First 2026 Human Case of West Nile Virus in Illinois Confirmed

First 2026 Human Case of West Nile Virus in Illinois Confirmed

IDPH reminds Illinoisans to "Fight the Bite" and prevent illness carried by mosquitoes

SPRINGFIELD - The Illinois Department of Public Health (IDPH) has confirmed the first human case of West Nile virus (WNV) in Illinois for 2026. The confirmed case involves a resident of Piatt County. In addition, IDPH has identified three other probable human cases of WNV from northern Illinois. About one in five people who contract the disease caused by a bite from an infected mosquito may develop common symptoms, including fever, headache, body aches, joint pain, or other potentially serious complications.

So far in 2026, WNV has been observed in 50 Illinois counties with either a mosquito pool, horse and/or human from that county testing positive for the virus. The full list of counties where West Nile virus has been detected in mosquito batches can be found at West Nile Virus in Illinois - Surveillance.

In 2025, WNV was found in 73 Illinois counties. There was a total of 150 human cases, with ten deaths linked to the virus.

"For many Illinois residents, summer means lots of time spent outdoors enjoying everything our state has to offer," said IDPH Director Dr. Sameer Vohra. "Before heading outside, it's important to take steps to protect yourself and loved ones from mosquito bites and the illnesses they can spread. Applying insect repellant, wearing long, loose clothing, and reporting stagnant water to your local health department can help lower the risk of contracting diseases like West Nile Virus."

IDPH urges the public to Fight the Bite by practicing the three "R's" - reduce, repel, and report:

• REDUCE - make sure doors and windows have tight-fitting screens. Repair or replace screens that have tears or other openings. Try to keep doors and windows shut. Eliminate, or refresh each week, all sources of standing water where mosquitoes can breed, including water in bird baths, ponds, flowerpots, wading pools, old tires, and any other containers.
• REPEL - when outdoors, wear shoes and socks, long pants and a light-colored, long-sleeved shirt, and apply an EPA-registered insect repellent that contains DEET, picaridin, oil of lemon eucalyptus, IR 3535, para-menthane-diol (PMD), or 2-undecanone according to label instructions. Consult a physician before using repellents on infants.
• REPORT - report locations where you see water sitting stagnant for more than a week such as roadside ditches, flooded yards, and similar locations that may produce mosquitoes. The local health department or city government may be able to add larvicide to the water, which will kill any mosquito larvae.

IDPH supports mosquito control efforts throughout the state by providing $2.8 million in funding to Illinois' 97 local health departments for vector surveillance and control activities. This includes purchasing and applying larvicide, working with municipal governments and local news media for WNV prevention and education, and investigating mosquito production sites and nuisance mosquito complaints. Local health departments collect mosquitoes for West Nile virus testing.

Monitoring for WNV in Illinois includes tests for mosquito batches, as well as testing sick horses and humans with West Nile virus-like symptoms.

West Nile virus is transmitted through the bite of a Culex mosquito, commonly called a house mosquito, that has picked up the virus by feeding on an infected bird. Common symptoms include fever, nausea, headache and muscle aches. Symptoms may last from a few days to a few weeks. Most people infected with West Nile virus will not show any symptoms; however, in rare cases it can lead to severe illness including paralysis, meningitis or encephalitis (i.e. brain and nerve infections), or even death. People older than 60 and those with weakened immune systems are at highest risk for severe illness.

Click here for additional information about West Nile virus.