Geographical limits of the Southeastern distribution of Aedes aegypti (Diptera, Culicidae) in Argentina

The current geographical distribution of Aedes aegypti in South America is dramatically expanding inside Argentina, reaching a wider distribution than during its early eradication in 1967. Simultaneously, cases of dengue have increased during the last few years, and the situation has been recently worsened by the confirmation of the presence of the different dengue serotypes simultaneously circulating in new regions. Here we report on the passive south-eastern dispersion of A. aegypti in Argentina.Fil: Díaz Nieto, Leonardo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biociencias Agrícolas y Ambientales. Grupo Vinculado al Centro de Estudios de la Biodiversidad y Biotecnología de Mar del Plata- INBA. Fundación para Investigaciones Biológicas Aplicadas; ArgentinaFil: Maciá, Arnaldo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Entomología; ArgentinaFil: Perotti, M. Alejandra. University of Reading. School of Biological Sciences; Reino UnidoFil: Berón, Corina Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biociencias Agrícolas y Ambientales. Grupo Vinculado al Centro de Estudios de la Biodiversidad y Biotecnología de Mar del Plata- INBA. Fundación para Investigaciones Biológicas Aplicadas; Argentin

The Extinction of Dengue through Natural Vulnerability of Its Vectors

Dengue transmission has not always been confined to tropical areas. In some cases, this has been due to a reduced geographic range of the mosquitoes that are able to carry dengue viruses. In Australia, Aedes aegypti mosquitoes once occurred throughout temperate, drier parts of the country but are now restricted to the wet tropics. We used a computer modelling approach to determine whether these mosquitoes could inhabit their former range. This was done by simulating dengue mosquito populations in virtual environments that experienced 10 years of actual daily weather conditions (1998–2007) obtained for 13 locations inside and outside the current tropical range. We discovered that in areas outside the Australian wet tropics, Ae. aegypti often becomes extinct, particularly when conditions are too cool for year-round egg-laying activity, and/or too dry for eggs to hatch. Thus, despite being a global pest and disease vector, Ae. aegypti mosquitoes are naturally vulnerable to extinction in certain conditions. Such vulnerability should be exploited in vector control programs

Variation in Vector Competence for Dengue Viruses Does Not Depend on Mosquito Midgut Binding Affinity

Several factors, such as mosquito and virus genetics and environmental variables, determine the ability of mosquitoes to transmit dengue viruses. In this report, we describe new and important information that in some ways contradicts what is in the literature. Midgut infection barriers have been described as important determinants of virus transmission in mosquitoes but we found that virus binding to these midgut cells does not vary. When we compared binding of 8 different, low passage dengue viruses to mosquito midguts that were dissected out of Aedes aegypti mosquitoes (the main vectors of dengue) from Mexico and Texas, we found that there were no differences. Previously, we (and others) had shown that these same viruses differed significantly in replication and dissemination throughout the rest of the mosquito body, including the salivary glands, and therefore they differed greatly in their potential to be transmitted to humans. Thus, the data presented here are important considerations for future studies of vector competence and in determining strategies for control of dengue viruses in the vector

Phylogeography of Recently Emerged DENV-2 in Southern Viet Nam

Revealing the dispersal of dengue viruses (DENV) in time and space is central to understanding their epidemiology. However, the processes that shape DENV transmission patterns at the scale of local populations are not well understood, particularly the impact of such factors as human population movement and urbanization. Herein, we investigated trends in the spatial dynamics of DENV-2 transmission in the highly endemic setting of southern Viet Nam. Through a phylogeographic analysis of 168 full-length DENV-2 genome sequences obtained from hospitalized dengue cases from 10 provinces in southern Viet Nam, we reveal substantial genetic diversity in both urban and rural areas, with multiple lineages identified in individual provinces within a single season, and indicative of frequent viral migration among communities. Focusing on the recently introduced Asian I genotype, we observed particularly high rates of viral exchange between adjacent geographic areas, and between Ho Chi Minh City, the primary urban center of this region, and populations across southern Viet Nam. Within Ho Chi Minh City, patterns of DENV movement appear consistent with a gravity model of virus dispersal, with viruses traveling across a gradient of population density. Overall, our analysis suggests that Ho Chi Minh City may act as a source population for the dispersal of DENV across southern Viet Nam, and provides further evidence that urban areas of Southeast Asia play a primary role in DENV transmission. However, these data also indicate that more rural areas are also capable of maintaining virus populations and hence fueling DENV evolution over multiple seasons

Population density, water supply, and the risk of dengue fever in Vietnam: cohort study and spatial analysis.

BACKGROUND: Aedes aegypti, the major vector of dengue viruses, often breeds in water storage containers used by households without tap water supply, and occurs in high numbers even in dense urban areas. We analysed the interaction between human population density and lack of tap water as a cause of dengue fever outbreaks with the aim of identifying geographic areas at highest risk. METHODS AND FINDINGS: We conducted an individual-level cohort study in a population of 75,000 geo-referenced households in Vietnam over the course of two epidemics, on the basis of dengue hospital admissions (n = 3,013). We applied space-time scan statistics and mathematical models to confirm the findings. We identified a surprisingly narrow range of critical human population densities between around 3,000 to 7,000 people/km² prone to dengue outbreaks. In the study area, this population density was typical of villages and some peri-urban areas. Scan statistics showed that areas with a high population density or adequate water supply did not experience severe outbreaks. The risk of dengue was higher in rural than in urban areas, largely explained by lack of piped water supply, and in human population densities more often falling within the critical range. Mathematical modeling suggests that simple assumptions regarding area-level vector/host ratios may explain the occurrence of outbreaks. CONCLUSIONS: Rural areas may contribute at least as much to the dissemination of dengue fever as cities. Improving water supply and vector control in areas with a human population density critical for dengue transmission could increase the efficiency of control efforts. Please see later in the article for the Editors' Summary

Consequences of the Expanding Global Distribution of Aedes albopictus for Dengue Virus Transmission

The dramatic global expansion of Aedes albopictus in the last three decades has increased public health concern because it is a potential vector of numerous arthropod-borne viruses (arboviruses), including the most prevalent arboviral pathogen of humans, dengue virus (DENV). Ae. aegypti is considered the primary DENV vector and has repeatedly been incriminated as a driving force in dengue's worldwide emergence. What remains unresolved is the extent to which Ae. albopictus contributes to DENV transmission and whether an improved understanding of its vector status would enhance dengue surveillance and prevention. To assess the relative public health importance of Ae. albopictus for dengue, we carried out two complementary analyses. We reviewed its role in past dengue epidemics and compared its DENV vector competence with that of Ae. aegypti. Observations from “natural experiments” indicate that, despite seemingly favorable conditions, places where Ae. albopictus predominates over Ae. aegypti have never experienced a typical explosive dengue epidemic with severe cases of the disease. Results from a meta-analysis of experimental laboratory studies reveal that although Ae. albopictus is overall more susceptible to DENV midgut infection, rates of virus dissemination from the midgut to other tissues are significantly lower in Ae. albopictus than in Ae. aegypti. For both indices of vector competence, a few generations of mosquito colonization appear to result in a relative increase of Ae. albopictus susceptibility, which may have been a confounding factor in the literature. Our results lead to the conclusion that Ae. albopictus plays a relatively minor role compared to Ae. aegypti in DENV transmission, at least in part due to differences in host preferences and reduced vector competence. Recent examples of rapid arboviral adaptation to alternative mosquito vectors, however, call for cautious extrapolation of our conclusion. Vector status is a dynamic process that in the future could change in epidemiologically important ways

Higher Infection of Dengue Virus Serotype 2 in Human Monocytes of Patients with G6PD Deficiency

The prevalence of glucose-6-phosphate dehydrogenase (G6PD) deficiency is high in Asia. An ex vivo study was conducted to elucidate the association of G6PD deficiency and dengue virus (DENV) infection when many Asian countries are hyper-endemic. Human monocytes from peripheral mononuclear cells collected from 12 G6PD-deficient patients and 24 age-matched controls were infected with one of two DENV serotype 2 (DENV-2) strains–the New Guinea C strain (from a case of dengue fever) or the 16681 strain (from a case of dengue hemorrhagic fever) with a multiplicity of infection of 0.1. The infectivity of DENV-2 in human monocytes was analyzed by flow cytometry. Experimental results indicated that the monocytes of G6PD-deficient patients exhibited a greater levels of infection with DENV-2 New Guinea C strain than did those in healthy controls [mean±SD:33.6%±3.5 (27.2%∼39.2%) vs 20.3%±6.2 (8.0%∼30.4%), P<0.01]. Similar observations were made of infection with the DENV-2 16681 strain [40.9%±3.9 (35.1%∼48.9%) vs 27.4%±7.1 (12.3%∼37.1%), P<0.01]. To our knowledge, this study demonstrates for the first time higher infection of human monocytes in G6PD patients with the dengue virus, which may be important in increasing epidemiological transmission and perhaps with the potential to develop more severe cases pathogenically

Australia's Dengue Risk Driven by Human Adaptation to Climate Change

Current and projected rainfall reduction in southeast Australia has seen the installation of large numbers of government-subsidised and ad hoc domestic water storage containers that could create the possibility of the mosquito Ae. aegypti expanding out of Queensland into southern Australian's urban regions. By assessing the past and current distribution of Ae. aegypti in Australia, we construct distributional models for this dengue vector for our current climate and projected climates for 2030 and 2050. The resulting mosquito distribution maps are compared to published theoretical temperature limits for Ae. aegypti and some differences are identified. Nonetheless, synthesising our mosquito distribution maps with dengue transmission climate limits derived from historical dengue epidemics in Australia suggests that the current proliferation of domestic water storage tanks could easily result in another range expansion of Ae. aegypti along with the associated dengue risk were the virus to be introduced