First Mosquitoes with West Nile Found in Joliet
The Will County Health Department’s Environmental Health division announced that mosquitoes collected in Joliet have tested positive for West Nile virus [WNV]. These results represent the first WNV positive mosquitoes identified in Will County this year. Will County residents are reminded to protect themselves from mosquito bites and mosquito-borne diseases.
No human cases of West Nile virus have been reported in Will County so far this year. According to data from the Illinois Department of Public Health (IDPH), WNV has been found in 22 counties in Illinois in 2025. There have been 99 positive batches of mosquitoes in Illinois and one confirmed human case of WNV in southern Illinois.
“With mosquito season underway in Illinois, it is now time for Illinoisans, especially seniors and those with weakened immune systems, to start taking precautions to prevent mosquito bites,” said IDPH Director Dr. Sameer Vohra. “A bite from a mosquito infected with WNV can cause serious illness. The best way to ‘Fight the Bite’ is to practice the ‘Three R’s’: reduce the opportunity for mosquitos to enter your home, repel mosquitos by wearing insect repellent outdoors and report standing water in your community where mosquitoes can breed.”
WNV typically causes mild, flu-like symptoms. According to the Centers for Disease Control and Prevention (CDC), most people [8 out of 10] infected with West Nile virus do not develop any symptoms. About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people who develop symptoms from WNV recover completely, but fatigue and weakness can last for weeks or months.
However, according to the CDC, about 1 in 150 people who are infected develop a severe illness that affects the central nervous system such as inflammation of the brain (encephalitis) or inflammation of the membranes that surround the brain and spinal cord (meningitis). Severe illness can occur in people of any age, however people over 60 years of age are at greater risk for severe illness if they are infected. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.
Because there is no vaccine available to prevent West Nile virus, it is important to avoid mosquito bites.
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, or IR 3535 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. For more information on WNV and what can be done to prevent getting bitten by mosquitoes, visit the Centers for Disease Control and Prevention’s West Nile virus page at https:// www.cdc.gov/westnile/ or at the Illinois Department of Public Health’s West Nile Virus page at https://dph.illinois.gov/topics-services/diseases-and-conditions/west-nile-virus.html