Encephalitis is inflammation of the brain. Encephalomyelitis is inflammation of the brain and spinal cord. A number of different types of viral encephalitis/encephalomyelitis can occur in horses, including among others: Eastern, Western and Venezuelan Equine Encecphalomyelitis (EEE, WEE, and VEE, respectively).
These infections are transmitted to horses by infected mosquitos. The reservoir of the disease in the wild is birds. A mosquito bites an infected bird, takes in the virus, and then bites a horse and transmits the virus.
It is difficult to differentiate between the encephalitis types and West Nile Encephalomyelitis (without an antibody titer) because they all cause similar signs of disease. Symptoms include fever, depression and signs of neurologic disease (wobbliness, weakness), among many others.
EEE, WEE and VEE are reportable diseases in the USA, meaning that if a horse has or is suspected of having either of these disease, vets are required to report it to agricultural authorities (usually the State Veterinarian). These authorities may investigate the case as part of a larger effort to monitor equine health and coordinate with other states and the USDA APHIS in preventing the spread of illness or disease on a national and international level.
Viral encephalitis are all zoonotic. Infected horses cannot directly pass these diseases to other horses, animals or humans. EEE and WEE can be transmitted from infected birds to humans via mosquitos. VEE is the only one of these that can be transmitted from infected horses to humans via mosquitos. Because of this, if you have been exposed to a horse with (or suspected of having) EEE, WEE or VEE you should always contact your doctor. Infection by these viruses can cause life-threatening disease in humans.
Diagnosis is through blood antibody testing.
Treatment is primarily anti-inflammatories and supportive care.
Other Diagnoses Considered
Treatments May Include
Prognosis & Relevant Factors
The prognosis is poor for horses infected with EEE, as it has a very high fatality rate. The prognosis is better but still guarded for horses infected with WEE.
Horses that recover from these diseases tend to have a high incidence of residual neurologic deficits, including general dullness.
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QUESTIONS TO ASK MY VET
Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health