Since its initial isolation in Uganda in 1937 through the present, West Nile virus (WNV) has become an important cause of human and animal disease worldwide. WNV, an enveloped virus of the genus Flavivirus, is naturally maintained in an enzootic cycle between birds and mosquitoes, with occasional epizootic spillover causing disease in humans and horses. The mosquito vectors for WNV are widely distributed worldwide, and the known geographic range of WNV transmission and disease has continued to increase over the past 77 years. While most human infections with WNV are asymptomatic, severe neurological disease may develop resulting in long-term sequelae or death. Surveillance and preventive measures are an ongoing need to reduce the public health impact of WNV in areas with the potential for transmission.

/pdf/the-global-ecology-and-epidemiology-of-west-nile-virus-xhb3d6xgpv.pdf

The global ecology and epidemiology of West Nile virus.

It has been 20 years since West Nile virus first emerged in the Americas, and since then, little progress has been made to control outbreaks caused by this virus. After its first detection in New York in 1999, West Nile virus quickly spread across the continent, causing an epidemic of human disease and massive bird die-offs. Now the virus has become endemic to the United States, where an estimated 7 million human infections have occurred, making it the leading mosquito-borne virus infection and the most common cause of viral encephalitis in the country. To bring new attention to one of the most important mosquito-borne viruses in the Americas, we provide an interactive review using Nextstrain: a visualization tool for real-time tracking of pathogen evolution (nextstrain.org/WNV/NA). Nextstrain utilizes a growing database of more than 2,000 West Nile virus genomes and harnesses the power of phylogenetics for students, educators, public health workers, and researchers to visualize key aspects of virus spread and evolution. Using Nextstrain, we use virus genomics to investigate the emergence of West Nile virus in the U S, followed by its rapid spread, evolution in a new environment, establishment of endemic transmission, and subsequent international spread. For each figure, we include a link to Nextstrain to allow the readers to directly interact with and explore the underlying data in new ways. We also provide a brief online narrative that parallels this review to further explain the data and highlight key epidemiological and evolutionary features (nextstrain.org/narratives/twenty-years-of-WNV). Mirroring the dynamic nature of outbreaks, the Nextstrain links provided within this paper are constantly updated as new West Nile virus genomes are shared publicly, helping to stay current with the research. Overall, our review showcases how genomics can track West Nile virus spread and evolution, as well as potentially uncover novel targeted control measures to help alleviate its public health burden.

/pdf/twenty-years-of-west-nile-virus-spread-and-evolution-in-the-4m6t98627o.pdf

Twenty years of West Nile virus spread and evolution in the Americas visualized by Nextstrain.

Background Serological evidence of West Nile virus (WNV) infection has been reported in different regions of Brazil from equine and human hosts but the virus had never been isolated in the country. Objectives We sought to identify the viral etiology of equine encephalitis in Espirito Santo state. Methods We performed viral culture in C6/36 cells, molecular detection of WNV genome, histopathology and immunohistochemistry from horse cerebral tissue. We also carried out sequencing, phylogenetic analysis and molecular clock. Findings Histopathologic analysis from horse cerebral tissue showed injury related to encephalitis and WNV infection was confirmed by immunohistochemistry. The virus was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) from brain tissue and subsequently isolated in C6/36 cells. WNV full-length genome was sequenced showing the isolated strain belongs to lineage 1a. The molecular clock indicated that Brazilian WNV strain share the same common ancestor that were circulating in US during 2002-2005. Main conclusions Here we report the first isolation of WNV in Brazil from a horse with neurologic disease, which was clustered into lineage 1a with others US WNV strains isolated in beginning of 2000's decade.

/pdf/first-isolation-of-west-nile-virus-in-brazil-4ewtpo8che.pdf

First isolation of West Nile virus in Brazil

Japanese encephalitis virus (JEV), which belongs to the genus Flavivirus of the family Flaviviridae, is a leading cause of meningo-encephalitis in Asian countries. The flavivirus non-structural protein 1 (NS1) plays a role in virus replication and in the elicitation of an immune response. The NS1′ protein found among the members of the JEV subgroup is an extended form of NS1 and is generated by a −1 ribosomal frameshift. This protein is known to be involved in viral pathogenicity; however, its specific function is still unknown. Here, we describe an investigation of the molecular function of NS1′ protein through the production of JEV NS1′-expressing and -non-expressing clones and their infection of avian and mammalian cells. Efficient NS1′ protein expression was observed in avian cells and was found to facilitate JEV production in both avian cultured cells and embryonated chicken eggs. NS1′ protein was observed to co-localize with NS5 protein and resulted in increased viral RNA levels in avian cells. These findings clearly indicate that NS1′ enhances the production of JEV in avian cells and may facilitate the amplification/maintenance role of birds in the virus transmission cycle in nature.

NS1' protein expression facilitates production of Japanese encephalitis virus in avian cells and embryonated chicken eggs.

Background: West Nile virus (WNV) was first sequenced in Brazil in 2019, when it was isolated from a horse in the Espirito Santo state. Despite multiple studies reporting serological evidence suggestive of past circulation since 2004, WNV remains a low priority for surveillance and public health, such that much is still unknown about its genomic diversity, evolution, and transmission in the country. Methods: A combination of diagnostic assays, nanopore sequencing, phylogenetic inference, and epidemiological modeling are here used to provide a holistic overview of what is known about WNV in Brazil. Results: We report new genetic evidence of WNV circulation in southern (Minas Gerais, Sao Paulo) and northeastern (Piaui) states isolated from equine red blood cells. A novel, climate-informed theoretical perspective of the potential transmission of WNV across the country highlights the state of Piaui as particularly relevant for WNV epidemiology in Brazil, although it does not reject possible circulation in other states. Conclusion: Our output demonstrates the scarceness of existing data, and that although there is sufficient evidence for the circulation and persistence of the virus, much is still unknown on its local evolution, epidemiology, and activity. We advocate for a shift to active surveillance, to ensure adequate preparedness for future epidemics with spill-over potential to humans.

West Nile Virus in Brazil

Serum samples from a total of 71 healthy captive birds belonging to 18 species were collected in July of 2008 in Medellin (Colombia) and tested for flaviviruses. Eighteen of 29 samples from American Flamingoes (Phoenicopterus ruber) were positive for West Nile virus (WNV) by reverse transcription-polymerase chain reaction. Selected positive samples were serially passaged and WNV was confirmed by immunofluorescence. Two isolates (524/08, 9835/08) were characterized in vitro and in vivo. Sequence analysis revealed WNV with 16 nucleotide substitutions resulting in six amino acid changes when compared with the NY99 strain. Colombian (COL) viruses were more closely related to Louisiana isolates from 2001. When compared with attenuated strains isolated from Texas, COL isolates differed in their plaque size and temperature sensitivity phenotype. The COL viruses were pathogenic in embryonated chicken eggs and Balb/c mice.

/pdf/characterization-of-west-nile-viruses-isolated-from-captive-5d7ijecbhv.pdf

Characterization of West Nile Viruses Isolated from Captive American Flamingoes (Phoenicopterus ruber) in Medellin, Colombia

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Characterization of West Nile Viruses Isolated from Captive American Flamingoes (Phoenicopterus ruber) in Medellin, Colombia