History of West Nile Virus
West Nile virus is an emerging infectious disease that was first discovered in the African country of Uganda in 1937, and in recent years has spread beyond its traditional boundaries, causing illness in birds, horses, and humans in Europe and now the United States. It was first discovered in the U.S. in 1999 in New York City. Since that time, WNV has been detected in humans, animals, and mosquitoes in 47 states from coast to coast.
In response to the threat of WNV to Michigan, in 2000 the WNV Working Group emerged from the Arbovirus Core Group. In 2001, a toll-free hot line was established for citizens to report dead crows, as monitoring death amongst these birds can be an early indicator of virus activity in an area. Information was collected as to the location and condition of these birds, and appropriate birds were collected for testing. As a result of this effort, WNV was first detected in Michigan in August 2001, in dead crows. There were 65 WNV-positive birds detected in 10 counties including Wayne, Oakland, Macomb, Washtenaw, Jackson, Calhoun, Ingham, Barry, Ottawa, and Muskegon. In addition, 3 WNV positive mosquito pools 3 were detected in Oakland (2) and Macomb (1) counties.
This surveillance system was continued in 2002 and WNV was first detected in a dead crow from Wayne County that was confirmed to be infected with the virus on May 24, 2002. Testing of dead corvids (crows, blue jays, and ravens) was conducted from May-October. Bird testing ended October 31, 2002 with 73 of 83 Michigan counties in both the Upper and Lower Peninsulas having WNV positive birds detected. In addition to birds, there were 341 confirmed cases of WNV in horses in 45 counties in both the Upper and Lower Peninsula of Michigan. WNV is now considered to be endemic to the state.
Limited mosquito surveillance in 2002 revealed 58 positive mosquito pools in 7 of 9 counties surveyed in the Lower Peninsula of Michigan. The counties with positive mosquito pools identified were Wayne, Oakland, Macomb, Ingham, Saginaw, Tuscola, and Midland. The majority of these were Culex species, the most common mosquito in Michigan to be associated with WNV transmission. In addition, a positive Coquillettidia perturbans pool was detected for the first time in the state in 2002. This species may be important as a potential bridge vector as it bites both birds and mammals.
In 2002, Michigan as well as other Great Lakes states experienced the first documented cases of WNV in humans in this region. The first 2 cases in Michigan were reported on August 16, 2002. Although transmission of WNV ended with the first hard frost in mid-October, laboratory testing of samples continued into November and December. The Michigan Department of Community Health Laboratory received over 2900 specimens for WNV testing in 2002. Of these, there were a total of 644 laboratory positive specimens.
For 2003, a system for web-based reporting of dead birds was developed. This has allowed for rapid reporting of dead bird sightings, and has provided a means of collecting appropriate birds for WNV testing. In 2003 this web reporting form was used over 5,000 times to report death and illness in nearly 7,000 birds and mammals, 1,800 of which were corvid species. On May 5, 2003 the first positive corvid was confirmed from Lenawee county. A total of 89 corvids, from 75 zip codes, located in 33 counties tested positive. The first human case occurred in early September and was followed by 18 additional cases in Huron, Ingham, Macomb, Oakland and Wayne counties.
The first WNV positive crow in 2004 was detected on May 10th. The crow was collected from Saginaw Co. Over 700 corvids were tested from April 1st through October 31st, with a total of 245 corvids testing positive. The positive birds were collected from 57 counties in both the upper and lower peninsula. Some mosquito surveillance continued in 2004, as well, detecting 69 positive mosquito pools from 7 counties with the majority of positive mosquitoes being Culex species. Finally, the first human case of WNV occurred at the end of June in a person from Kalamazoo county. An additional 15 human cases were reported from Wayne, Kent, Tuscola, Oakland, and Branch counties.
The first WNV positive corvid in 2005 was detected on May 13th. The blue jay was collected from Washtenaw Co. Over 303 corvids were tested from April 1st through October 31st, with a total of 131 corvids testing positive. The positive birds were collected from 23 counties in both the upper and lower peninsula. Some mosquito surveillance continued in 2004, as well, detecting 55 positive mosquito pools from 8 counties with the majority of positive mosquitoes being Culex species. Finally, the first three human cases of WNV occurred on August 26th from Grand Traverse, Kent, and Wayne counties. An total 62 human cases were reported for the year.
Testing during 2006 was conducted the same as the past three years, based on zip codes in order to provide community-based information about WNV activity in birds. In 2007, funding for WNV was substantially reduced. Testing was still be conducted for humans, for corvids by certain county level Health Departments and for select wildlife at the MDNR. Until there is a change in the status of the funding surveillance will continue in this manner in future years. Information about dead bird sightings will continue to be important. Calculations of the number of dead birds per square mile in a county can be used to estimate the level of risk for human infection in that area. Communities can use this information to target their intervention and prevention strategies to areas where WNV activity has been detected. To report a dead or sick bird or mammal in your area please visit our on-line reporting form: Report a Sick or Dead Bird or Mammal
Please visit our Testing, Tables and Maps Section for the most up-to-date results of Michigan's WNV surveillance efforts.