Dengue vector dynamics (Aedes aegypti) influenced by climate and social factors in Ecuador: implications for targeted control

Abstract

Background: Dengue fever, a mosquito-borne viral disease, is now the fastest spreading tropical disease globally. Previous studies indicate that climate and human behavior interact to influence dengue virus and vector (Aedes aegypti) population dynamics; however, the relative effects of these variables depends on local ecology and social context. We investigated the roles of climate and socio-ecological factors on Ae. aegypti population dynamics in Machala, a city in southern coastal Ecuador where dengue is hyper-endemic.

Methods/principal findings: We studied two proximate urban localities where we monitored weekly Ae. aegypti oviposition activity (Nov. 2010-June 2011), conducted seasonal pupal surveys, and surveyed household to identify dengue risk factors. The results of this study provide evidence that Ae. aegypti population dynamics are influenced by social risk factors that vary by season and lagged climate variables that vary by locality. Best-fit models to predict the presence of Ae. aegypti pupae included parameters for household water storage practices, access to piped water, the number of households per property, condition of the house and patio, and knowledge and perceptions of dengue. Rainfall and minimum temperature were significant predictors of oviposition activity, although the effect of rainfall varied by locality due to differences in types of water storage containers.

Conclusions: These results indicate the potential to reduce the burden of dengue in this region by conducting focused vector control interventions that target high-risk households and containers in each season and by developing predictive models using climate and non-climate information. These findings provide the region's public health sector with key information for conducting time and location-specific vector control campaigns, and highlight the importance of local socio-ecological studies to understand dengue dynamics. See Text S1 for an executive summary in Spanish.

Figure 1. Map of study localities.

A map of the districts of the city of Machala, El Oro Province, Ecuador, indicating the location of the study areas and the meteorological station.

Figure 2. Climate in Machala, Ecuador.

The climatology of Machala (November to June, 1986–2009 average) compared to the weather during the study period for (A) temperature and (B) monthly rainfall.

Figure 3. Aedes aegypti pupae per container type by location and season.

Percentage of all pupae collected from abandoned, domestic-use, and other types of containers (i.e., decorative, animal drinking water) in pupae surveys conducted during pre-rainy, rainy, and post-rainy seasons in the (A) central study area (CA), (B) peripheral study area (PA), and (C) both localities combined in Machala, Ecuador.

Figure 4. Aedes aegypti oviposition dynamics predicted by lagged local climate.

Time series of observed and predicted (95% CI) log eggs/ovitrap/week over the study period (Nov. 2010 to June 2011) from the best-fit models for the (A) peripheral area (PA) and (B) central area (CA).

Figure 5. Climatic and social factors interact to influence seasonal dengue risk.

A synthesis of the important socio-ecological predictors for the presence of Aedes aegypti during rainy and post-rainy (dry) seasons in Machala, Ecuador.