A decade of arbovirus emergence in the temperate southern cone of South America: dengue,Aedes aegyptiand climate dynamics in Córdoba, Argentina
Authors: Estallo Elizabet L. , Sippy Rachel , Stewart-Ibarra Anna M. , Grech Marta G. , Benitez Elisabet M. , Ludueña-Almeida Francisco F. , Ainete Mariela , Frias-Cespedes María , Robert Michael , Romero Moory M. , Almirón Walter R. 
Published: January 2020

Background

Argentina is located at the southern temperate range of arboviral transmission by the mosquitoAedes aegyptiand 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 ofAe. 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 aegyptiwere 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 juvenileAe. aegyptiover the study period (from 5.7% of homes in 2009-10 to 15.4% of homes in 2016-17).Aedes aegyptieggs 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.

Author summary

There is an increasing risk of arbovirus transmission in temperate regions. Argentina is located at the southern range of dengue virus transmission by theAedes aegyptimosquito. In the last decade, epidemics of dengue fever have emerged for the first time in the city of Córdoba, Argentina. We present the study design and findings from an entomological surveillance study in Córdoba, which began following the emergence of dengue in 2009. We found thatAe. aegyptiwere most abundant from January to March, followed by a peak in local dengue transmission in April. Over the study period, we noted a considerable increase in the proportion of homes withAe. aegypti. Vector indices were positively associated with warmer temperatures, which have been increasing in this region. However, the timing of local dengue transmission appears to be driven by the appearance of imported dengue cases associated with human movement. These results highlight the important role of long term surveillance studies in areas of disease emergence.