Exploring the range of Culex mosquitoes in Western Argentinean Patagonia, unveiling the presence of Culex pipiens bioform pipiens in South America.

Culicids in Argentinean Patagonia are characterized by low species diversity and adaptation to extreme environmental conditions, yet few studies have been conducted in the region. To further assess the occurrence of Culicidae in Western Patagonia, and in particular the presence of Culex pipiens bioforms at the southernmost extent of their distribution, immature and adult specimens were collected aboveground across various land uses located in shrubland, steppe, and deciduous forest between 38.96 and 46.55°S. Mosquitoes were reported at 35 of the 105 inspected sites. Five species from the genus Culex were identified, all of which were present in the steppe and the forest, while only Cx. apicinus and members of the Cx. pipiens complex were collected in the shrubland. Within the latter, a total of 150 specimens were molecularly identified by PCR amplification of Ace-2 and CQ11 loci. The first-to-date occurrence of bioform pipiens in South America is reported, along with the first records of Cx. quinquefasciatus signatures in Patagonia. In addition, the distribution of Cx. acharistus and Cx. dolosus as south as Santa Cruz province is expanded, and the first record of Cx. eduardoi in Río Negro province is provided. Immature specimens of Cx. pipiens were conspicuous in human-made aquatic habitats (both containers and in the ground), while Cx. acharistus was more prominent in artificial containers and Cx. eduardoi was mainly in ground habitats, either natural or human-made. These findings provide valuable insights into the distribution and ecological roles of these mosquito species in a region of extreme environmental conditions.

Blood feeding patterns of the Culex pipiens complex in equestrian land uses and their implications for arboviral encephalitis risk in temperate Argentina.

Blood feeding patterns of mosquitoes are a key component in the dynamics of arboviral encephalitides transmission. In temperate Argentina, the members of the Culex pipiens complex include Cx. pipiens molestus, Cx. quinquefasciatus and their hybrids. To characterize their blood feeding patterns, adult resting mosquitoes were collected monthly during the warm season in urban and rural equestrian fields. The availability of birds and domestic mammals per site was characterized. The blood source and the complex member were successfully identified for 89 specimens using PCR. Blood of 19 vertebrate species was isolated including four mammals (most common feeds from dog, Canus lupus 19% of the blood meals; and horse, Equus caballus 18%) and 15 birds (picazuro pigeon, Patagioenas picazuro 11%; eared dove, Zenaida auriculata 10%; chicken, Gallus gallus 9%). The Forage Ratio (FR), calculated as the proportion of feeds taken from a given host species with respect to that host availability in the environment, suggested preference for dog by all members of the complex (FR ≥4.5). On the contrary, FR values suggested avoidance for horse by Cx. quinquefasciatus and the hybrid (FR ≤0.8), and a use proportional to its abundance by Cx. pipiens molestus (FR = 1.1-1.2 in urban and rural sites, respectively). FR values suggesting preference were obtained for avian species of the orders Passeriformes (7 species in total) and Columbiformes (5) by all members of the complex (FR ≥ 3.3), whereas values for monk parakeet (Myiopsitta monachus, Psiitaciformes) suggested avoidance by Cx. quinquefasciatus in urban sites (FR = 0.4) and by Cx. pipiens molestus in rural sites (FR = 0.3) but not in urban sites (FR = 1.4). A mammal-bird index (MBI, from -1 all avian to +1 all mammalian blood meals) was calculated for each member of the complex and urbanization category. Values were negative for Cx. quinquefasciatus (MBIurban  = -0.60, MBIrural  = -0.33) and positive for Cx. pipiens molestus (MBIurban  = 0.20, MBIrural  = 0.60), indicating a higher proportion of feeds taken on birds and mammals, respectively, regardless of the urbanization category. In temperate Argentina, the members of the Cx. pipiens complex fed both on horses and on birds, thus representing a real risk of transmission of arboviral encephalitides from avian enzootic cycles to horse epizootics.

Aedes aegypti spreading in South America: new coldest and southernmost records.

The geographic distribution of Aedes (Stegomyia) aegypti (L.) in South America has been expanding during the last decades. Herein we present two new distribution records that extend its southern limits towards localities with extremer environmental conditions than reported to date. San Antonio Oeste constitutes the southernmost finding for the continent (40º44'S), whereas Tandil is the infested locality with the coldest mean annual temperature in Argentina (14.17ºC). The projection of a previous distribution model for Ae. aegypti predicts these two cities as positive and suggests several other localities with suitable conditions for vector proliferation beyond its assumed distribution limits.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit.

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Soil presence reduces the control effectiveness of a slow-release formulation of pyriproxyfen on Aedes aegypti (Diptera: Culicidae) larvae.

OBJECTIVE: To assess the influence of soil on the effectiveness of two new slow-release formulations (floating and non-floating) of pyriproxyfen coextruded with low-density polyethylene. METHODS: Two slow-release devices were developed using low-density polyethylene, pyriproxyfen as larvicide and calcium carbonate as filler. A factorial design was used to evaluate the effect of soil presence on the performance of each device. Weekly bioassays were performed. RESULTS: Soil presence affected treatment effectiveness, but this effect was associated with device type. The tablets were effective for nearly 3 months. CONCLUSION: Treatment effectiveness could be reduced because of the loss of pyriproxyfen by several physico-chemical processes such as adsorption into the soil.

OBJECTIF: Evaluer l'influence de la terre sur l'efficacité de deux nouvelles formulations à libération lente (flottante et non flottante) de pyriproxyfène coextrudé avec du polyéthylène de faible densité. MÉTHODES: Deux dispositifs à libération lente ont été développés en utilisant du polyéthylène de faible densité, du pyriproxyfène comme larvicide et du carbonate de calcium comme agent de charge. Un plan factoriel a été utilisé pour évaluer l'effet de la présence de terre sur les performances de chaque dispositif. Des essais biologiques hebdomadaires ont été effectués. RÉSULTATS: La présence de terre a affecté l'efficacité du traitement, mais cet effet était associé au type de dispositif. Les comprimés ont été efficaces pendant près de 3 mois. CONCLUSION: L'efficacité du traitement pourrait être réduite en raison de la perte du pyriproxyfène par plusieurs processus physicochimiques tels que l'adsorption sur la terre.

Hantavirus infection and biodiversity in the Americas.

Species diversity has been proposed to decrease prevalence of disease in a wide variety of host-pathogen systems, in a phenomenon labeled the dilution effect. This phenomenon was first proposed and tested for vector-borne diseases but was later extended to directly transmitted parasite systems such as hantavirus. Though there seems to be clear evidence for the dilution effect in some hantavirus/rodent systems, the generality of this hypothesis remains debated. In the present meta-analysis, we examined the evidence supporting the dilution effect for hantavirus/rodent systems in the Americas. General linear models employed on data from 56 field studies identified the abundance of the reservoir rodent species and its relative proportion in the community as the only relevant variables explaining the prevalence of antibodies against hantavirus in the reservoir. Thus, we found no clear support for the dilution effect hypothesis for hantavirus/rodent systems in the Americas.

Aedes aegypti spreading in South America: new coldest and southernmost records

The geographic distribution of Aedes (Stegomyia) aegypti (L.) in South America has been expanding during the last decades. Herein we present two new distribution records that extend its southern limits towards localities with extremer environmental conditions than reported to date. San Antonio Oeste constitutes the southernmost finding for the continent (40º44'S), whereas Tandil is the infested locality with the coldest mean annual temperature in Argentina (14.17ºC). The projection of a previous distribution model for Ae. aegypti predicts these two cities as positive and suggests several other localities with suitable conditions for vector proliferation beyond its assumed distribution limits.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Hantavirus Pulmonary Syndrome Risk in Entre Ríos, Argentina.

Hantavirus pulmonary syndrome (HPS) is a severe emerging endemic disease of the Americas. Because hantavirus reservoirs are sylvatic rodents, HPS risk has been associated with occupational and recreational activities in natural and rural environments. The aim of this study was to analyze the risk of HPS in an endemic province of Argentina. For this, we explored the relationship between HPS cases occurring in Entre Ríos province between 2004 and 2015 and climate, vegetation, landscape, reservoir population, and rodent community characteristics by means of generalized linear models. We modeled HPS occurrence at each site, and both the incidence and number of cases grouped by department. The resulting best model of each analysis was applied in a GIS to build HPS risk maps. Risk of occurrence of HPS increased with tree cover and decreased with distance to rivers. We identified the south of Entre Ríos as the area with higher HPS risk, and therefore, where HPS prevention measures should be more urgently applied. Risk maps based on data available in the public domain are a useful tool that should be used by decision makers to concentrate surveillance and control efforts in those areas with highest HPS risk.

Evaluación de la epidemia argentina de Dengue, 2015-2016 / Evaluation of the argentine Dengue epidemic, 2015-2016

El dengue es una de las principales enfermedades tropicales emergentes. Se estima que 3.900 millones de personas, de 128 países, están en riesgo de infección por los virus del dengue. En Argentina al mosquito Aedes aegypti, vector del virus del dengue, se lo consideró erradicado en 1963 y 1965. En nuestro país el dengue reemergió en el año 1998 ocasionando desde entonces brotes de distinta magnitud cada año (excepto 2001 y 2005 donde no hubo casos registrados). Con anterioridad a la temporada 2015-2016, el brote de mayor magnitud ocurrió en 2009 con más de 26.000 casos. La mayor parte de los brotes en Argentina comenzaron en localidades limítrofes con Bolivia, Paraguay y Brasil para luego extenderse a otras localidades más alejadas. Éste trabajo pretendió estudiar la dinámica espacio-temporal de la distribución de casos de dengue de la Argentina y los factores ambientales y sociodemográficos a los que estuvieron asociados en las epidemias de 2009 y 2015-2016. En esta investigación se trabajó con técnicas de reconocimiento de variables predictivas para la ocurrencia y dispersión de los brotes de dengue en el territorio. Como era esperable, el clima y las epidemias en países limítrofes fueron cruciales para pronosticar la transmisión en el país, que continúa mostrando un comportamiento epidémico respecto al dengue. Los modelos espacio-temporales de la distribución de casos entre 2009 y 2016 mostraron también relación al mismo tipo de variables, pero priorizando la situación de circulación de virus en países limítrofes

Immature mosquitoes from groundwater habitats in a temperate wetland of Argentina: environmental associations and seasonal variation of community attributes.

We studied the seasonal patterns of 3 community attributes (breeding site index, richness, and diversity) of groundwater mosquito immatures and their associations with meso- and microhabitat factors in the Parana Lower Delta, Argentina, from December 2009 to November 2010. Monthly collections at 4 sites yielded 2,313 mosquito immatures, belonging to 19 species assigned to 6 genera. Immatures developed in a wide range of microenvironmental conditions (water temperature 4.0-30.2 degrees C, pH 5.4-9.1, electrical conductivity 0.02-6.33 mS/cm, and dissolved oxygen 0-235.6%), and their occurrence was significantly associated with lower water temperature and dissolved oxygen values. Most frequently captured species were Culex dolosus s.l. (58.6%), Aedes crinifer (22.9%), and Cx. intrincatus (19.0%). Breeding site index was highest in winter (0.76) and lowest in spring (0.54). Species richness and diversity varied significantly among seasons (peaking in summer), land uses, and habitat types.

Mosquito community structure in phytotelmata from a South American temperate wetland.

Phytotelmata, or plant-held waters, are considered to be good model systems for the study of community ecology. The fauna of these natural container habitats, particularly the mosquitoes, have been extensively investigated in tropical regions, but there is little known about them in temperate South America. We assessed the structure of immature mosquito communities in leaf axils, tree holes, and bamboo stumps from a temperate wetland of Argentina. A total of 4,330 immature mosquitoes were collected among the 2,606 phytotelmata inspected. Leaf axils of eight plant species and tree holes were larval habitats for nine mosquito species belonging to the genus Culex, Wyeomyia, Isostomyia, and Toxorhynchites. The mosquito communities showed richness ranging from one to four species. Marked differences were detected in the plant specificity for the species collected. Some of them were exclusively found in one plant species (Isostomyia paranensis in Scirpus giganteus), whereas others were collected in up to five plant species but belonging to the same phytotelm class, the leaf axils. Those from tree holes are well-known dwellers of artificial containers and ground water habitats, such as Culex pipiens. Our results support the idea of low mosquito richness in phytotelmata from temperate regions in comparison with tropical areas, but the observed specificity patterns echo the findings of tropical forests.