The first three human cases of West Nile virus this season in Chicago were reported Tuesday.

The patients range in age from 40 to 80 years old and live on the Northwest and South Sides. Their symptoms began in late July or early August, the Chicago Department of Public Health said.

Though they are the first cases of the virus reported in Chicago in 2025, three other people have contracted West Nile this year in Illinois, according to the Illinois Department of Public Health. Those cases were reported in DuPage, Lake and downstate Wayne counties.

West Nile virus is typically spread through bites from infected mosquitoes, though most mosquitoes do not carry the virus, health officials said.

About 20% of people infected with the virus will experience a fever and flu-like symptoms. And one

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