Illinois has reported its first human case of West Nile virus (WNV) for 2025, confirmed in a Southern Illinois resident who was hospitalized with complications from the infection. According to the Illinois Department of Public Health (IDPH), this is the earliest onset of illness recorded in the state since 2016.
West Nile virus is spread by mosquitoes and can lead to severe health problems in some cases. About one in 150 people who contract WNV may develop serious conditions affecting the brain, spinal cord, or nerves, which can sometimes result in paralysis.
As of June 24, WNV has been detected in 19 counties across Illinois. The first mosquito batch testing positive for WNV this year was found on May 9 in Rockford. In comparison, last year saw 69 confirmed human cases and 13 deaths from the virus, marking the highest death toll since 2018.
“The fact that we are seeing the first human case of West Nile virus so early in the season serves as a timely reminder – especially for seniors and those with weakened immune systems – to protect yourself from illnesses caused by mosquito bites,” said IDPH Director Dr. Sameer Vohra. “I encourage all Illinoisans to ‘Fight the Bite’ and take precautions to protect themselves and their loved ones.”
The IDPH recommends several measures to reduce risk: ensuring doors and windows have tight-fitting screens, removing standing water where mosquitoes breed, wearing protective clothing outdoors, using EPA-registered insect repellents, and reporting stagnant water sites to local authorities for possible treatment with larvicide.
A county is considered positive for WNV if any mosquito, horse, or human tests positive for the virus. This year’s affected counties include Bureau, Christian, Clinton, Cook, DeKalb, DuPage, Fulton, Grundy, Hancock, Henry, Marshall, McDonough, McHenry, Peoria, Scott, Stark, Tazewell, Wayne and Winnebago. In 2024, WNV was identified in 72 counties statewide.
The state supports local mosquito control by providing $2.8 million to local health departments for surveillance and control activities such as purchasing larvicide and investigating mosquito breeding sites. Local agencies collect mosquitoes for testing as part of ongoing monitoring efforts.
West Nile virus is primarily transmitted through bites from infected house mosquitoes that have fed on birds carrying the virus. While most infected people do not experience symptoms or only mild ones such as fever or headache lasting a few days to weeks, those over age 60 or with compromised immune systems face greater risk of severe illness or death.
For more details about West Nile virus visit https://www.cdc.gov/westnile/index.html.
