First mosquitoes test positive for West Nile virus in Cook County

The Illinois Department of Public Health confirmed Thursday that three batches of mosquitoes have tested positive for West Nile virus in Cook County.

These are the first mosquitoes to test positive for West Nile virus in Illinois so far this year.

The North Shore Mosquito Abatement District collected a positive batch of mosquitoes in Evanston on May 30 and the Northwest Mosquito Abatement District collected two positive mosquito batches on May 31 in Park Ridge, officials said.

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

"The reports about the first batches of mosquitoes with West Nile virus is a good reminder that this is the time of year when Illinois residents should begin protecting themselves from vector-borne diseases," said IDPH Director Dr. Sameer Vohra. "We urge everyone -- and especially older people and those with weakened immune systems -- to take precautions to protect themselves and their families from mosquitoes and the viruses they carry by wearing insect repellent and eliminating standing water around their home where mosquitoes breed."

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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, health officials said.

In 2022, 44 counties in Illinois reported a West Nile virus-positive mosquito batch, bird, horse, and /or human case. 

There were 34 human cases recorded last year, with eight deaths. However, Illinois health officials say human cases are usually underreported.