West Nile Virus

West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family Flaviviridae, specifically from the genus Flavivirus, which also contains the Zika virus, Dengue virus, and Yellow fever virus. West Nile virus is primarily transmitted by mosquitoes, mostly species of Culex. The primary hosts of WNV are birds, so that the virus remains within a “bird–mosquito–bird” transmission cycle.

WNV is a positive-sense, single-stranded RNA virus. Its genome is approximately 11,000 nucleotides long and is flanked by 5′ and 3′ non-coding stem loop structures. The coding region of the genome codes for three structural proteins and seven nonstructural (NS) proteins, proteins that are not incorporated into the structure of new viruses. The WNV genome is first translated into a polyprotein and later cleaved by virus and host proteases into separate proteins (i.e. NS1, C, E).

In humans, West Nile virus can cause a disease known as West Nile fever. According to the U.S. Centers for Disease Control and Prevention, approximately 80% of infected people have few or no symptoms, around 20% of people develop mild symptoms, such as fever, headache, vomiting, or a rash, while less than 1% of people develop severe symptoms, such as encephalitis or meningitis with associated neck stiffness, confusion, or seizures. The risk of death among those in whom the nervous system is affected is about 10%. Recovery may take weeks to months. Risks for severe disease include age over 60 and other health problems. Historically, people in areas where the virus was endemic, such as the Nile Delta, usually experienced subclinical or mild disease. Diagnosis is typically based on symptoms and blood tests. While there is no specific treatment, pain medications may be useful.

Twenty years of West Nile Virus in the Americas (last updated 30 Oct 2019)

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