Eastern equine encephalitis is one of the most hazardous mosquito-borne diseases in the U.S., with a 33 percent death rate in people who end up being ill, according to the MDHHS. The department stated the 22 reported cases in horses are twice as many cases as the exact same time last year. More than 25 percent of the nations Eastern equine encephalitis cases last year were detected in Michigan, according to the state.