Marta Gladys Grech

Background: Aedes aegypti is the vector of dengue fever and chikungunya in the city of Córdoba, Argentina, a city situated at the southern limit of disease transmission by the vector in a temperate area. This study aims to characterise the habitat of juvenile Ae. aegypti in households and assess the influence of microenvironmental and environmental variables on its occurrence. Methods: Monthly surveys were conducted from 2019 to 2020 and in 2021 in peridomiciles. Water containers where Ae. aegypti were found were classified according to their material, class and capacity. Using generalised linear mixed models, we evaluated the influence of surrounding vegetation, water container availability and weather conditions (air temperature and precipitation during autumn, summer and spring) on the presence and abundance of juvenile Ae. aegypti . Results: Of the 689 containers surveyed, 109—found in 36.7% (77/210) of the households—contained juvenile Ae. aegypti . Small (1–8 l) and very small (< 0.5 l) containers accounted for 80.4% of the containers positive for juvenile Ae. aegypti , with plastic jars being the most common. Vases and tarpaulins/plastic covers were the most productive containers. Containers shaded by vegetation were 2.5-fold more likely to harbour juveniles than those exposed to sunlight or artificial shade. The strong interaction between tree cover and shade provided by vegetation suggested that vegetation cover enhances mosquito abundance. Juvenile abundance increased with container capacity, while higher precipitation and minimum temperature in the previous weeks also favoured the presence of juveniles. Conclusions: Household containers, which are widely available and diverse in size and material in Córdoba City, provide favourable conditions for the persistence of Ae. aegypti . Abandoned nonfunctional and cryptic sites, such as tarpaulins and plastic covers, can provide breeding sites that enable Ae. aegypti mosquitoes endure the cold and dry seasons. During the warm and wet seasons, the presence and abundance of Ae. aegypti are influenced by microenvironmental conditions, such as shade provided by vegetation, high minimum temperatures and precipitation. The variety and number of available containers, together with shelter and feeding conditions, suggest that female mosquitoes can still find breeding sites even after selective household control measures have been implemented. These results, supported by generalised linear mixed models, which consider the lack of independence between containers within the same household or block, highlight the importance of incorporating fine-scale environmental variables into vector control planning. Graphical

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. 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 the Aedes aegypti mosquito. 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 that Ae. aegypti were 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 with Ae. 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.

Environmental variables are some of the factors that more impact on Aedes aegypti , vector of Dengue, Chikungunya and Zika viruses. In this study, the Ae. aegypti oviposition activity was related to satellite and meteorological variables, in Córdoba City (Argentina). Eggs were collected using ovitraps placed throughout the city from 2009 to 2012, replaced them weekly. Generalized Linear Mixed Models were developed with negative binomial distributions of errors, modeling average number of eggs collected weekly as a function of satellite and meteorological variables with time lags. The best model included a vegetation index, vapor pressure of water, precipitation and photoperiod, lagged between 3 and 4 weeks. By each increment unit in vegetation index, vapor pressure (hPa) and light hour, the average number of eggs increases by 72%, 20% and 29%, respectively, in the following 3 or 4 weeks. In addition, the average number of eggs decreases a 50% in the following month by each millimeter of rain. The results evince the relevant importance of the vegetation, maybe due to the shade that provide to the containers as breeding habitat of this species and the shelter for adults. On the other hand, the negative effect of precipitation could be a consequence of abundant rainfalls that fulfill containers avoiding females to lay eggs in there. Although no significant effect of the photoperiod on the vector abundance has been detected in the north of the country, in Córdoba City an important effect is observed when it is presented together with other variables, producing different effects of these variables in different regions. Lastly, it is necessary to emphasize the importance of the minimum temperature in temperate zones, since it would be a limiting factor that prevents the Ae. aegypti oviposition activity.

The survival of adult female Aedes mosquitoes is a critical component of their ability to transmit pathogens such as dengue viruses. One of the principal determinants of Aedes survival is temperature, which has been associated with seasonal changes in Aedes populations and limits their geographical distribution. The effects of temperature and other sources of mortality have been studied in the field, often via mark-release-recapture experiments, and under controlled conditions in the laboratory. Survival results differ and reconciling predictions between the two settings has been hindered by variable measurements from different experimental protocols, lack of precision in measuring survival of free-ranging mosquitoes, and uncertainty about the role of age-dependent mortality in the field.

The aims of this study were to characterise the ground-level larval habitats of the mosquito Culex quinquefasciatus, to determine the relationships between habitat characteristics and larval abundance and to examine seasonal larval-stage variations in Córdoba city. Every two weeks for two years, 15 larval habitats (natural and artificial water bodies, including shallow wells, drains, retention ponds, canals and ditches) were visited and sampled for larval mosquitoes. Data regarding the water depth, temperature and pH, permanence, the presence of aquatic vegetation and the density of collected mosquito larvae were recorded. Data on the average air temperatures and accumulated precipitation during the 15 days prior to each sampling date were also obtained. Cx. quinquefasciatus larvae were collected throughout the study period and were generally most abundant in the summer season. Generalised linear mixed models indicated the average air temperature and presence of dicotyledonous aquatic vegetation as variables that served as important predictors of larval densities. Additionally, permanent breeding sites supported high larval densities. In Córdoba city and possibly in other highly populated cities at the same latitude with the same environmental conditions, control programs should focus on permanent larval habitats with aquatic vegetation during the early spring, when the Cx. quinquefasciatus population begins to increase.

The presence of Aedes aegypti is reported beyond its current limit of distribution in Argentina, in the city of Neuquén, Neuquén Province. Ovitraps were placed to collect Ae. aegypti eggs between December 2009 and April 2010. The geographical distribution of Culex eduardoi, Psorophora ciliata and Ps. cingulata is extended with new records from two provinces.