WISCONSIN -- The Wisconsin Department of Health Services (DHS) has confirmed the first West Nile virus (WNV) activity in the state this year. A human case of WNV illness has been reported in a resident of Barron County, and mosquitos collected from Milwaukee and Lafayette Counties have tested positive for WNV.
"The first detections of West Nile virus this year are a reminder to take steps to prevent mosquito bites and possible disease. West Nile virus poses a risk to all Wisconsinites, but people who have weakened immune systems are at higher risk for serious illness," said Paula Tran, State Health Officer and Administrator of the Division of Public Health.
WNV is spread to humans, birds, and other animals through the bite of an infected mosquito. Mosquitoes get WNV by feeding on infected birds. The virus is not spread directly from person to person, animal to animal, or animal to person.
Most people who are infected with WNV do not have symptoms. Those who become ill with WNV may experience fever, chills, headache, muscle aches, rash, and fatigue. Some people will develop severe illness with symptoms that include high fever, muscle weakness, stiff neck, disorientation, mental confusion, tremors, paralysis, seizure, and coma. Older adults and people who have compromised immune systems are at greater risk of developing severe illness that can be fatal. It is important that people contact a health care provider if they suspect they have WNV illness.
DHS has monitored WNV since 2001, tracking confirmed cases in mosquitoes, animals, and humans across the state in order to alert health care providers and Wisconsinites about risk. An average of 18 cases of WNV illness are reported among Wisconsin residents each year. WNV cases in humans have been reported from June through November; however, most people with WNV report becoming ill in August and September.
Related: DNR Concludes Efforts To Trap Black Bear Involved In Barron County Attack
The best way to avoid illnesses spread by mosquitoes is to reduce exposure to them and eliminate mosquito breeding sites. Mosquito activity and the risk of WNV will continue through the rest of the summer until there is a hard frost (temperatures below 28 degrees Fahrenheit for at least four straight hours).
Last Update: Jul 28, 2025 12:22 pm CDT
