Volume 10, Number 6—June 2004 Antibody Prevalence of West Nile
Virus in Birds, Illinois, 2002 Antibodies to West Nile virus
were detected in 94 of 1,784 Illinois birds during 2002. Captive
and urban birds had higher seropositivity than did birds from
natural areas, and northern and central Illinois birds’
seropositivity was greater than that from birds from the
southern sites. Adult and hatch-year exposure rates did not
differ significantly. West Nile virus (WNV; family Flaviviridae,
genus Flavivirus) was first identified in the Western Hemisphere
in 1999 (1) and had been detected in 27 states of the United
States by the end of 2001 (2). Despite abundant evidence of
avian, mosquito, and mammalian transmission (2), few reports are
available on the exposure of live birds to WNV outside of New
York and New Jersey. WNV activity was first detected in Illinois
in September 2001 (3). During 2001, its distribution was limited
to seven counties, primarily in northeastern Illinois (3). In
2002, however, Illinois had th