West Nile Virus
West Nile virus (WNV) is a mosquito-borne virus that can cause mild illness (West Nile fever) or severe symptoms (encephalitis or meningitis - inflammation of the brain) in humans and other animals. People primarily get West Nile from the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds that carry the virus in their blood.
The key to preventing West Nile virus and other mosquito-related illnesses is to prevent mosquito bites and control mosquitoes in and around your home.
What To Know About West Nile Virus
- The chances you will become severely ill from any one mosquito bite are extremely small. Even in areas where mosquitoes do carry the virus, very few mosquitoes are infected.
- Hot, dry weather conditions can increase the virus cycle in birds and mosquitoes, particularly in urban/suburban areas. This can lead to a greater chance of human infection.
- August and September are the months of greatest risk to humans for becoming infected with WNV in Michigan.
- WNV will likely remain an issue in Michigan, causing the need for annual prevention efforts.
- Corvid species of birds (crows, ravens, and blue jays) are sensitive to the virus. Large numbers of dead birds in a particular geographic area can be a predictor of human infection.
- Culex species of mosquitoes are important in the transmission of WNV to humans. These mosquitoes must lay their eggs in water. They prefer water that is stagnant and nutrient-rich.
- For more information, see our West Nile Virus Fact Sheet (PDF).
Symptoms of West Nile Virus Infection
Most people infected with West Nile virus have no symptoms of illness, but some may become ill 3 to 15 days after the bite from an infected mosquito. Studies have shown that about 1 in 4 infected persons will experience mild illness with fever, headache and body aches, sometimes with a skin rash and swollen lymph glands.
Less than 1% of people who get bitten and become infected with West Nile virus will develop a severe illness like encephalitis or meningitis. The risk of getting West Nile encephalitis is higher in persons 50 years of age or older. More severe infection may be marked by convulsions, disorientation, headache, high fever, muscle weakness, stiff neck, or paralysis. In a few cases, mostly among the elderly, death may occur.
Dead Bird Reporting
Dead or sick birds, especially corvids (crows, ravens or blue jays), can indicate that West Nile virus is active in a particular area. To report a dead or sick bird, please enter the information on the State of Michigan Sick or Dead Bird and Mammal Reporting Website. The Washtenaw County Health Department does not test dead or sick birds for West Nile virus or any other diseases.
West Nile Virus Activity in Washtenaw County
| Year |
Human Cases: WNV Fever |
Human Cases: Neuroinvasive |
Human Deaths |
Positive Blood Donors |
Horse Cases |
Other Animal Cases |
|---|---|---|---|---|---|---|
| 2022 (as of 3/31/22) | 0 | 0 | 0 | 0 | 0 | 0 |
| 2021 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2020 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2019 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2018 | 0 |
1 | 0 | 0 | 0 | 3* |
| 2017 |
0 |
0 | 0 | 0 | 0 |
5 |
| 2016 |
0 |
2 |
0 |
0 |
0 |
1 |
| 2015 |
0 |
0 |
0 |
0 |
0 |
2 |
| 2014 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2013 |
0 |
1 |
0 |
0 |
0 |
0 |
| 2012 |
2 |
2 |
1 |
2 |
0 |
1 |
| 2011 |
0 |
0 |
0 |
N/A |
0 |
0 |
| 2010 |
1 |
1 |
0 |
N/A |
1 |
0 |
| 2009 |
0 |
0 |
0 |
N/A |
0 |
0 |
| 2008 |
0 |
0 |
0 |
N/A |
0 |
5 |
| 2007 |
0 |
0 |
0 |
N/A |
0 |
1 |
| 2006 |
1 |
0 | 0 | N/A | 2 | 12 |
| 2005 | 2 | 1 | 0 | N/A | 0 | 7 |
| 2004 | 0 | 0 | 0 | N/A | 3 | 7 |
| 2003 | 0 | 0 | 0 | N/A | 0 | 3 |
| 2002 | 1 | 0 | 0 | N/A | 6 | 1 |
See vector-borne disease data for Washtenaw County.