West Nile virus is a neurotropic flavivirus that has emerged globally as a primary cause of viral encephalitis. Infection of humans and other vertebrate animals is associated with a febrile illness that can progress to a lethal encephalitis or flaccid paralysis syndrome. Its appearance in the Western Hemisphere in 1999 and the corresponding increase in global disease burden over the last decade have been accompanied by intensive study, including the entry of many scientists into the field. Breakthroughs have been made in understanding the unique transmission pattern between the vector and the...