(AREA) -- Authorities in Michigan say an insect-spread deer disease has spread to at least 24 counties. The Michigan Department of Natural Resources and Michigan State University announced new figures Monday on confirmed cases of the illness. It's called EHD and is untreatable. The virus causes extensive internal bleeding and is transmitted by a type of biting fly called a midge. The disease is on the rise nationwide because of hot, dry weather. The DNR and Michigan State say they've confirmed 4,217 deer deaths in 24 counties. They say they expect that farmers harvesting crops and hunters taking to the field will find more dead deer. No cases of EHD have been detected in the Thumb-Sanilac, Huron, St. Clair, Tuscola, and Lapeer counties; however, one case was found in Saginaw County this month.