A species of FLAVIVIRUS, one of the Japanese encephalitis virus group (ENCEPHALITIS VIRUSES, JAPANESE). It can infect birds and mammals. In humans, it is seen most frequently in Africa, Asia, and Europe presenting as a silent infection or undifferentiated fever (WEST NILE FEVER). The virus appeared in North America for the first time in 1999. It is transmitted mainly by CULEX spp mosquitoes which feed primarily on birds, but it can also be carried by the Asian Tiger mosquito, AEDES albopictus, which feeds mainly on mammals.

Any viral organism that can be assigned to the species West Nile virus.

Transmitted by Culex spp mosquitos; agent of emerging disease in North America.

West Nile virus is a flavivirus that is now the primary cause of arbovirus encephalitis in the US. Most patients have mild or no symptoms. About 1 out of 150 patients develop a severe infection involving the central nervous system. Diagnosis is by serologic testing. Treatment is supportive with close monitoring for severe infection.

The West Nile virus is one of the many members of the genus Flavivirus that are known to cause human disease. The life cycle of the West Nile virus involves the microbe's transmission from nonhuman animals to humans by way of Aedes, Culex, or Anopheles mosquitoes.

A mosquito-transmitted virus causes most cases of West Nile infection. Most people infected with West Nile virus either don't develop signs or symptoms or have only minor ones, such as fever and mild headache. However, some people develop a life-threatening illness that includes inflammation of the spinal cord or brain.

West Nile virus (WNV) is an infection caused by a flavivirus, which in most cases is asymptomatic, but can cause a self-limited influenza-like illness (West Nile fever or WNF) and, rarely, West Nile neuroinvasive disease (WNND).