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Vaccinate Horses Against Eastern Equine EncephalomyelitisBy Dr. Bryan Waldridge · July 25, 2011
Eastern equine encephalomyelitis (EEE) is a viral neurologic disease of horses that is spread by mosquitoes. In nature, EEE cycles asymptomatically between wild migratory birds. The mosquitoes that spread EEE prefer to feed on birds rather than mammals. Later in summer, either because water sources begin to dry up or their feeding patterns naturally change, these mosquitoes will feed on mammals such as humans and horses.
Outbreaks of EEE in horses generally precede human cases and usually occur in late summer and early fall. In the United States, the disease typically occurs in the states east of the Mississippi River, but it can also be found farther west.
At least 75-90% of horses with EEE die, and those few horses that survive have permanent neurologic deficits. A common name for EEE is sleeping sickness because affected horses are often profoundly depressed and appear sleepy. Other clinical signs include fever (temperature greater than 101.5°F), inappetence, behavioral changes, and ataxia (unsteady gait). Attempted treatment of EEE is similar as for other equine neurologic diseases, with anti-inflammatory drugs and supportive care.
The American Association of Equine Practitioners recommends inoculation against EEE as a core vaccination for all horses. Horses should be vaccinated against EEE every 6 months. In areas where mosquitoes may be prevalent year-round, more frequent vaccination may be suggested.
Infected horses cannot directly transmit EEE to other horses or humans. The virus is transmitted by mosquito bites only. It is possible during early infections (before the horse shows signs of neurologic disease) that horses can have enough virus in their blood for a mosquito to transmit EEE to other horses or humans. Control of EEE involves regular vaccination and mosquito management.
