Cases of the rare mosquito-borne virus Eastern Equine Encephalitis, known as EEE, are popping up in Michigan and other U.S. states.What is Eastern equine encephalitis (EEE)? EEE virus (EEEV) is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis). EEE cases occur primarily from late spring through early fall, but in subtropical endemic areas (e.g., the Gulf States), rare cases can occur in winter. According to Vector Disease Control International, eastern equine encephalitis virus (EEEV) is a zoonotic alphavirus and arbovirus, and was first recognized in horses in 1831 in Massachusetts. Eastern equine encephalitis virus (EEEV) is maintained in a cycle between Culiseta melanura mosquitoes and avian hosts in freshwater hardwood swamps.