WNV Significance

West Nile virus (WNV) activity was first detected in Michigan in 2001, when 65 WNV positive corvids (crows, blue jays and ravens) were discovered in 10 counties.  In 2002, WNV was confirmed in corvids from 73 of the 83 counties in Michigan.  In addition to corvids,  18 non-corvid birds and mammals were confirmed positive including several great-horned owls, hawks, house finches, a squirrel, a Canadian goose and a cedar waxwing.  341 cases of WNV in horses from 45 counties were confirmed, and the first human cases of WNV in Michigan were documented.  A total of 644 humans from 28 counties were positive for WNV in 2002, and 51 human deaths were attributed to the virus. WNV is now considered to be endemic in the state.  Human illness due to WNV continues to be detected every summer.

Early experience with West Nile virus in New York demonstrated that corvids (crows and blue jays) were more sensitive to the virus than other avian species, and more likely to die as a result of their infection. Monitoring death amongst these birds can be an early indicator of virus activity in an area. In 2003, a system for web-based reporting of dead birds was developed and continues to be in use for dead bird reporting. This allows for rapid reporting of dead bird sightings, and provides a means of collecting appropriate birds for WNV testing. Communities can use this information to target their intervention and prevention strategies to areas where WNV activity has been detected.

Although crows and blue jays account for between 50 and 90 percent of reported avian cases, WNV infection has been identified in over 280 other avian species during the North American outbreak. The list includes over 200 native North American birds and over 50 exotic and zoo species. Migrating birds carrying WNV in their blood have had a significant impact on the spread of the virus across the United States.  During the summer of 2002, significant numbers of raptor species (owls, hawks, eagles and vultures), especially in the Midwestern United States, were found to be infected with the virus. Many mammalian wildlife species have also been shown to be positive for WNV. The web-based reporting form has allowed for the reporting of all species of wildlife, and over time will be used to determine a normal baseline wildlife mortality figure.

Please visit our Testing, Tables and Maps section for the most up-to-date testing results for Michigan as well as historical WNV data from 2001-present.

The CDC website also has current nation wide data on human testing results:

http://www.cdc.gov/ncidod/dvbid/westnile/surv&control.htm