Emerging arboviral encephalitis

Newsworthy in the W est but much more common in the East

The recent outbreaks of West Nile encephalitis in New York and Israel are drawing the western world's attention to the potential threat of arthropod-borne virus (arbovirus) encephalitis.1 But in many parts of Asia, infection with West Nile virus's sister, Japanese encephalitis virus, is a daily reality.

Epidemics of encephalitis were described in Japan from the 1870s onwards, and Japanese encephalitis virus was first isolated from a fatal case in the 1930s.2 West Nile virus was isolated from the blood of a febrile woman in Uganda a few years later in 1937.3 Both viruses are small enveloped RNA viruses, members of the genus Flavivirus (family Flaviviridae), named after the prototype yellow fever virus (flavus is the Latin for yellow). The flaviviruses are relatively new viruses, derived from a common ancestor 10-20 000 years ago, that are rapidly evolving to fill new ecological niches.4 Both West Nile and Japanese encephalitis virus are transmitted in an enzootic cycle between small birds by Culex mosquitoes, though for Japanese encephalitis …