West Nile virus

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Electron micrograph of the West Nile virus
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Species	West Nile virus

West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the Flavivirus genus and belongs to the family Flaviviridae. The virus is primarily transmitted to humans through the bite of an infected mosquito, most commonly the Culex species.

Virology

Genome of the West Nile Virus

West Nile virus is an enveloped virus with a single-stranded, positive-sense RNA genome. The genome is approximately 11,000 nucleotides long and encodes a single polyprotein that is cleaved into three structural proteins (C, prM, and E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5).

The virus is closely related to other flaviviruses such as Dengue virus, Zika virus, and Yellow fever virus.

Transmission

WNV is primarily transmitted by mosquitoes, with birds serving as the main reservoir hosts. Humans and other mammals are considered dead-end hosts, as they do not develop high enough levels of viremia to infect mosquitoes. The virus can also be transmitted through blood transfusions, organ transplants, and from mother to child during pregnancy, delivery, or breastfeeding.

Epidemiology

West Nile virus was first identified in the West Nile district of Uganda in 1937. Since then, it has spread to many parts of the world, including Africa, Europe, the Middle East, North America, and West Asia. The first major outbreak in the United States occurred in 1999 in New York City.

Clinical Features

Most people infected with WNV are asymptomatic. Approximately 20% of infected individuals develop West Nile fever, which is characterized by fever, headache, tiredness, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash. Less than 1% of infected individuals develop severe neurological disease, such as encephalitis or meningitis, which can be fatal.

Diagnosis

Diagnosis of WNV infection is typically based on clinical symptoms and confirmed by laboratory testing. Serological tests, such as the detection of IgM antibodies in serum or cerebrospinal fluid, are commonly used. Reverse transcription polymerase chain reaction (RT-PCR) can also be used to detect viral RNA.

Prevention and Control

Preventive measures focus on reducing mosquito exposure. This includes using insect repellent, wearing long sleeves and pants, and eliminating standing water where mosquitoes breed. Public health efforts also include mosquito control programs and surveillance of bird populations.

Also see

• Flavivirus
• Mosquito-borne diseases
• Encephalitis
• Zika virus
• Dengue fever