A rare and deadly mosquito-borne disease that causes brain swelling in humans has been detected in Michigan, and state officials are urging residents to take precautions. Mosquitoes in Bay County tested positive on Monday for Eastern Equine Encephalitis, or EEE, a virus that caused a deadly outbreak in Michigan in 2019. EEE is one of the most dangerous mosquito-borne diseases in the U.S. and has a 33% fatality rate in humans.