Eastern Equine Encephalitis
/ Western Equine Encephalitis
spring and summer approach, it is time to think about
preventative vaccinations for horses.
Included in the core vaccinations recommended by the
American Association of Equine Practitioners are Eastern
Equine Encephalitis (EEE), Western Equine Encephalitis (WEE),
and Tetanus Toxoid.
encephalitis viruses are alpha viruses and are spread to
horses by mosquitoes from wild birds and rodents.
Humans are also susceptible to these viruses, although
they are not likely to contract them from contact with horses.
Both viruses are known to occur in North America, with
EEE being more prevalent east of the
and WEE west of the
Equine Encephalitis (VEE) occurs in South America and is
considered a reportable foreign animal disease in the
. There is some
evidence the EEE/WEE vaccines provide cross protection against
and WEE are serious and frequently fatal in the horse.
Symptoms include fever, depression and neurologic signs
which can include altered mentation and vision, wandering,
head pressing, circling, ataxia (stumbling) leading to
paresis, paralysis, convulsions and often death.
Horses that become recumbent generally have a poor
prognosis. Those that
recover often have residual effects.2
and WEE vaccines contain inactivated virus with adjuvant, to
stimulate immune response, and preservatives.
These vaccines have demonstrated to be effective in
protecting against EEE and WEE infection.
Horses should be vaccinated in the spring, prior to
mosquito season to provide the best protection when
transmission is likely. In
areas where the virus is endemic and the mosquito season can
be year round (
), vaccination in the fall may also be recommended by your
unvaccinated horses should receive one dose followed by a
booster in three weeks. They
should be revaccinated yearly (or twice yearly) and also in
outbreak situations when exposure is likely.
and WEE vaccines are often available in combination with other
recommended core vaccines such as Tetanus Toxoid.
Colorado Serum has both EEE/WEE
combination and an EEE/WEE/Tetanus
combination available for horses.
Association of Equine Practitioners, www.AAEP.org,
Eastern/Western Equine Encephalomyelitis, Copyright AAEP 2008
Merck Veterinary Manual Ninth Edition, pages 1027-1031, Merck
and Company, Inc.,