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Equine Encephalomyelitis Overview

Diagnosing horse ailments requires a vet. (Click here for a list of Florida veterinarians by county)

Equine Encephalomyelitis, a potentially fatal mosquito-borne viral disease that infects horses and humans; also known as equine encephalitis may be caused by several viruses:

  1. Eastern equine encephalitis virus
  2. Western equine encephalitis virus
  3. Venezuelan equine encephalitis virus


Eastern Equine Encephalitis Virus:
Eastern equine encephalomyelitis virus (EEE), commonly called sleeping sickness or "Triple E", is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts, USA in 1831 when 75 horses died of encephalitic illness. Epizootics in horses have continued to occur regularly in the United States. EEE is found today in the eastern part of the country and is often associated with coastal plains.
Western Equine Encephalitis Virus:
The Western equine encephalitis virus is the causative agent of relatively uncommon viral disease Western equine encephalitis (WEE). An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus (arthropod-borne virus) transmitted by mosquitoes of the genera Culex and Culiseta.[1] There have been under 700 confirmed cases in the U.S. since 1964.
In the U.S. WEE is seen primarily in states west of the Mississippi River. The disease is also seen in countries of South America. WEE is commonly a subclinical infection; symptomatic infections are uncommon. However, the disease can cause serious sequellae in infants and children. Unlike Eastern equine encephalitis, the overall mortality of WEE is low (approximately 4%) and is associated mostly with infection in the elderly. There is no vaccine for WEE and there are no licensed therapeutic drugs in the U.S. for this infection.
Venezuelan Equine Encephalitis Virus:
Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis (VEE). VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may suddenly die or show progressive central nervous system disorders. Humans also can contract this disease. Healthy adults who become infected by the virus may experience flu-like symptoms, such as high fevers and headaches. People with weakened immune systems and the young and the elderly can become severely ill or die from this disease