Birds carrying the West Nile virus have been found in Lake, McHenry and DeKalb counties. An Illinois Department of Public Health spokesperson says that brings the number to 13 counties, up from 11 at this point last year. The virus is transmitted by mosquitoes.

Paul Geery works with the Des Plaines Valley Mosquito Abatement District in western Cook County and says it’s too soon to know how the summer’s mosquito population will develop.

“It’s very, very difficult to predict any distance into the future because it really depends on temperature and rainfall, which of course are impossible to predict. At this point, it’s kind of shaping up like a typical season,” he says.

Geery says crews will treat all standing water sites and street gutter drains in the district, hoping to reduce the mosquito population.