State’s 3rd human West Nile Virus case of 2025 confirmed in DuPage County

DUPAGE COUNTY, Ill. — Health officials in DuPage County have confirmed the county’s first human case of West Nile Virus this year, the third confirmed case statewide in 2025.

Health officials from the DuPage County Health Department (DCHD) confirmed Thursday that the county’s first human case of West Nile Virus (WNV) had been detected in a resident in Glen Ellyn.

The resident who contracted the case is in their 50s and began experiencing symptoms in mid-July.

Health officials in the county have since moved the Personal Protection Index (PPI) risk level from one to two, which indicates high numbers of infected mosquitoes in most areas in the county, with at least one human case.

County health officials are now urging residents to take precautions to avoid contracting WNV.

“With a rise in recent weeks in mosquito batches testing positive for the presence of WNV, DCHD is encouraging residents to stay safe outdoors by protecting themselves from mosquito bites and the risk of contracting WNV,” health officials said in a news release sent out on Thursday.

The human case came a little under two months after the first WNV-positive mosquito batches were located in the county.

Just last week, health officials in Lake County confirmed the state’s second case of West Nile Virus for 2025.

Officials say WNV usually peaks during the late summer, between July and September, when the mosquito population is at its peak. WNV activity generally decreases in the fall when cooler temperatures arrive.

The PPI is updated each Wednesday at 3 p.m. throughout West Nile Virus (WNV) season as officials continue to collect and test mosquitoes in traps around the county.

West Nile Virus in Illinois

As of 12:30 p.m.. Thursday, the West Nile Virus dashboard, maintained by the Illinois Department of Public Health, showed two cases, though health officials around the state have confirmed three cases.

In total, 40 counties around Illinois have seen at least one positive WNV case in a human, bird, mosquito or horse.

In 2024, the state saw 69 human cases, which resulted in 13 deaths.

Where have West Nile Virus-positive mosquitoes been found in the Chicagoland this season?

While only three human cases have been reported so far this year, health officials from around the state have identified dozens of WNV-positive mosquito batches.

Back in Early June, health officials in McHenry County announced that they identified a batch that tested positive for West Nile Virus in Lake in the Hills.

It was the first WNV-positive mosquito batch located in the county so far this year.

Just a week before, health officials said mosquitoes from a batch found in Glenview tested positive for the virus.

Officials did not specify a specific area where the batch was pulled from.

In mid-June, health officials in Cook County identified a WNV-positive mosquito batch in Chicago.

How to avoid West Nile Virus

According to health officials, while there is no vaccine currently available for WNV, there are steps people can take to reduce the likelihood of contracting WNV.

While West Nile virus can be transmitted through blood transfusions and organ transplants, it is most commonly transmitted to humans through the bite of an infected mosquito.

The Illinois Department of Public Health advises residents to adhere to the following guidelines to minimize the risk of WNV exposure:

• Reduce – Residents should work to ensure that doors and windows have tight-fitting screens and should repair or replace any that have tears or openings. Residents should also work to keep doors and windows shut.

• Repel – Residents are advised to wear shoes, socks, long pants and a light-colored, long-sleeved shirt, as well as apply an EPA-registered insect repellent that contains DEET, picaridin, oil of lemon eucalyptus, or IR 3535 when outside.

The CDC notes that parents should consult a physician before using repellents on children under three.

• Report – Residents are advised to report locations where they see sitting stagnant for more than a week. If reported soon enough, the local health department or city government may be able to add larvicide to the water, to kill any mosquito larvae.

West Nile Virus symptoms

The Centers for Disease Control and Prevention say about eight in 10 people infected with WNV do not develop symptoms.

Around one in five people who become infected develop a fever, headache, body aches, joint pains, vomiting, diarrhea or rash. Most who develop these symptoms are able to completely recover, but CDC officials say fatigue and weakness can last for weeks or months.

According to the CDC, only about 1 in 150 people will develop a severe illness that impacts the central nervous system.

Officials said symptoms of severe illness usually include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.

While WNV can cause severe illness in people of any age, people over the age of 60 and those with certain medical conditions are also at greater risk.

Those who suffer severe illness could take several weeks or months to recover and the CDC said some effects may be permanent.