Silent circulation of St. Louis encephalitis virus prior to an encephalitis outbreak in Cordoba, Argentina (2005)

Aedes (Ochlerotatus) scapularis, Aedes japonicus japonicus, and Aedes (Fredwardsius) vittatus (Diptera: Culicidae): Three Neglected Mosquitoes with Potential Global Health Risks

More than 3550 species of mosquitoes are known worldwide, and only a fraction is involved in the transmission of arboviruses. Mosquitoes in sylvatic and semi-sylvatic habitats may rapidly adapt to urban parks and metropolitan environments, increasing human contact. Many of these mosquitoes have been found naturally infected with arboviruses from the Alphaviridae, Flaviviridae, and Bunyaviridae families, with many being the cause of medically important diseases. However, there is a gap in knowledge about the vector status of newly invasive species and their potential threat to human and domestic animal populations. Due to their rapid distribution, adaptation to urban environments, and anthropophilic habits, some neglected mosquito species may deserve more attention regarding their role as secondary vectors. Taking these factors into account, we focus here on Aedes (Ochlerotatus) scapularis (Rondani), Aedes japonicus japonicus (Theobald), and Aedes (Fredwardsius) vittatus (Bigot) as species that have the potential to become important disease vectors. We further discuss the importance of these neglected mosquitoes and how factors such as urbanization, climate change, and globalization profoundly alter the dynamics of disease transmission and may increase the participation of neglected species in propagating diseases.

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 meal sources of mosquitoes (Diptera: Culicidae) in domestic and open green environments from two urbanisations of temperate Argentina

Understanding the blood-feeding patterns of mosquitoes is essential for evaluating their potential as disease vectors, especially in urban areas where mosquitoes coexist with humans, domestic animals and wildlife. This study aimed to bridge a substantial gap in regional knowledge by identifying the blood meal sources of field-collected mosquitoes in domestic and open green environments from two urbanisations of temperate Argentina, the Área Metropolitana de Buenos Aires (AMBA) and Tandil, using molecular techniques. Female mosquitoes were collected from November 2019 to March 2020 and April-May 2021. A bipartite network analysis was performed for each environment and urbanisation. A total of 103 blood meals from Aedes (2 species) and Culex (7 species) were identified. Among these, five mammal and 18 bird species were recognised as hosts. Aedes mosquitoes exclusively fed on mammals, while Culex mosquitoes exhibited a broader host range including both birds and mammals. In AMBA, the open green environments were composed by more mosquito species than the domestic environments, while both presented similar numbers of vertebrate species. In contrast, in open green environments from Tandil only blood-fed Aedes albifasciatus were collected. For open green environments of AMBA and domestic environments of Tandil, results suggested some degree of host selection. For the three main vectors of diseases in the region, Aedes aegypti, Ae. albifasciatus and Culex pipiens molestus, we present the first molecular evidence of human blood meals in South America. Epidemiological significance of the present findings is discussed.

Host-mosquito interactions in rural and urban equestrian facilities from temperate Argentina

Targeted vector surveillance informed by data on mosquito biting patterns can help limit arboviral zoonotic diseases. To characterise host-biting networks in rural and urban equestrian facilities from temperate Argentina, adult resting mosquitoes were collected (December 2018-April 2019) with a battery-powered aspirator. Engorged females were sorted to species, and their blood source was identified using molecular techniques. Bipartite network analysis was performed for rural and urban matrices. A total of 177 bloodmeals from 11 mosquito species of Aedes and Culex were identified, with seven mammal and 17 bird species recognised as hosts. Mammals represented 61% of the total feeds, mainly horse, dog and sheep; the best represented avian hosts were Columbiformes. Aedes species and Culex maxi fed only on mammals, while most other Culex species presented a wide range of hosts. The rural network had more nodes and interactions than its urban counterpart, both with some degree of host selection and aggregated patterns according to network indices. Culex quinquefasciatus was the strongest species in both networks, whereas Culex apicinus and Culex dolosus had a prominent role in the rural network. Bipartite network analysis will contribute to understanding the effects of urbanisation in the dynamics of vector-borne diseases.

Prevalence of Mosquito Populations in the Caribbean Region of Colombia with Important Public Health Implications

Mosquito studies are important for understanding their role in the transmission of pathogens including arboviruses, parasites, and protozoa. This study characterized the prevalence of Culicidae fauna in rural and peri-urban areas with human populations in the Colombian Caribbean region to establish the risk of transmission of mosquito-borne pathogens. From 2016 to 2017, adult mosquitos were collected in Turbaco (Bolívar), Sabanalarga (Atlántico) and Pueblo Bello (Cesar). The collections in rural areas were in the forest fragments using CDC, Shannon, and human bait traps. In peri-urban areas, Prokopack aspirator collections were used inside households. Entomological and ecological indicators were also calculated. A total of 11,566 mosquito specimens, from 13 genera and 63 species, were collected. The forests fragments of Sabanalarga and Turbaco had the highest species abundance and richness. Turbaco had the highest adult Aedes aegypti index. Arbovirus vectors were among the identified species, including Ae. aegypti, Culex quinquefasciatus, Haemagogus janthinomys, Sabethes chloropterus, Aedes angustivittatus, Mansonia titillans, Coquillettidia venezuelensis and the subgenera Culex Melanoconion. Overall, the diversity and abundance of mosquitoes present in these municipalities establish a potential disease transmission risk by these vectors.

Blood feeding habits of mosquitoes: hardly a bite in South America

Mosquito blood feeding plays a key role in epidemiology. Despite its importance and large number of studies worldwide, less attention has been paid in South America. We summarized some general concepts and methodological issues related to the study of mosquito blood feeding habits, and compiled and analyzed all published information regarding the subject in the continent until 2020. Available literature comprised 152 scientific studies, that pursued different approaches: human landing catches (102 studies), baited trap (19), and blood meal analyses of collected specimens (38). Among the latter, 23 used serological and 15 molecular techniques. Species most frequently studied were those incriminated in malaria transmission, whereas relevant vectors such as Aedes aegypti, Ae. albopictus, and Haemagogus janthinomys were surprisingly neglected. Brazil was the leading country both in number of works and species studied. For over 70% of the species and three out of 13 South American countries there is no single information on mosquito blood feeding habits. Data from baited traps included 143 mosquito species, 83.9% of which were attracted to humans, either exclusively (10.5%) or in combination with other vertebrates (73.4%). Host blood identification of field collected specimens provided data on 102 mosquito species, and 60.8% of these fed on humans (55.9% combined with other vertebrates). Only 17 of the 73 species assessed by both methods yielded similar feeding patterns. Finally, supplementary tables are provided in a comprehensive summary of all information available and information gaps are highlighted for future research in the continent.

Ecological Characterization of Mosquitoes (Diptera: Culicidae) at the Southern Coast of Mar Chiquita Lake, Argentina

In the southern coast of Mar Chiquita Lake, central Argentina, mosquitoes affect public health and community livelihood, since they transmit pathogens to human beings causing diseases such as malaria, filariasis, encephalitis, yellow fever, and dengue, among others, and have a negative effect on cattle farming as well. To characterize the structure of the mosquito assemblage of the region, we determined the species composition and diversity, the temporal distribution of different species, and the patterns of species richness, abundance, and diversity across seasons. We collected adult mosquitoes over a two-year period (October 2004-September 2006) by means of CDC light traps baited with CO2 from 18:00 to 08:00 h during the warm season (October-April) and from 12:00 h to 18:00 h in the cold season (May-September). A total of 71,501 individuals from 30 species were collected, with Culex Linnaeus and Aedes Meigen genera representing more than 98% of collected specimens (61.5% and 37.3%, respectively). The higher values of richness and abundance of Culicidae were registered in warm seasons compared to cold seasons. Chao1 estimates suggested that more than 90% of the species were detected in all seasons. Mosquito abundance distribution fit the logarithmic series and log-normal models. Aedes albifasciatus (Macquart), Ae. scapularis (Rondani), Culex interfor Dyar, Cx. saltanensis Dyar, and Cx. dolosus (Lynch Arribálzaga), vectors incriminated in arbovirus transmission, were abundant year-round, with Cx. saltanensis and Cx. dolosus most prevalent in cold seasons. Further studies are needed to assess the role of these species in arbovirus transmission in this region of central Argentina.

The RNA Secondary Structure Analysis Reveals Potential for Emergence of Pathogenic Flaviviruses

The Flavivirus genus is divided into four groups: Mosquito-borne flaviviruses, Tick-borne flaviviruses, no-known vector flaviviruses, and Insect specific flaviviruses. Millions of people are affected worldwide every year due to the flaviviral infections. The 5' UTR of the RNA genome plays a critical role in the biology of flaviviruses. To explore any correlation between the topology of the 5' UTR and pathogenesis, a global scale study of the RNA secondary structure of different groups of flaviviruses has been conducted. We found that most of the pathogenic flaviviruses, irrespective of their mode of transmission, tend to form a Y shaped topology in the Stem loop A of the 5' UTR. Some of the current non-pathogenic flaviviruses were also observed to form Y shaped structure. Based on this study, it has been proposed that the flaviviruses having the Y shaped topology in their 5' UTR regions may have the potential to become pathogenic.

Behavior of Aedes albifasciatus (Diptera: Culicidae) larvae from eggs with different dormancy times and its relationship with parasitism by Strelkovimermis spiculatus (Nematoda: Mermithidae)

Aedine mosquitoes go through unfavorable periods as dormant eggs. However, extended dormancy times lead to a depletion of egg reserves, which might be partially compensated by changes in larval-feeding behavior. Changes in larval behavior may also be induced by parasitism by mermithids probably as a strategy to reduce the impact of the parasite on the host. The most abundant floodwater mosquito in southern South America is Aedes albifasciatus (Diptera: Culicidae), a species naturally parasitized by Strelkovimermis spiculatus (Nematoda: Mermithidae). This study aimed to evaluate the behavior of fourth-instar larvae of Ae. albifasciatus from eggs with 2, 4, and 6 months of dormancy, parasitized or not by S. spiculatus. To achieve this, eight categories of behavior were defined, and then, each individual was observed for 5 min, and its behaviors and their duration were recorded. The behaviors with the highest percentage of observation time were still (50.1%) and wriggle swimming (33.6%), while those with the lowest percentage of observation time were those involving active foraging (less than 8%). A great variability in the behaviors was observed among individuals within the same treatment. The type and duration of each behavior did not vary in relation to egg dormancy time or parasitism, but parasitism affected the level of larval activity. Parasitized larvae performed, on average, fewer behaviors than non-parasitized larvae. This result supports the hypothesis that S. spiculatus parasitism affects the behavior of Ae. albifasciatus larvae by reducing their level of activity.

West Nile Virus in the State of Ceará, Northeast Brazil

In June 2019, a horse with neurological disorder was diagnosed with West Nile virus (WNV) in Boa Viagem, a municipality in the state of Ceará, northeast Brazil. A multi-institutional task force coordinated by the Brazilian Ministry of Health was deployed to the area for case investigation. A total of 513 biological samples from 78 humans, 157 domestic animals and 278 free-ranging wild birds, as well as 853 adult mosquitoes of 22 species were tested for WNV by highly specific serological and/or molecular tests. No active circulation of WNV was detected in vertebrates or mosquitoes by molecular methods. Previous exposure to WNV was confirmed by seroconversion in domestic birds and by the detection of specific neutralizing antibodies in 44% (11/25) of equids, 20.9% (14/67) of domestic birds, 4.7% (13/278) of free-ranging wild birds, 2.6% (2/78) of humans, and 1.5% (1/65) of small ruminants. Results indicate that not only equines but also humans and different species of domestic animals and wild birds were locally exposed to WNV. The detection of neutralizing antibodies for WNV in free-ranging individuals of abundant passerine species suggests that birds commonly found in the region may have been involved as amplifying hosts in local transmission cycles of WNV.

Gonoactivity of Culex (Culex) (Diptera: Culicidae) Mosquitoes During Winter in Temperate Argentina

The subgenus Culex L. includes species involved in summer-autumn arbovirus transmission but studies during winter are scarce in temperate Argentina. Female specimens were collected host-seeking at dry-ice-baited traps during autumn-winter-spring at two sites in Córdoba City during 2016 and 2017. The specimens were morphologically identified and dissected to determine the follicular developmental stage (gonotrophic activity). Females with advanced follicular stages (≥III) were subjected to molecular procedures to confirm or re-identify previous morphological identification. Five species (Culex apicinus Philippi (Diptera: Culicidae), Culex dolosus (Lynch-Arribálzaga) (Diptera: Culicidae), Culex maxi Dyar (Diptera: Culicidae), Culex pipiens pipiens L. (Diptera: Culicidae), and Culex quinquefasciatus Say (Diptera: Culicidae)) were collected and found gonoactive during winter; showing that a high proportion of Culex (Culex) females remain reproductively active during the unfavorable season for mosquito populations. Among them, it is worth noting the collection of Cx. quinquefasciatus, vector of the St. Louis encephalitis virus (endemic in the city), a specimen of Cx. p. pipiens, and a hybrid of Cx. p. pipiens/Cx. quinquefasciatus (during autumn). The study of this community during winter should continue because a high gonoactive female proportion with advanced follicular stages was found: 29.12 and 13.07% in 2016 and 2017, respectively. Local studies such as this one provide evidence about ornithophilic Culex species with active year-round life cycles, species that could favor arbovirus overwintering.

Is There a Minimum Number of Landmarks That Optimizes the Geometric Morphometric Analysis of Mosquito (Diptera, Culicidae) Wings?

Culicids are the most significant arthropods affecting human health. Thus, their correct identification is critical. The use of Geometric Morphometrics (GM) has been recently incorporated into mosquito taxonomy and has begun to complement classic diagnostic techniques. Since sampling size depends on the number of Landmarks (LMs) used, this study aimed to establish the minimum number of wing LMs needed to optimize GM analysis of mosquito species and/or genera from urban and peri-urban areas of Argentina. Female left wings were used for the optimization phase, in which 17 LMs were reduced to four by iterative LM exclusion. To verify its efficiency, Principal Component Analysis (PCA), Discriminant Analysis (DA), and Canonical Variate Analysis (CVA) were performed. Additionally, a phenogram was constructed to visualize the results. We observed that five LMs for the PCA, CVA, and phenogram and nine for the DA enabled discrimination and/or clustering of almost all species and genera. Therefore, we tested the LM selection by using nine LMs and adding new species. The resulting PCA showed little overlap between species and almost all species clustered as expected, which was also reflected in the phenogram. Significant differences were found between wing shape among all species, together with a low total error rate in the DA. In conclusion, the number of LMs can be reduced and still be used to effectively differentiate and cluster culicids. This is helpful for better exploitation of available material and optimization of data processing time when classic taxonomy methods are inadequate or the material is scarce.

Susceptibility of the floodwater mosquito Aedes albifasciatus from eggs of different dormancy times to the nematode parasite Strelkovimermis spiculatus

This study aimed to evaluate the effects of egg dormancy times on susceptibility of larvae of the floodwater mosquito Aedes albifasciatus (Diptera: Culicidae) to parasitism by their natural enemy Strelkovimermis spiculatus (Nematoda: Mermithidae) and on their life history traits. Aedes albifasciatus eggs stored for 2, 4, 6, 8 and 10 months were hatched, and the larvae either exposed to S. spiculatus (treatment group) or not exposed (control group). Egg dormancy time had a negative effect on the retention of parasites, but no effect on the prevalence and intensity of parasitism or the melanization of nematodes. The survival to adulthood of control individuals decreased as dormancy time increased, whereas that of exposed individuals that remained uninfected was constant and low. A trend towards increasing development times with longer dormancy times was detected in the control group, but not in the exposed noninfected group. The results suggest nonconsumptive effects of parasites in exposed but not infected larvae from eggs with short dormancy times. In contrast, the relatively low fitness of larvae from eggs with long dormancy times regardless of their contact with the nematodes may be the result of the nutritional deprivation during the egg stage.

Zoonotic Diseases from Horses: A Systematic Review

Background: Worldwide, horses play critical roles in recreation, food production, transportation, and as working animals. Horses' roles differ by geographical region and the socioeconomic status of the people, but despite modern advances in transportation, which have in some ways altered humans contact with horses, potential risks for equine zoonotic pathogen transmission to humans occur globally. While previous reports have focused upon individual or groups of equine pathogens, to our knowledge, a systematic review of equine zoonoses has never been performed. Methods: Using PRISMA's systematic review guidelines, we searched the English literature and identified 233 previous reports of potential equine zoonoses found in horses. We studied and summarized their findings with a goal of identifying risk factors that favor disease transmission from horses to humans. Results: These previous reports identified 56 zoonotic pathogens that have been found in horses. Of the 233 articles, 13 involved direct transmission to humans (5.6%).The main potential routes of transmission included oral, inhalation, and cutaneous exposures. Pathogens most often manifest in humans through systemic, gastrointestinal, and dermatological signs and symptoms. Furthermore, 16.1% were classified as emerging infectious diseases and thus may be less known to both the equine and human medical community. Sometimes, these infections were severe leading to human and equine death. Conclusions: While case reports of zoonotic infections directly from horses remain low, there is a high potential for underreporting due to lack of knowledge among health professionals. Awareness of these zoonotic pathogens, their disease presentation in horses and humans, and their associated risk factors for cross-species infection are important to public health officials, clinicians, and people with recreational or occupational equid exposure.

Mosquito Iridescent Virus: New Records from Nature and Infections Using Strelkovimermis spiculatus (Mermithidae) as a Vector Under Laboratory Conditions

Iridoviridae is a DNA virus family that affects both vertebrates and invertebrates. Immature aquatic stages of many dipteran species infected with iridovirus have been found in different places worldwide. The most represented genera of the Culicidae family are Aedes and Psorophora. To date, sixteen species of Aedes naturally infected with iridoviruses have been reported. Moreover, there are four records for the genus Psorophora, one for Culiseta, and two for Culex. In this paper, we report two new mosquito species as natural hosts of iridoviridae in Argentina: Aedes albifasciatus (Macquart) and Culex dolosus (Lynch Arribalzaga). We also analyzed the ability of a Cx. pipiens-Invertebrate Iridescent Virus to replicate in vivo in the larval stage of two mosquito species, Culex apicinus Philippi and Ae. aegypti (L.) using Strelkovimermis spiculatus as a vector, under laboratory conditions. Although Ae. aegypti is the most recognized mosquito vector of important arboviruses responsible for emergent diseases, Cx. apicinus and Ae. albifasciatus may also be implicated in enzootic or epizootic cycles of virus transmission, such as the St. Louis Encephalitis virus and the Western Equine Encephalomyelitis virus.

Silent Circulation of the Saint Louis Encephalitis Virus among Humans and Equids, Southeast Brazil

Saint Louis encephalitis virus (SLEV) is a mosquito-borne flavivirus that occurs throughout the Americas, and is considered a public health threat. In Brazil, SLEV has been detected from human cases associated with dengue-like disease, but no neurological symptoms were reported. Furthermore, the epidemiology of SLEV in human populations is still poorly explored in the country. We reported serological and molecular detection of SLEV in a healthy population of equids and humans from rural areas in Southeast Brazil. A plaque reduction neutralization test was applied, and neutralizing antibodies were detected in 11 individuals (4.6%) and 60 horses (21.5%). A qPCR targeting the 5′UTR region and reverse transcription-PCR (RT-PCR) targeting the non-structural protein (NS5) gene were performed and three individuals tested positive in both assays. Subsequent phylogenetic analysis confirmed SLEV circulation and its findings suggest the occurrence of an asymptomatic or subclinical presence in human and animal cases, correlating with the risks for outbreaks and consequently burden of SLEV infections to public health. Preventive strategies should include improved surveillance in regions with a high probability of SLEV occurrence, improvement in diagnostic methods, and evaluation of exposure/risk factors that can favor SLEV emergence.

Reemergence of St. Louis Encephalitis Virus in the Americas

In the western United States, this virus may have been mediated via migrating infected birds from southern South America, where it reemerged most recently in 2002.

We summarize and analyze historical and current data regarding the reemergence of St. Louis encephalitis virus (SLEV; genus Flavivirus) in the Americas. Historically, SLEV caused encephalitis outbreaks in the United States; however, it was not considered a public health concern in the rest of the Americas. After the introduction of West Nile virus in 1999, activity of SLEV decreased considerably in the United States. During 2014–2015, SLEV caused a human outbreak in Arizona and caused isolated human cases in California in 2016 and 2017. Phylogenetic analyses indicate that the emerging SLEV in the western United States is related to the epidemic strains isolated during a human encephalitis outbreak in Córdoba, Argentina, in 2005. Ecoepidemiologic studies suggest that the emergence of SLEV in Argentina was caused by the introduction of a more pathogenic strain and increasing populations of the eared dove (amplifying host).

Mosquito (Diptera: Culicidae) larval ecology in natural habitats in the cold temperate Patagonia region of Argentina

BACKGROUND

Knowledge of immature habitats is an important focus for investigations of mosquito community ecology, and may improve our understanding of how environmental variables increase risk of mosquito-borne diseases by influencing the distributions and abundances of species. In Patagonia region, where climatic and ecological factors could be only borderline suitable for mosquito development, relatively little is known about larval ecology. The present study focuses on associations of environmental conditions in natural aquatic habitats with abundances of mosquito species that have colonized such habitats in Patagonia.

METHODS

We described the mosquito community composition within 26 natural temporary pools, and assessed the general relationships between environmental variables (pH, water temperature, conductivity, salinity, dissolved oxygen, aquatic plant cover and main nutrients) and larval abundances using redundancy analysis (RDA). Additionally, we compiled monthly climate data and vegetation indices for each larval habitat, and estimated the probability of presence for two of the most abundant species, describing through generalized linear models (GLM) the environmental, climatic and landscape variables-probability of occurrence relationships.

RESULTS

Seven species belonging to the genera Culex and Aedes were identified, with Culex apicinus, Cx. acharistus and Aedes albifasciatus being the most abundant. Mean larval densities were low (6.8 ± 2.8 larvae/dip), and the highest species richness and larval densities were recorded in northern and central areas. Aedes albifasciatus, a species of sanitary importance, was widely distributed, being the only one collected south of the 45th parallel of S latitude. RDA indicated that aquatic conductivity, pH, water depth, dissolved oxygen, ammonia and soluble reactive phosphorous accounted for the main part of the variation in the species composition. According to GLMs, wind speed was the variable that best described the presence of Ae. albifasciatus, and the probability of finding this species was positively associated with high wind speed values. On the other hand, the EVI vegetation index was the only variable included in the Cx. apicinus model, whereby there was a great probability of presence in arid areas with lower EVI values.

CONCLUSIONS

Our results enhance our knowledge of larval habitat ecology under the extreme environmental conditions of Patagonia and will guide future efforts to understand how multiple effects can affect mosquito ecology and public health at higher latitudes.

Wing morphometrics of Aedes (Ochlerotatus) albifasciatus (Macquart, 1838) (Diptera: Culicidae) from different climatic regions of Argentina

BACKGROUND

Gene flow restrictions between populations of Aedes albifasciatus, the vector of Western equine encephalitis and Dirophilaria immitis, have been described in the central region of Argentina. Genetic and eco-physiological variations usually result in local forms reflecting the climatic regions. Mosquito wings and their different parts have ecological functions in flight and communication. Therefore, wing shape could be considered an aspect of sexual dimorphism, and its eco-physiological responses can be expressed as morphological changes induced by the environment.

METHODS

To compare the geographical and sexual variations with respect to wing shape and size in two Ae. albifasciatus populations from contrasting climates of Argentina (temperate: Buenos Aires, and the arid steppe of Patagonia: Sarmiento), the wings of adults reared in thermal trays at different constant temperatures (10-29 °C) were analyzed.

RESULTS

The wing size of Ae. albifasciatus showed inverse linear relationships with the rearing thermal condition and higher slope for Buenos Aires. In the cool range (10-17 °C), geographical size variations responded to the converse Bergmann's rule, where Buenos Aires individuals were larger than those from Sarmiento. Sexual shape dimorphism occurred in both populations while geographical variation in shape was observed in both sexes.

CONCLUSIONS

Buenos Aires individuals showed greater response sensitivity with respect to the size-temperature relation than those from Sarmiento. The converse Bergmann's rule in size variation could be due to a higher development rate in Sarmiento to produce more cohorts in the limited favorable season. The shape could be more relevant with respect to the size in the study of population structures due to the size being more liable to vary due to changes in the environment. The geographical variations with respect to morphology could be favored by the isolation between populations and adaptations to the environmental conditions. Our results demonstrate that the shape and size of wing provide useful phenotypic information for studies related to sexual and environmental adaptations.

Evaluation of Argentinean Bird Species as Amplifying Hosts for St. Louis Encephalitis Virus (Flavivirus, Flaviviridae)

St.Louis encephalitis virus (SLEV) is an emerging human pathogen flavivirus in Argentina. Recently, it has reemerged in the United States. We evaluated the role as amplifying host of six resident bird species and analyzed their capacity as host during the 2005 encephalitis outbreak of SLEV in Córdoba. Eared Dove, Picui Ground Dove, and House Sparrow were the three species with highest host competence index. At a city level, Eared Dove and Picui Ground Dove were the most important amplifying hosts during the 2005 SLEV human outbreak in Córdoba city. This finding highlighted important differences in the SLEV ecology between Argentina and the United States. Characterizing and evaluating the SLEV hosts contribute to our knowledge about its ecology and could help us to understand the causes that promote its emergence as a human pathogen in South America.

Development of a model of Saint Louis encephalitis infection and disease in mice

BACKGROUND

Flaviviruses are a genre of closely related viral pathogens which emerged in the last decades in Brazil and in the world. Saint (St.) Louis encephalitis virus (SLEV) is a neglected flavivirus that can cause a severe neurological disease that may lead to death or sequelae. St. Louis encephalitis pathogenesis is poorly understood, which hinders the development of specific treatment or vaccine.

METHODS

To address this problem, we developed a model of SLEV infection in mice to study mechanisms involved in the pathogenesis of severe disease. The model consists in the intracranial inoculation of the SLEV strain BeH 355964, a strain isolated from a symptomatic human patient in Brazil, in adult immunocompetent mice.

RESULTS

Inoculated mice presented SLEV replication in the brain, accompanied by tissue damage, disease signs, and mortality approximately 7 days post infection. Infection was characterized by the production of proinflammatory cytokines and interferons and by leukocyte recruitment to the brain, composed mainly by neutrophils and lymphocytes. In vitro experiments indicated that SLEV is able to replicate in both neurons and glia and caused neuronal death and cytokine production, respectively.

CONCLUSIONS

Altogether, intracranial SLEV infection leads to meningoencephalitis in mice, recapitulating several aspects of St. Louis encephalitis in humans. Our study indicates that the central nervous system (CNS) inflammation is a major component of SLEV-induced disease. This model may be useful to identify mechanisms of disease pathogenesis or resistance to SLEV infection.

Detection of the mosquito-borne flaviviruses, West Nile, Dengue, Saint Louis Encephalitis, Ilheus, Bussuquara, and Yellow Fever in free-ranging black howlers (Alouatta caraya) of Northeastern Argentina

Several medically important mosquito-borne flaviviruses have been detected in Argentina in recent years: Dengue (DENV), St. Louis encephalitis (SLEV), West Nile (WNV) and Yellow Fever (YFV) viruses. Evidence of Bussuquara virus (BSQV) and Ilheus virus (ILHV) activity were found, but they have not been associated with human disease. Non-human primates can act as important hosts in the natural cycle of flaviviruses and serological studies can lead to improved understanding of virus circulation dynamics and host susceptibility. From July-August 2010, we conducted serological and molecular surveys in free-ranging black howlers (Alouatta caraya) captured in northeastern Argentina. We used 90% plaque-reduction neutralization tests (PRNT90) to analyze 108 serum samples for antibodies to WNV, SLEV, YFV, DENV (serotypes 1and 3), ILHV, and BSQV. Virus genome detection was performed using generic reverse transcription (RT)-nested PCR to identify flaviviruses in 51 antibody-negative animals. Seventy animals had antibodies for one or more flaviviruses for a total antibody prevalence of 64.8% (70/108). Monotypic (13/70, 19%) and heterotypic (27/70, 39%) patterns were differentiated. Specific neutralizing antibodies against WNV, SLEV, DENV-1, DENV-3, ILHV, and BSQV were found. Unexpectedly, the highest flavivirus antibody prevalence detected was to WNV with 9 (8.33%) monotypic responses. All samples tested by (RT)-nested PCR were negative for viral genome. This is the first detection of WNV-specific antibodies in black howlers from Argentina and the first report in free-ranging non-human primates from Latin-American countries. Given that no animals had specific neutralizing antibodies to YFV, our results suggest that the study population remains susceptible to YFV. Monitoring of these agents should be strengthened to detect the establishment of sylvatic cycles of flaviviruses in America and evaluate risks to wildlife and human health.

Virulence variation among epidemic and non-epidemic strains of Saint Louis encephalitis virus circulating in Argentina

Saint Louis encephalitis virus caused an outbreak of febrile illness and encephalitis cases in Córdoba, Argentina, in 2005. During this outbreak, the strain CbaAr-4005 was isolated from Culex quinquefasciatus mosquitoes. We hypothesised that this epidemic variant would be more virulent in a mouse model than two other non-epidemic strains (78V-6507 and CorAn-9275) isolated under different epidemiological conditions. To test this hypothesis, we performed a biological characterisation in a murine model, including mortality, morbidity and infection percentages and lethal infection indices using the three strains. Mice were separated into age groups (7, 10 and 21-day-old mice) and analysed after infection. The strain CbaAr-4005 was the most infective and lethal of the three variants, whereas the other two strains exhibited a decreasing mortality percentage with increasing animal age. The strain CbaAr-4005 produced the highest morbidity percentages and no significant differences among age groups were observed. The epidemic strain caused signs of illness in all inoculated animals and showed narrower ranges from the onset of symptoms than the other strains. CbaAr-4005 was the most virulent for Swiss albino mice. Our results highlight the importance of performing biological characterisations of arbovirus strains likely to be responsible for emerging or reemerging human diseases.

[Serological evidence of St. Louis encephalitis virus circulation in birds from Buenos Aires City, Argentina]

Our goal was to determine the presence of neutralizing antibodies against St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) in sera of wild and domestic birds from Buenos Aires City, Argentina. From October 2012 to April 2013, 180 samples were collected and processed by the microneutralization technique. A 7.2% of the sampled birds were seropositive for SLEV, while no seropositive birds for WNV were detected.

Exploring Genomic, Geographic and Virulence Interactions among Epidemic and Non-Epidemic St. Louis Encephalitis Virus (Flavivirus) Strains

St. Louis encephalitis virus (SLEV) is a re-emerging arbovirus in South America. In 2005, an encephalitis outbreak caused by SLEV was reported in Argentina. The reason for the outbreak remains unknown, but may have been related to virological factors, changes in vectors populations, avian amplifying hosts, and/or environmental conditions. The main goal of this study was to characterize the complete genome of epidemic and non-epidemic SLEV strains from Argentina. Seventeen amino acid changes were detected; ten were non-conservative and located in proteins E, NS1, NS3 and NS5. Phylogenetic analysis showed two major clades based on geography: the North America and northern Central America (NAnCA) clade and the South America and southern Central America (SAsCA) clade. Interestingly, the presence of SAsCA genotype V SLEV strains in the NAnCA clade was reported in California, Florida and Texas, overlapping with known bird migration flyways. This work represents the first step in understanding the molecular mechanisms underlying virulence and biological variation among SLEV strains.

St. Louis Encephalitis virus mosquito vectors dynamics in three different environments in relation to remotely sensed environmental conditions

In Argentina the St. Louis Encephalitis virus (SLEV) is an endemic and widely distributed pathogen transmitted by the cosmopolitan mosquito Culex quinquefasciatus. During two outbreaks in Córdoba city, in 2005 and 2010, Culex interfor was also found infected, but its role as vector of SLEV is poorly known. This mosquito species is distributed from central Argentina to southern Brazil. The primary aim of this study was to analyze the population dynamic of Cx. interfor and Cx. quinquefasciatus in three different environments (urban, suburban and non-urban) in relation to remotely sensed environmental data for vegetation (NDVI and NDWI) and temperature (brightness temperature). Cx. quinquefasciatus and Cx. interfor were found at the three sampled sites, being both the most abundant Culex species, with peaks in early and midsummer. Temporal distribution patterns of both mosquito species were highly correlated in a non-urban area of high SLEV risk transmission. Cx. quinquefasciatus and Cx. interfor were associated with the most urbanized site and the non-urban environment, respectively; high significant correlations were detected between vegetation indices and abundance of both mosquito species confirming these associations. These data provide a foundation for building density maps of these two SLEV mosquito vectors using remotely sensed data to help inform vector control programs.

Consequences of in vitro host shift for St. Louis encephalitis virus

Understanding the potential for host range shifts and expansions of RNA viruses is critical to predicting the evolutionary and epidemiological paths of these pathogens. As arthropod-borne viruses (arboviruses) experience frequent spillover from their amplification cycles and are generalists by nature, they are likely to experience a relatively high frequency of success in a range of host environments. Despite this, the potential for host expansion, the genetic correlates of adaptation to novel environments and the costs of such adaptations in originally competent hosts are still not characterized fully for arboviruses. In the studies presented here, we utilized experimental evolution of St. Louis encephalitis virus (SLEV; family Flaviviridae, genus Flavivirus) in vitro in the Dermacentor andersoni line of tick cells to model adaptation to a novel invertebrate host. Our results demonstrated that levels of adaptation and costs in alternate hosts are highly variable among lineages, but also that significant fitness increases in tick cells are achievable with only modest change in consensus genetic sequence. In addition, although accumulation of diversity may at times buffer against phenotypic costs within the SLEV swarm, an increased proportion of variants with an impaired capacity to infect and spread on vertebrate cell culture accumulated with tick cell passage. Isolation and characterization of a subset of these variants implicates the NS3 gene as an important host range determinant for SLEV.

Isolation of saint louis encephalitis virus from a horse with neurological disease in Brazil

St. Louis encephalitis virus (SLEV) is a causative agent of encephalitis in humans in the Western hemisphere. SLEV is a positive-sense RNA virus that belongs to the Flavivirus genus, which includes West Nile encephalitis virus, Japanese encephalitis virus, Dengue virus and other medically important viruses. Recently, we isolated a SLEV strain from the brain of a horse with neurological signs in the countryside of Minas Gerais, Brazil. The SLEV isolation was confirmed by reverse-transcription RT-PCR and sequencing of the E protein gene. Virus identity was also confirmed by indirect immunofluorescence using commercial antibodies against SLEV. To characterize this newly isolated strain in vivo, serial passages in newborn mice were performed and led to hemorrhagic manifestations associated with recruitment of inflammatory cells into the central nervous system of newborns. In summary this is the first isolation of SLEV from a horse with neurological signs in Brazil.

St. Louis encephalitis virus (SLEV), a member of the Flavivirus genus, which includes West Nile encephalitis virus, Japanese encephalitis virus, Dengue virus, and other medically important viruses, is a cause of encephalitis in humans and animals. SLEV is considered endemic in the Americas, and currently there is no vaccine or specific treatment available for controlling of preventing SLEV-induced encephalitis. In this study we describe the first isolation of SLEV from an adult male horse with neurologic disease, which was further characterized by molecular and serological methods. Phylogenetic analysis of a 903 base pairs amplified sequence from partial Envelope (E) gene region indicated that the isolate from the horse was within the cluster of the VB genotype. In addition, inoculation of the SLEV isolate intracranially in newborn mice resulted in circulatory and neurological changes. This is the first report of isolation of SLEV from a horse with neurological disease in Brazil.

Molecular phylogenetic and positive selection analysis of Japanese encephalitis virus strains isolated from pigs in China

Japanese encephalitis virus (JEV) is one of the most important virus which causes encephalitis. This disease is most prevalent in the south, southeast and the east region of Asia. In this study, two JEV strains, named JEV/SW/GD/01/2009 and JEV/SW/GZ/09/2004, were isolated from aborted fetuses and seminal fluid of pigs in China. To determine the characteristic of these virus isolates, the virulence of two newly JEV isolates was investigated, the result evidenced that the JEV/SW/GD/01/2009 did not kill mice, while the JEV/SW/GZ/09/2004 displayed neurovirulence with 0.925log10 p.f.u./LD50. Additionally, the full genome sequences of JEV were determined and compared with other known JEV strains. Results demonstrated that the genome of two JEV isolates was 10,976 nucleotides (nt) in length. As compared to the Chinese vaccine strain SA14-14-2, the JEV/SW/GD/01/2009 and the JEV/SW/GZ/09/2004 showed 99.7% and 97.5% identity at the nucleotide level, 99.6% and 96.7% identity at the amino acid level, respectively. Phylogenetic analysis, based on the full-length genome revealed that two JEV isolates were all clustered into genotype III compared to the reference strains. Furthermore, selection analyses revealed that dominant selective pressure acting on the JEV genome was purifying selection. Four sites under positive selection were identified: codon 521 (amino acid E-227), 2296 (amino acid NS4b-24), 3048 (amino acid NS5-521) and 3055 (amino acid NS5-528). Amino acid E-227 was proved to be related to neurovirulence. Taken together, the molecular epidemiology and functional of positively selected amino acid sites of two newly JEV isolates were fully understood, which might be helpful to predict possible changes in virulence.

Provenance and geographic spread of St. Louis encephalitis virus

St. Louis encephalitis virus (SLEV) is the prototypic mosquito-borne flavivirus in the Americas. Birds are its primary vertebrate hosts, but amplification in certain mammals has also been suggested. The place and time of SLEV emergence remain unknown. In an ecological investigation in a tropical rainforest in Palenque National Park, Mexico, we discovered an ancestral variant of SLEV in Culex nigripalpus mosquitoes. Those SLEV-Palenque strains form a highly distinct phylogenetic clade within the SLEV species. Cell culture studies of SLEV-Palenque versus epidemic SLEV (MSI-7) revealed no growth differences in insect cells but a clear inability of SLEV-Palenque to replicate in cells from birds, cotton rats, and free-tailed bats permissive for MSI-7 replication. Only cells from nonhuman primates and neotropical fruit bats were moderately permissive. Phylogeographic reconstruction identified the common ancestor of all epidemic SLEV strains to have existed in an area between southern Mexico and Panama ca. 330 years ago. Expansion of the epidemic lineage occurred in two waves, the first representing emergence near the area of origin and the second involving almost parallel appearances of the virus in the lower Mississippi and Amazon delta regions. Early diversification events overlapped human habitat invasion during the post-Columbian era. Several documented SLEV outbreaks, such as the 1964 Houston epidemic or the 1990 Tampa epidemic, were predated by the arrival of novel strains between 1 and 4 years before the outbreaks. Collectively, our data provide insight into the putative origins of SLEV, suggesting that virus emergence was driven by human invasion of primary rainforests.

St. Louis encephalitis virus (SLEV) is the prototypic mosquito-transmitted flavivirus of the Americas. Unlike the West Nile virus, which we know was recently introduced into North America from the Old World, the provenience of SLEV is obscure. In an ecological investigation in a primary rainforest area of Palenque National Park, Mexico, we have discovered an ancestral variant of SLEV. The ancestral virus was much less active than the epidemic virus in cell cultures, reflecting its incomplete adaptation to hosts encountered outside primary rainforests. Knowledge of this virus enabled a spatiotemporal reconstruction of the common ancestor of all SLEVs and how the virus spread from there. We can infer that the cosmopolitan SLEV lineage emerged from Central America in the 17th century, a period of post-Columbian colonial history marked by intense human invasion of primary rainforests. Further spread followed major bird migration pathways over North and South America.

Intertwined arbovirus transmission activity: reassessing the transmission cycle paradigm

Arboviruses are emerging/reemerging infectious agents worldwide. The factors within this scenario include vector and host population fluctuations, climatic changes, anthropogenic activities that disturb ecosystems, an increase in international flights, human mobility, and genetic mutations that allow spill-over phenomenon. Arboviruses are maintained by biologic transmission among vectors and hosts. Sometimes this biological transmission is specific and includes one vector and host species such as Chikungunya (CHIKV), Dengue (DENV), and urban Yellow Fever (YFV). However, most of the arboviruses are generalist and they use many vectors and hosts species. From this perspective, arboviruses are maintained through a transmission network rather than a transmission cycle. This allows us to understand the complexity and dynamics of the transmission and maintenance of arboviruses in the ecosystems. The old perspective that arboviruses are maintained in close and stable transmission cycles should be modified by a new more integrative and dynamic idea, representing the real scenario where biological interactions have a much broader representation, indicating the constant adaptability of the biological entities.