key: cord-0299296-48q2e372
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.
title: A decade of arbovirus emergence in the temperate southern cone of South America: dengue, Aedes aegypti and climate dynamics in Córdoba, Argentina
date: 2020-07-14
journal: bioRxiv
DOI: 10.1101/2020.01.16.908814
sha: 7218273900371022a18c28b7a8fac9adacd60d7d
doc_id: 299296
cord_uid: 48q2e372

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.

randomly selected 6 neighborhoods, and the field technicians randomly selected 20 181 homes to be inspected per neighborhood. 182

At each home, an inspector noted all containers inside and outside the home with 183 standing water. Inspectors noted the presence of juvenile mosquitoes and collected 184 specimens for species identification. Whenever possible, all juvenile mosquitoes were 185 collected; for large containers where it was not possible to collect all specimens, an 186 inspector collected three samples using a white dipper (62 ml volume). Specimens were 187 transported to the CIEC laboratory. Pupae were reared to adults, and 3 rd and 4 th instar 188 larvae were preserved in 80% ethanol and were identified using taxonomic keys (Darsie 189 Jr, 1985) . First and 2 nd instar larvae were reared until reaching the 3 rd instar in plastic 190 trays with 500 ml of water from the natural larval habitat or dichlorine water. Each day 191 larvae were fed 0.25 mg of liver powder per larva, and we cleaned the surface of the 192 water using absorbent paper to avoid contamination by fungi and/or bacteria. We assumed a unidirectional temporal relationship between the variables as 253 follows: climate affecting all other variables, Ae. aegypti eggs affecting Ae. aegypti 254 larvae and dengue incidence, and Ae. aegypti larvae variables affecting dengue incidence. 255

Both autochthonous and imported cases were included in the analysis. To examine the 256 correlations between these variables, cross-correlation functions were calculated between 257 differenced monthly summary data for each variable with lags up to two months. We 258 selected this period as it is a biologically plausible period of time that includes the 259 combined time for Ae. aegypti egg hatching and larval development to adult mosquitoes. 260

the winter months (June to September), where winter was sampled in 2010 only. There 264 was a notable increase in Ae. aegypti larval abundance over the study period 

The results of the seasonal analysis for climate, mosquito abundance, and dengue 320 incidence variables are presented in Supplemental Table 2 . All climate variables were 321 found to have a 12-month periodicity with nonlinear interannual variability, except for 322 minimum relative humidity, which had no interannual variability, and maximum relative 323 humidity, which had no periodicity nor interannual variability (i.e. temporal trend). The 324 detection of temporal trends can be limited with shorter sets of time series data. 325 peaked approximately twice per year and annually. Imported dengue incidence peaked 340 approximately every 1.5 and 3 years. There was no interannual variability in 341 autochthonous or imported dengue incidence. 342

The results of the cross-correlation between Ae. aegypti eggs and larval 344 abundance, climate, and dengue incidence variables are shown in Table 1 maximum temperature at lag 2, and negatively correlated with total precipitation in the 355 same month, with no correlation to any relative humidity variables. Autochthonous 356 dengue incidence was not correlated with Ae. aegypti egg abundance. Aedes aegypti 357 larvae abundance (percent of neighborhoods with larval presence) was negatively 358 correlated with autochthonous dengue incidence at lag 1. 359 

Arbovirus emergence in temperate climates: the 605 case of

Dengue Vector Dynamics (Aedes aegypti) Influenced by Climate and Social 609 Factors in Ecuador: Implications for Targeted Control

Relationship between

Breteau and House indices and cases of dengue/dengue hemorrhagic fever in