BACKGROUND

The developing fetuses of pregnant women are at high risk of developing serious birth defects following Zika virus infections. We applied an Integrated Vector Control (IVC) approach using source reduction, larviciding, and mass trapping with non-insecticidal sticky traps to protect targeted houses by reducing the density of female Aedes aegypti mosquitoes.

METHODS

We tested the hypothesis that Ae. aegypti density could be reduced to below three female mosquitoes/trap/week around a target house in the center of a circular area with a 150 m radius using IVC. Two non-adjacent areas within the same neighbourhood were selected and randomly designated as the treatment or control areas. Sentinel Autocidal Gravid Ovitraps (SAGO traps) were placed in each study area and were sampled weekly from May to November, during the 2016 Zika epidemic in Puerto Rico. The experimental design was longitudinal with pre-and post-IVC treatment observations between treatment and control areas, and a partial cross-over design, where IVC was applied to the original control area after 2 months to determine if Ae. aegypti density converged to levels observed in the treatment area. Pools of female Ae. aegypti mosquitoes were analyzed by RT-PCR to detect Zika, dengue and chikungunya virus RNA.

RESULTS

Overall, pre-treatment mosquito densities in the inner (0-50 m; 15.6 mosquitoes/trap/week), intermediate (50-100 m; 18.1) and outer rings (100-150 m; 15.6) were reduced after treatment to 2.8, 4.1, and 4.3 in the inner, middle, and outer rings, respectively. Density at the target house in the treatment area changed from 27.7 mosquitoes/trap/week before IVC to 2.1 after IVC (92.4% reduction), whereas after treating the original control area (cross-over) density changed from 22.4 to 3.5 (84.3% reduction). Vector reductions were sustained in both areas after IVC. Zika virus was detected in Ae. aegypti, but the low incidence of the virus precluded assessing the impact of IVC on Zika transmission during the study.

CONCLUSIONS

Applying IVC to circular areas that were surrounded by untreated areas significantly decreased the number of mosquitoes around target houses located in the center. Gravid Ae. aegypti females in the center of the 150 m areas fell below threshold levels that possibly protect against novel invading arboviruses, such as chikungunya and Zika.