Portal:Viruses/Selected virus/9

West Nile virus (WNV) is a flavivirus, an RNA virus in the Flaviviridae family. The enveloped virion is 45–50 nm in diameter and contains a single-stranded, positive-sense RNA genome of around 11,000 nucleotides, encoding ten proteins. The main natural hosts are birds (the reservoir) and several species of Culex mosquito (the vector). WNV can also infect humans and some other mammals, including horses, dogs and cats, as well as some reptiles. Transmission to humans is generally by bite of the female mosquito. Mammals form a dead end for the virus, as it cannot replicate sufficiently efficiently in them to complete the cycle back to the mosquito.

First identified in Uganda in 1937, WNV was at first mainly associated with disease in horses, with only sporadic cases of human disease until the 1990s. The virus is now endemic in Africa, west and central Asia, Oceania, the Middle East, Europe and North America. A fifth of humans infected experience West Nile fever, a flu-like disease. In less than 1% of those infected, the virus invades the central nervous system, causing encephalitis, meningitis or flaccid paralysis. No specific antiviral treatment has been licensed and only a veterinary vaccine is available. Mosquito control is the main preventive measure.