A decade of arbovirus emergence in the temperate southern cone of South America: dengue, Aedes aegypti and climate dynamics in Córdoba, Argentina

Abstract

Background: Argentina is located at the southern temperate range of arboviral transmission by the mosquito Aedes aegypti and has experienced a rapid increase in disease transmission in recent years. Here we present findings from an entomological surveillance study that began in Córdoba, Argentina, following the emergence of dengue in 2009.

Methods: From 2009 to 2017, larval surveys were conducted monthly, from November to May, in 600 randomly selected households distributed across the city. From 2009 to 2013, ovitraps (n = 177) were sampled weekly to monitor the oviposition activity of Ae. aegypti. We explored seasonal and interannual dynamics of entomological variables and dengue transmission. Cross correlation analysis was used to identify significant lag periods.

Results: Aedes aegypti were detected over the entire study period, and abundance peaked during the summer months (January to March). We identified a considerable increase in the proportion of homes with juvenile Ae. aegypti over the study period (from 5.7% of homes in 2009-10 to 15.4% of homes in 2016-17). Aedes aegypti eggs per ovitrap and larval abundance were positively associated with temperature in the same month. Autochthonous dengue transmission peaked in April, following a peak in imported dengue cases in March; autochthonous dengue was not positively associated with vector or climate variables.

Conclusions: This longitudinal study provides insights into the complex dynamics of arbovirus transmission and vector populations in a temperate region of arbovirus emergence. Our findings suggest that Córdoba is well suited for arbovirus disease transmission, given the stable and abundant vector populations. Further studies are needed to better understand the role of regional human movement.

Keywords: Aedes aegypti; Argentina; Climate; Dengue; Environmental analysis; Environmental science; Epidemiology; Infectious disease; Larval surveys; Ovitrap; Surveillance; Zoology.

Figure 1

Location of Córdoba in South America. The location of Córdoba Province (dark purple) shown within the country of Argentina (light purple), with an inset map showing the city of Córdoba, the location of this study, with roads in grey and waterways in blue. Note that Córdoba is located in the temperate southern cone of South America.

Figure 2

Time series of monthly dengue, Aedes aegypti larval and Ae. aegypti eggs abundance. Top: Dengue cases. Center: proportion of homes with Ae. aegypti larvas. Bottom: proportion of ovitraps (N = 177) positive for Ae. aegypti and the mean number of eggs per ovitrap.

Figure 3

Times series of monthly climate variables. Mean monthly temperatures (°Celsius) are in the top panel (red) (minimum and maximum in dashed lines), total monthly precipitation (mm) is in the central panel (blue) and mean monthly relative humidity (percentage) is in the bottom panel (green) (minimum and maximum in dashed lines).

Figure 4

Seasonal and annual Aedes aegypti egg counts and positivity from ovitraps (2009–2013). Box and whisker plots show the monthly (left) and annual (right) median and quartiles of Ae. aegypti eggs counts and positivity of ovitraps distributed across the city of Córdoba from 2009 to 2013. Note that ovitraps were sampled during the winter months (June to September) only in 2010. Annual averages calculated using data collected during the sampling season (November–May) each year, from 2009 to 2013. Top: Number of Ae. aegypti eggs collected per ovitrap (left) or per ovitrap per annual sampling season (right). Bottom: The percent of ovitraps with Ae. aegypti eggs (left) or per annual sampling season (right).

Figure 5

Seasonal and annual Aedes aegypti larval abundance from household larval surveys (2009–2017). Box and whisker plots show the monthly (left) and annual (right) median and quartiles of Ae. aegypti larval abundance from household larval surveys conducted in households in Córdoba from 2009 to 2017. Annual averages were calculated using data collected during the sampling season each year (November–May). Top: Percent of homes with water-bearing containers with juvenile Ae. aegypti. Bottom: Percent of neighborhoods with water-bearing containers with juvenile Ae. aegypti.

Figure 6

Seasonal and annual imported and autochthonous dengue cases in the city of Córdoba (2009–2017). Box and whisker plots (left) show the monthly median and quartiles of dengue cases reported in Córdoba from 2009 to 2017. Annual (right) imported and autochthonous dengue cases in Córdoba as reported by the Ministry of Health from 2009 to 2017. Top: Total annual reported autochthonous dengue cases (no travel history). Bottom: Total annual imported dengue cases.