St. Louis encephalitis virus is a complex zoonoses. In 2005, 47 laboratory-confirmed and probable clinical cases of SLEV infection were reported in Córdoba, Argentina. Although the causes of 2005 outbreak remain unknown, they might be related not only to virological factors, but also to ecological and environmental conditions. We hypothesized that one of the factors for SLE reemergence in Córdoba, Argentina, was the introduction of a new SLEV genotype (SLEV genotype III), with no previous activity in the area. In order to evaluate this hypothesis we carried out a molecular characterization of SLEV detections from mosquitoes collected between 2001 and 2004 in Córdoba city. A total of 315 mosquito pools (11,002 individuals) including 12 mosquitoes species were analyzed. Overall, 20 pools (8 mosquitoes species) were positive for SLEV. During this study, genotypes II, V and VII were detected. No mosquito pool infected with genotype III was detected before the 2005 outbreak. Genotype V was found every year and in the 8 sampled sites. Genotypes II and VII showed limited temporal and spatial activities. We cannot dismiss the association of genotype II and V as etiological agents during the outbreak. However, the silent circulation of other SLEV strains in Córdoba city before the 2005 outbreak suggests that the introduction of genotype III was an important factor associated to this event. Not mutually exclusive, other factors such as changes in avian hosts and mosquitoes vectors communities, driven by climatic and environmental modifications, should also be taken into consideration in further studies.

In Argentina, more than 25,000 cases of dengue were reported in the summer of 2009, even The domestic mosquito Aedes aegypti is the primary vector of dengue, the most important vector-borne arbovirosis in the world. Since vaccines against dengue are not yet available, vector monitoring and control are the only present options for the prevention of outbreaks. Currently, chemical treatment is one of the most important components in an integrated campaign (WHO 2000). In 1986, Ae. aegypti re-invaded the northern and central provinces of Argentina, reaching infestation levels even higher than those previously observed in periods prior to the termination of the control campaign in 1964 (Carbajo et al. 2001). In 1997, dengue was reintroduced in Argentina by infected persons with travel histories to Brazil, Ecuador and Venezuela (Avilés et al. 1999) and outbreaks were confirmed in northern provinces close to endemic countries (Salta, Jujuy, Misiones, Formosa and Corrientes), resulting in about 4,700 dengue cases until 2007 (Vezzani & Carbajo 2008 containers are treated with temephos, an internationallyused organophosphorus larvicide (focal treatment), and a new cis-permethrin ultra low volume formulation (Seccacini et al. 2006) is employed as an adulticide in the event of an outbreak (spatial treatment).Susceptibility levels to insecticides used on Ae. aegypti must be constantly screened in different geographical areas to develop successful control strategies because artificial selection of resistant mosquito lines could result in control failures (WHO 1995). Biber et al. (2006) detected differences in resistance levels of Ae. aegypti to temephos [Abate 1G (1%)] in four natural Argentinean subpopulations previously identified by their different haplotypes. Moreover, temporal variation of larval susceptibility to temephos was analysed in Clorinda and Iguazú between 2004 and summer 2006 through summer 2007 and a weak augmentation in the resistance levels to the larvicide was observed in both cities. The resistance ratio (RR) values obtained in that study (3.099 for Clorinda and 3.057 for Iguazú) indicated an incipient resistance and no control failures were detected (Seccacini et al. 2008).To advance understanding of the resistance of Argentinian Ae. aegypti to temephos, we determined the susceptibility levels of individuals from seven populations collected during summer 2007 through summer 2008.Samples were collected in seven cities (Clorinda, 25º17'S 57º43'W, Formosa Province; Iguazú, 25º36'S 54º34'W, Misiones Province; Puerto Rico, 26º47'S 55º02'W, Misiones Province; Orán, 23º08'S 64º19'W, Salta Province; Ledesma, 23º49'S 64º47'W, Jujuy Province; Chepes, 31º20'S 66º35'W, La Rioja Province; Cór-doba, 31º24'S 64º10'W) throughout the summer months from December 2007-January 2008 (Fig. 1). Larvae were taken from artificial water containers and eggs were obtained by ovitraps randomly distributed in the sampled cities, except in Puerto Iguazú, where ovitraps were located only in the proximity of the national park. In Clori...

Aedes aegypti L. (Diptera, Culicidae) is the main vector of dengue and yellow fever. In Argentina, the species was apparently eradicated approximately in 1964; by 1986, it was reintroduced. To identify different gene pools in geographical populations of the species and to ascertain the possible routes of colonization, we analyzed the diversity of mitochondrial DNA haplotypes in 572 specimens from Argentina and neighboring countries. We found that the restriction fragment length polymorphism-polymerase chain reaction screening of a large DNA fragment including the A+T-rich region was the best strategy to reconstruct the colonization pattern ofAe. aegypti in Argentina. Twenty haplotypes were recognized; levels of genetic similarity varied among populations from different geographical locations. The haplotype network constructed on the basis of genetic distances showed three well differentiated groups. Two of them exhibited a well defined spatial distribution and populations in these groups presented an isolation-by-distance pattern. The persistence of relictual populations after the last eradication campaigns would explain the high levels of haplotype diversity and the presence of exclusive haplotypes in urban centers from northwestern Argentina. Eastern Argentine populations showed one prevalent haplotype, also predominant in Brazil and Paraguay. Our results highlight the need for efficient surveys and control campaigns, given the strong effect of land trade on genetic exchange among mosquito populations from Argentina and neighboring countries where dengue is endemic.

Aedes (Stegomyia) aegypti, the main vector of Dengue and Yellow Fever viruses, is present in all the northern and central provinces of Argentina. During 2009, a Dengue outbreak spread broadly throughout the country, causing 27,752 infections in 13 provinces. In Argentina, little is known about the demographic history of this vector, which suffered a drastic decrease in abundance and distribution during a major control campaign performed in the Americas between 1950 and 1960. With the aim of uncovering the past and present events that determined the present distribution of the genetic variability in Ae. aegypti populations, we analyzed the distribution and abundance of mitochondrial haplotypes obtained by sequencing a 450-bp fragment of the ND5 gene. We detected 14 haplotypes among the sequences of 197 individuals from 22 populations that cover most of the distribution of the species in Argentina; one population from Bolivia and one from Paraguay were also included. A high heterogeneity in the geographical distribution of the genetic polymorphism was observed, with a pattern of isolation by distance in the north-west of Argentina. Haplotypes nested in three haplogroups, representing different colonization events and evolutionary histories in distant geographical areas. North-western and north-eastern populations correspond to independent introduced stocks for which a past fragmentation and rapid restoration from highly polymorphic relicts were inferred. By contrast, a unique genetic variant was detected in the east, probably as the result of a recent re-colonization event after the major control campaign; in this area, the mosquito would have been practically eradicated as a consequence of the continental control campaign.

The complete A+T - rich region of Aedes aegypti mitochondrial DNA has been cloned and sequenced. In Argentinean populations of the species, a polymorphism in the length of the amplified fragment was observed. Nucleotide sequence comparison of the shortest and longest A+T - rich amplified fragments detected revealed the presence of 2 types of tandemly repeated blocks. The size variation observed in natural populations is mainly due to the presence of a variable number of a 181 bp tandem repeat unit, located toward the 12S rRNA gene end. The size of the longest A+T - rich region was of 2070 bp, representing the largest control sequence reported for any mosquito species. Few relevant short blocks of primary-sequence similarity conserved in the control region of mosquitoes and other insects were detected scattered throughout the whole region. Five putative stem-loop secondary structures were found, one of them flanked by conserved sequences described in other insects. Our results suggest that there are no universal models of structure-function relations in the control region of insect mtDNA. In addition, we identified a short A+T - rich variable segment in the Ae. aegyti control region that would be suitable for population genetic studies.