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Equine Diseases for Which Vaccinations Exist – Core Vaccines

The risks for certain infectious diseases are common to horses all over North America – and the consequences of these diseases are severe. With that in mind, the American Association of Equine Practitioners (AAEP) has defined four core vaccinations that veterinarians consider basic and essential for all horses. Core vaccines have demonstrated efficacy and safety, giving horses a high level of patient benefit and a low level of risk.

Eastern/Western Equine Encephalomyelitis (EEE/WEE)

These are viral infections transmitted to horses by mosquitoes. They cause severe inflammation of the brain and spinal cord, and most horses with EEE or WEE do not survive. Even those that do can have long-lasting neurological problems. Symptoms can include:

  • severe fatigue,

  • weakness to stand,

  • recumbency,

  • behavioural changes,

  • listlessness,

  • depression,

  • fever (moderate to high),

  • loss or lack of appetite,

  • sensitivity to stimuli (sound, touch),

  • teeth grinding,

  • central nervous system signs, such as:

    • head pressing,

    • dementia,

    • circling, and

    • blindness.

West Nile Virus (WNV)

This is the leading cause of encephalitis (inflammation of the brain) in North American horses. It is a viral infection transmitted to horses by mosquitoes. Some horses infected with WNV may show only mild symptoms; however, in others the disease can be severe and potentially fatal. Symptoms can include:

  • fever,

  • incoordination/ataxia or the loss of control of body movements, particularly of the hind limbs,

  • reduced appetite,

  • muscle tremors, particularly affecting the face, neck, and/or shoulders,

  • depression,

  • overall dullness,

  • head pressing,

  • inability to stand,

  • convulsions, and/or any other signs of neurological disease.


Rabies is a fatal neurological disease that can infect virtually all mammals (including humans). Rabies is usually transmitted in saliva from the bite of an infected (rabid) animal. Bites to horses most often occur around the muzzle, face, or limbs. The transmitted virus migrates to the brain, causing encephalitis (swelling of the brain). Symptoms vary widely, but can include:

  • depression,

  • apparent weakness,

  • muscle tremors and spasms,

  • colic,

  • incoordination,

  • paralysis,

  • lameness, and

  • urinary incontinence.

Rabies is a fatal disease that is preventable by vaccine.


Also known as “lockjaw,” tetanus is an often-fatal disease that occurs when a wound becomes infected with bacterial spores of Clostridium tetani. Some cases of tetanus occur from wounds so small they are not noticed. The spores of the bacteria can be found in soil everywhere. Symptoms can include:

  • Wide-based (saw horse) stance,

  • hyper-reactivity to sound and light,

  • difficulty urinating and defecating,

  • anxiety,

  • muscle rigidity, and

  • inability to walk.

Of all domestic animals, horses are the most susceptible to tetanus. That’s why, of all the core vaccines, tetanus is considered the most basic for all horses.

Tetanus photo from the National Foundation for Infectious Diseases

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