Eastern & Western Encephalitis (EEE/WEE)


AAEP Core Vaccination


EEE and WEE are viral infections of the horse’s brain and spinal cord. The virus is maintained in reservoirs (primarily birds and rodents) and transmitted to the host by the bite of an infected mosquito.

Clinical Signs can include:

  • Behavioral Changes
  • Loss of Appetite and fever

These can progress in 12 to 24 hours to:

  • Dementia with head-pressing
  • Teeth-grinding
  • Circling
  • Blindness
  • Ataxia (incoordination)

This disease is fatal in 50-90% of cases.  Surviving horses often have residual mental dullness.  Treatment is generally supportive because antibiotics are ineffective.

There are 2 types of EE commonly seen in North America: EEE and WEE.  A third type, Venezuelan (VEE), is seen in Central America and northern South America but has not been reported in the United States since 1971.

Other AAEP Core Vaccinations: