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IDPH: West Nile Virus Specimens
Confirmed in 17 Illinois Counties As Mosquito Control Awareness Week
Marks Start of Summer 2025
[June 19, 2025]
SPRINGFIELD – The Illinois
Department of Public Health (IDPH) is reminding the public that
along with the start of summer, mosquito season is underway in
Illinois. With this comes the risk of West Nile virus (WNV), which
has been confirmed from environmental samples in 17 counties around
the state so far this year. 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 15-21.
No human cases of WNV have been reported in Illinois so far this
year, but in 2024, there were 69 confirmed human cases of WNV
including 13 deaths, the highest number since 17 WNV-related human
deaths were recorded in 2018.
“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.”
A county is considered positive for West Nile virus if a mosquito,
horse or human from that county tests positive for the virus. The
counties to report WNV so far this year included Bureau, Christian,
Cook, DeKalb, DuPage, Fulton, Grundy, Hancock, Henry, Marshall,
McDonough, McHenry, Peoria, Scott, Stark, Tazewell and Winnebago.
Last year, WNV was confirmed in 72 counties in Illinois.
The first WNV-positive mosquito batch of this year was found May 9
in Rockford.
Updated data on WNV can be found on the
IDPH West Nile Virus Surveillance page.
IDPH supports mosquito control efforts throughout the state by
providing $2.8 million in funding to Illinois’ 97 local health
departments for vector surveillance and control activities. This
includes purchasing and applying larvicide, working with 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.
Monitoring for WNV in Illinois includes tests for mosquito batches,
as well as testing sick horses and humans with West Nile virus-like
symptoms.
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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 paralysis, meningitis or encephalitis (i.e.
brain and nerve infections), 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.
Click
here for additional information about West Nile virus.
[Illinois Dept. of Public Health]
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