Management of vector population is a commonly used method for mitigating transmission of mosquito-borne infections, but quantitative information on its practical public health impact is scarce. We study the effectiveness of Ultra-Low Volume (ULV) insecticide spraying in public spaces for preventing secondary dengue virus (DENV) cases in Porto Alegre, a non-endemic metropolitan area in Brazil. We developed a stochastic transmission model based on detailed entomological, epidemiological and population data, accounting for the geographical distribution of mosquitoes and humans in the study area and spatial transmission dynamics. The model was calibrated against the distribution of DENV cluster sizes previously estimated from the same geographical setting. We estimated a ULV-induced mortality of 40% for mosquitoes and found that the implemented control protocol avoided about 24% of symptomatic cases occurred in the area throughout the 2015-2016 epidemic season. Increasing the radius of treatment or the mortality of mosquitoes by treating gardens and/or indoor premises would greatly improve the result of control, but trade-offs with respect to increased efforts need to be carefully analyzed. We found a moderate effectiveness for ULV-spraying in public areas, mainly due to the limited ability of this strategy in effectively controlling the vector population. These results can be used to support the design of control strategies in low-incidence, non-endemic settings. Author summary Dengue is a mosquito-borne infection that causes millions of symptomatic infections and thousands of deaths per year. This pathogen is expanding its geographic range to areas that were previously free from autochthonous transmission thanks to the intensification of international travels, urbanization and to climatic adaptation of mosquitoes and viruses. Usually interventions against dengue transmission consist in insecticide spraying aimed at killing adult mosquitoes, but the impact of this practice has been rarely evaluated in real-life settings. In this work, we estimate the proportion of dengue cases avoided by Ultra-Low-Volume insecticide spraying in public areas in Porto Alegre (Brazil). This city is characterized by a subtropical climate, negligible pre-existing immunity and low dengue incidence. The low incidence makes this region unsuitable for deployment of the currently licensed vaccine, which is only recommended by the WHO for high-transmission areas. We found that insecticide spraying avoided approximately one fourth of all symptomatic cases. The performance of the intervention was negatively affected by the low treatment-induced mosquito mortality, as we estimated that only 40% of Ae. aegypti are killed by the insecticide. Control outcomes could be improved by increasing the targeted area and including private premises, but trade-offs against increased efforts need to be carefully analyzed.
Marini, G; Guzzetta, G; Toledo, CAM; Teixeira, M; Rosà, R; Merler, S
Effectiveness of Ultra-Low Volume insecticide spraying to prevent dengue in a non-endemic metropolitan area of Brazil
Plos Computational Biology