Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States

In Late summer 1999, an outbreak of human encephalitis occurred in the nort heastern United States that was concurrent with extensive mortality in crow s (Corvus species) as well as the deaths of several exotic birds at a zoolo gical park in the same area. Complete genome sequencing of a flavivirus iso lated from the brain of a dead Chilean flamingo (Phoenicopterus chilensis), together with partial sequence analysis of envelope glycoprotein (E-glycop rotein) genes amplified from several other species including mosquitoes and two fatal human cases, revealed that West Nile (WN) virus circulated in na tural transmission cycles and was responsible for the human disease. Antige nic mapping with E-glycoprotein-specific monoclonal antibodies and E-glycop rotein phylogenetic analysis confirmed these viruses as WN. This North Amer ican WN virus was most closely related to a WN virus isolated from a dead g oose in Israel in 1998.