Chicago reported three human cases of West Nile virus in the last month as city officials warn the risk of contracting the virus is “high,” with more mosquitoes testing positive than usual.
The cases, reported in people between the ages of 40 and 80, were discovered in residents on Chicago’s Northwest and South Sides. Each began seeing symptoms in late July and early August.
“We are seeing a higher proportion of mosquitoes testing positive for West Nile virus than usual this year,” CDPH Commissioner Olusimbo “Simbo” Ige said in a statement.
Chicago routinely sprays insecticide across the city to kill mosquitoes and will be continuing that protocol in seven neighborhoods Wednesday and Thursday, following the most recent cases.
“West Nile virus risk in Chicago is currently rated as high, and all Chicagoans are encouraged to take precautions against mosquitoes,” CPDH said in an alert.
Here’s what to know:
Where have human cases of West Nile been confirmed?
The Illinois Department of Public Health confirmed the first human case of the virus in the state on June 24 in Southern Illinois. The Centers for Disease Control and Prevention confirmed a person hospitalized in the region marked the first human case of West Nile in 2025 for Illinois.
“The case marks the earliest onset of illness observed in Illinois since 2016, and underscores the risk posed by mosquito bites, especially to those who are over 65 or immunocompromised,” the health department said in a release.
Other human cases were reported in DuPage and Lake Counties in the Chicago area as of data from July 25, in addition to the three Chicago cases now confirmed.
Last year, 69 human cases of West Nile were reported, leading to 13 deaths, the highest number of deaths related to the virus 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,” IDPH Director Dr. Sameer Vohra said in a statement. “I encourage all Illinoisans to ‘Fight the Bite’ and take precautions to protect themselves and their loved ones.”
What’s happening in Chicago?
CDPH will spray several communities Wednesday and Thursday to kill mosquitoes, that includes Forest Glen, Norwood Park, Mount Greenwood, Beverly, East Garfield Park, Near West Side and North Lawndale.
The sprays, weather permitting, will begin at dusk and continue through 1 a.m. “with licensed mosquito abatement technicians dispensing an ultra-low-volume spray from trucks.”
What is West Nile virus?
West Nile Virus is a mosquito-borne virus that infects the brain. It is a close relative of St. Louis encephalitis. It is commonly found in Africa, West Asia and the Middle East.
“Although it is not known how the virus was introduced to the U.S., it may have entered this country in an infected traveler, bird or mosquito,” IDPH reported.
The first case in Illinois was reported in 2001 in two dead crows discovered in the Chicago area. By 2002, all but two of Illinois’ 102 counties reported West Nile activity.
People get West Nile disease from the bite of a mosquito (primarily the Culex group of species) that is infected with West Nile virus. A mosquito becomes infected by biting a bird that carries the virus. West Nile virus is not spread by person-to-person contact or directly from birds to people.
What are the symptoms of West Nile virus?
Health officials remind the public that most mosquitoes do not carry West Nile virus, and most people infected do not feel sick.
However, approximately 20% of those infected develop a fever and flu-like symptoms. Furthermore, severe illness may occur in approximately one in 150 people, and is most likely to impact those over age 55 and those with compromised immune systems.
According to IDPH, symptoms generally begin between three and 15 days after a bite from an infected mosquito. They range from a slight fever, headache, rash, swollen nodes and conjunctivitis (irritation of the eye) to the rapid onset of a severe headache, high fever, stiff neck, disorientation, muscle weakness, coma or death.
People don’t need to rush to a doctor just because they’ve been bitten, officials said, noting that infections from bites are “rare.” They do encourage anyone who develops symptoms after a bite to seek medical attention, however.
“Patients with mild symptoms are likely to recover completely and do not require any specific medication or laboratory testing,” according to IDPH.
How can you prevent the virus?
Health officials advise taking the following steps:
- Using EPA-registered insect repellent according to label instructions, especially when applying to children.
- Wearing long-sleeved shirts and pants when outside between dusk and dawn.
- Controlling mosquitoes indoors by making sure that window and door screens do not have holes and by using air conditioning if possible.
- Controlling mosquitoes outdoors by keeping grass and weeds short to eliminate hiding places for mosquitoes and emptying items that hold water like flowerpots or birdbaths once weekly.
- Checking on neighbors regularly, especially those who are older, live alone or need additional assistance.
(Except for the headline, this story has not been edited by PostX News and is published from a syndicated feed.)
