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Eastern equine encephalomyelitis (EEE) is a Mosquito borne viral disease of all equine species. EEE is a highly fatal, yet preventable (by vaccination) neurological disease in horses. Horses are the most susceptible animal species to EEE infection and have case fatality rates ranging from 50 percent to 90 percent in animals that exhibit clinical signs. Emus and ostriches are also highly susceptible to infection with EEE, with case-fatality rates up to 85 percent.
The virus that causes EEE is transmitted primarily by mosquitoes that bite an infected animal and then bite and feed on another animal or human. The speed with which the disease spreads depends on the density of mosquito populations. Owners of equines have an essential role in preventing EEE from spreading. Horse owners are encouraged to vaccinate their animals and put safeguards in place that prevent animal exposure to mosquitoes, as well as report any suspicious signs of EEE in animals to a veterinarian.
Clinical SignsEquines infected with EEE may show one or more of the following signs:• Fever• Depression• Loss of appetite• Weakness• Central nervous system disorders (lack of coordination, chewing movements, head pressing,"sawhorse" stance, circling, paddling motion of the limbs, and convulsions)• Irritability and aggressiveness towards handlers• Blindness• Excitability• Abnormal sensitivity to light and soundIn some cases, horses infected with EEE may show no clinical signs before dying.
A local veterinarian is the best source for information regarding Equine disease, vaccination and supportive therapy if your animal has become ill. Additionally, eliminating standing water on your property (rain barrels, bird baths, clogged gutters, pet bowls…) will deprive mosquitoes of a necessary breeding environment and will help to reduce mosquito populations in your area.
EEE probably will never be eradicated from the United States because of the reservoirs that exist in so many areas throughout the country. Therefore, continual vigilance and conscientious immunization programs will always be necessary.
Additional InformationFor more information, contactUSDA, APHIS, Veterinary Services4700 River Road, Unit 41Riverdale, MD 20737–1231Telephone (301) 851-3599Fax (301) 734–7817