1000 simulations; interquartile range [IQR]:[83.0%, 94.8%]) in year one and 78.2% (IQR: [71.2%, 88.0%]) cumulatively over the first five years of an annual program. Lower coverage had correspondingly lower effectiveness, as did reactive campaigns. Though less effective than preventative campaigns, reactive and even post-epidemic interventions retain some effectiveness; these campaigns disrupt inter-seasonal transmission, highlighting an off-season control opportunity. Regardless, none of the campaign scenarios maintain their initial effectiveness beyond two seasons, instead stabilizing at much lower levels of benefit: in year 20, median effectiveness was only 27.3% (IQR: [-21.3%, 56.6%]). Furthermore, simply ceasing an initially successful program exposes a population with lowered herd immunity to the same historical threat, and we observed outbreaks more than four-fold larger than pre-intervention outbreaks. These results do not take into account evolving insecticide resistance, thus long-term effectiveness may be lower if new, efficacious insecticides are not developed. Conclusions Using a detailed agent-based dengue transmission model for Yucatán State, Mexico, we predict that high coverage indoor residual spraying (IRS) interventions can largely eliminate transmission for a few years, when applied a few months before the typical seasonal epidemic peak. However, vector control succeeds by preventing infections, which precludes natural immunization. Thus, as a population benefits from mosquito control, it gradually loses naturally acquired herd immunity, and the control effectiveness declines; this occurs across all of our modeled scenarios, and is consistent with other empirical work. Long term control that maintains early effectiveness would require some combination of increasing investment, complementary interventions such as vaccination, and control programs across a broad region to diminish risk of importation.