What is West Nile virus?

A species of FLAVIVIRUS, one of the Japanese encephalitis virus group (ENCEPHALITIS VIRUSES, JAPANESE), which produces encephalitis experimentally when inoculated into some rodents, chicks, birds, or monkeys. In humans, it is seen most frequently in Africa, Asia, and Europe presenting as a silent infection or undifferentiated fever (WEST NILE FEVER). It is transmitted by CULEX spp mosquitoes.