Rocky Valley Veterinary Service

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Eastern and Western Equine Encephalitis

Eastern Equine Encephalitis

• Cause: EEE is caused by the Eastern equine encephalitis virus (EEEV), which belongs to the genus Alphavirus, family Togaviridae. It is primarily transmitted by mosquitoes, with birds serving as the main reservoir hosts.

• Geographical Distribution: EEE is commonly found in the eastern United States, particularly in the Atlantic and Gulf Coast states, but cases have been reported in other regions as well.

• Symptoms: In horses, EEE can cause fever, depression, ataxia (loss of coordination), muscle twitching, and seizures. The mortality rate in horses can be as high as 90%. In humans, EEE can cause flu-like symptoms, encephalitis (inflammation of the brain), and in severe cases, neurological complications, and death.

• Prevention: Vaccination is the primary method of prevention for horses. Mosquito control measures can also help reduce the risk of transmission to both horses and humans.

Western Equine Encephalitis

Cause: WEE is caused by the Western equine encephalitis virus (WEEV), also belonging to the genus Alphavirus, family Togaviridae. Like EEE, it is primarily transmitted by mosquitoes.

• Geographical Distribution: WEE is found in the western United States and Canada, particularly in rural areas.

• Symptoms: In horses, WEE causes similar clinical signs to EEE, including fever, lethargy, weakness, and neurological symptoms. Mortality rates in horses can range from 20% to 50%. In humans, symptoms can range from mild flu-like illness to severe encephalitis, although human cases are less common than with EEE.

• Prevention: Vaccination is also the main method of prevention for horses against WEE. Mosquito control is crucial for reducing the risk of transmission to both horses and humans.

Both Eastern Equine Encephalitis and Western Equine Encephalitis pose significant health risks to horses and humans alike. Vaccination, along with mosquito control measures, remains essential for mitigating the spread of these diseases and reducing their impact on both animal and human populations. Early detection and prompt treatment of cases are also crucial for improving outcomes, particularly in severe cases of encephalitis.