[West Nile fever].

Reviews the data on the history, distribution, ecology, epidemiology, and clinical picture of West Nile (WN) fever and the ecology of the virus (Flaviviridae, Flavivirus, Japanese encephalitis complex). Analyzes the causes of sudden epidemic outbreaks with high mortality in Rumania in 1996, in European Southern Russia, and in New York and its environs in 1999. Offers recommendations on decreasing the damage inflicted by new and emerging infections leading to epidemic emergencies.