West Nile Virus

Background

West Nile virus (WNV), an arthropod-borne flavivirus, was first detected in the Western Hemisphere in the New York City area in 1999 in an outbreak affecting people, horses and birds. Subsequent detections of WNV throughout the United States indicate the virus has spread rapidly. Although WNV can be transmitted from mosquitoes to certain mammals such as horses and humans, avian species are the most common hosts of the virus. The effects of WNV on North American bird populations have remained largely unknown until recently. By comparing predicted species abundance distributions to actual population surveys, there is now evidence suggesting that WNV has significantly reduced regional population growth rates in several avian species including crows, robins, black-capped chickadees, chipping sparrows, bluebirds, cardinals, tufted titmice, and white-breasted nuthatches (LaDeau, S.L., Kilpatrick, A. M. & Marra, P.P. West Nile virus emergence and large-scale declines of North American bird populations. Nature 447, 710-713, 2007).

In Wisconsin, WNV has been identified since summer 2002. Surveillance for wild bird morbidity and mortality appears to be one of the most sensitive early detection systems for WNV. The virus can infect a wide range of bird species, with corvids (crows, jays, and ravens) being highly susceptible to WNV. Once a highly susceptible bird becomes infected with WNV, death can occur within five to seven days. Dead birds are most often found singly in one place at one time, not in mass die-offs. As WI public health surveillance has focused on corvids, the majority of the WNV-positive birds detected have been corvids. WNV-related deaths, however, have also been documented in bald eagles, goshawks, Cooper’s, sharp-shinned, and red-tailed hawks, robins, bluebirds, mourning doves, cardinals, chickadees, and gray squirrels. Other WI wildlife with evidence of exposure to WNV include tundra swan, sandhill and whooping cranes, double-crested cormorant, sora rail, hairy and downy woodpeckers, grackle, cedar waxwing, wild turkey, big and little brown bat, elk, coyote, and gray wolf.

Additional Information

• WNV Surveillance
• WNV and Wetlands [PDF 234KB]
• WNV and Wild Game Birds (USGS) [exit DNR]

Related Sites

• Audubon Society WNV [exit DNR]
• National Wildlife Health Center [exit DNR]
• Centers for Disease Control [exit DNR]
• Environmental Protection Agency (Mosquito Control) [exit DNR]
• U.S. Department of Agriculture [exit DNR]
• WI Division of Public Health [exit DNR]

To report a dead bird please contact the Wisconsin Dead Bird Hotline at 1-800-433-1610.

Questions for Wildlife Management