West Nile virus found in mosquitos and birds in 13 Illinois counties, including LaSalle County

CHICAGO – The Illinois Department of Public Health (IDPH) is reminding the public that along with the start of summer, mosquito season is underway in Illinois and with that comes the risk of West Nile virus (WNV), which has been reported in 13 counties around the state so far.

While no human cases of West Nile virus have been reported in Illinois this year, there were 119 human cases reported in 2023, up from 34 human cases in 2022. There were six human deaths attributed to West Nile virus in 2023, compared to seven in 2022.

“West Nile Virus can lead to serious illness, especially for our Illinois seniors and people with weakened immune systems,” said IDPH Director Dr. Sameer Vohra. “With the virus appearing earlier this year following a milder winter and spring, I urge everyone to fight the bite in their communities. Please reduce exposures, wear insect repellent while outdoors, and report any standing water around your community where mosquitoes can breed.”

A county is considered positive for West Nile virus if a bird, mosquito, horse or human from that county tests positive for the virus. To date this year, Illinois has had 11 positive mosquito pools and 10 positive birds from 13 counties, including Champaign, Cook, Douglas, Fulton, Kane, Hancock, LaSalle, Morgan, Washington, Whiteside, Williamson, Winnebago, and Woodford. The first mosquito batches this year were found in mid-May, about two weeks earlier than in a typical year.

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

IDPH supports mosquito control efforts throughout the state by providing a total of $2.8 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.

Monitoring for West Nile virus in Illinois includes laboratory tests for mosquito batches and 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 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 those with weakened immune systems are at highest risk for severe illness.

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.

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