First mosquitoes to test positive for West Nile Virus in Illinois located in Chicago suburb

The first mosquitoes to test positive for West Nile Virus in Illinois this year have been detected in Roselle, state health officials said Thursday.

The DuPage County Health Department collected a positive batch on Tuesday.

No human cases of the virus have been reported so far this year.

"This is the time of year when West Nile virus make its annual appearance," said IDPH Acting Director Amaal Tokars. "We remind everyone -- and especially older people and those with weakened immune systems -- to take precautions to protect themselves from mosquitoes and the viruses they carry by wearing insect repellent and eliminating standing water around their home where mosquitos breed."

Health officials say they monitor the virus by conducting laboratory tests for mosquito batches, dead crows, blue jays, robins and other perching birds.

Additionally, officials will test sick horses and humans with West Nile virus-like symptoms.  

"People who see a sick or dying crow, blue jay, robin or other perching bird should contact their local health department or check their website for details to determine if the bird will be picked up for testing," health officials said in a statement.

The virus is transmitted through the bite of a Culex pipiens mosquito — also known as a house mosquito — that has picked up the virus by feeding on an infected bird. 


Symptoms include: fever, nausea, headache and muscle aches. 

Health officials say four out of five people infected with West Nile virus will not show any symptoms. 

Though rare, severe illness including meningitis, encephalitis, or even death, can occur. 

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.

Additional information about West Nile virus can be found here.