ILLINOIS — The Illinois Department of Public Health (IDPH) is reminding the public that along with the start of summer, mosquito season is getting underway in Illinois and that positive batches of West Nile virus (WNV) have been reported in four counties around the state. The reminder comes as public health officials around the country are highlighting the importance of taking action to “Fight the Bite” during National Mosquito Control Awareness Week, June 18-24.

IDPH supports mosquito control efforts throughout the state by providing a total of $2.5 million in funding to the 97 local health departments in Illinois for vector surveillance and control activities. This includes purchasing and applying larvicide, working with local 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 and also collect sick or dead birds for West Nile virus testing.

While no human cases of West Nile virus have been reported in Illinois so far this year, there were 34 human cases (which are significantly under-reported) and eight deaths attributed to the disease in the state in 2022, the most in any year since 2018, when there were 17 deaths. A total of ten batches of mosquitos that tested positive for West Nile virus have been reported this year in Cook, LaSalle, Morgan and St. Clair counties.

“Diseases such as West Nile virus pose a serious health threat, especially to our seniors or individuals who have weakened immune systems,” said IDPH Director Dr. Sameer Vohra. “We have already identified ten mosquito batches that are positive for West Nile virus, and this underscores why it is important for Illinois residents to protect themselves this summer. Please ‘fight the bite’ by wearing insect repellent while outdoors and eliminating standing water around your homes where mosquitos can easily breed.”

Updates on where cases have been reported can be found on the IDPH West Nile Virus Surveillance page.

The first batch of mosquitos to test positive for WNV this year was reported on May 30 in Evanston. In 2022, the first batch of mosquitoes to test positive were collected on May 24 in DuPage County. Last year, 44 counties in Illinois reported a West Nile virus positive mosquito batch, bird, horse, and /or human case. The youngest person to report a case of West Nile virus in Illinois last year was 26 years old, while the median age of human cases was 64.

Monitoring for West Nile virus in Illinois includes laboratory tests for mosquito batches, dead birds, as well as testing sick horses and humans with West Nile virus-like symptoms.  People who see a sick or dead crow, blue jay, robin or other perching bird should contact their local county or city health department, which will determine if the bird will be picked up for testing.

West Nile virus is transmitted through the bite of a Culex species 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 meningitis or encephalitis, or even death.  People older than 60 and individuals with weakened immune systems are at higher risk for severe illness from West Nile virus.

IDPH encourages 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.

Additional information about West Nile virus can be found on the IDPH website.