The year’s first mosquitoes with West Nile virus have been identified, Chicago Department of Public Health announced Friday morning.
At least 16 counties across the state have had cases of West Nile virus in birds, mosquitoes and horses, though no human cases have been reported yet this year.
Cook and McHenry counties have seen the bulk of the infected mosquitoes, with 15 and 11 each.
A batch of mosquitoes in Lake in the Hills tested positive for the virus June 2, making them the first of the 2025 season.
The virus typically spreads through infected mosquitoes, though most mosquitoes do not carry the virus, and 80% of people who get the virus won’t experience the flu-like symptoms that come with it, the city health agency said.
However, one of every 150 people infected will experience severe infections, which are more common in those over age 55 and anyone with a weakened immune system.
“As the weather gets warmer, all Chicago residents are encouraged to Fight the Bite and protect themselves against mosquito bites so they can remain safe and healthy this summer,” Dr. Olusimbo Ige, CDPH commissioner, said in a statement.
The agency recommends that people wear long-sleeve shirts and pants outdoors between dusk and dawn, using EPA-approved insect repellent; keeping grass cut, replacing the water in bird baths and other basins weekly; and ensuring window screens don’t have holes in them to reduce the chances of being infected.
Culex mosquitoes, which are the primary carriers of the virus, typically breed in motionless water with high organic matter, often found in containers like rimless tires, abandoned swimming pools, buckets, bird baths and clogged gutters, health officials said.
To control the potential spread this year, the city has more than 80,000 catch basins citywide to keep the mosquito population at bay and is testing mosquitoes weekly until October. Authorities say the city will apply insecticide where needed.
Last year, Illinois saw nearly 70 human cases of the virus, down from 119 in 2023 and well below the state’s average of about 161 cases per year since 2002. About two dozen people died of the virus statewide last year.
In 2024, suburban Cook County saw 19 West Nile virus cases and five deaths due to the virus — marking the highest number of county deaths due to the disease since 2018, according to Cook County Department of Public Health data.
Contributing: Mohammad Samra