Minnesota recently had its first encounter with eastern equine encephalitis (EEE) when the disease was confirmed in two horses in separate areas of the state. One horse was from Blue Earth County in southern Minnesota, and the other was from Kanabec County, in the eastern part of the state. Two other cases are suspected, but tests have not yet confirmed the presence of EEE.

According to Paul Anderson, DVM, Director of the equine division at the Minnesota Board of Animal Health, the two confirmed cases were horses that had not been vaccinated for EEE, although Minnesota horse owners generally have their horses vaccinated for the disease. Anderson said that officials are encouraging horse owners to vaccinate if they haven’t already, but are leaving the decision to booster to horse owners and their practicing veterinarians. The vaccine should be protective for a year.

The first case in Blue Earth County was confirmed in late August, and the Kanabec case was confirmed Sept. 18. “Both deaths were very quick—less than 24 hours from onset of clinical signs,” said Anderson. He explained that the pending cases were two horses that died on the same farm in an area west of the Twin Cities.

Eastern equine encephalitis can be incubated from one to three weeks. Infected horses can show lethargy, ataxia, droopy eyes and lips, fever, inappetence, depression, elevated heart rate, and white blood cell count abnormalities. The disease is spread by the bite of an infected mosquito, and cannot be transmitted from horse to horse