The Michigan Department of Agriculture and Rural Development (MDARD) reported Oct. 11 that the state’s Upper Peninsula has confirmed its first two cases of a mosquito-transmitted equine disease this year.

In a statement on its Facebook page, the MDARD said two horses from different farms in Marquette County tested positive for Eastern equine encephalitis (EEE). Both horses—a 25-year-old Quarter Horse gelding and a 11-year-old Quarter Horse gelding—were unvaccinated and have been euthanized.

“These horses bring the total number of reported cases of EEE in Michigan for 2017 to six: two from Marquette County, two from Clare County, one from Roscommon County, and one from Wexford County,” the MDARD said.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Clinical signs of EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems