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Eastern/Western Encephalomyelitis

Eastern and Western Equine Encephalitis viruses are transmitted from birds to horses by mosquitoes and other blood sucking insects. Humans are also susceptible to these viruses, although we are unlikely to get it from an infected horse. The virus causes severe inflammation of the brain (encephalitis). Leading to symptoms can include impaired vision, muscle twitches, circling or head pressing behaviors, the inability to swallow, and paralysis. Horses infected with EEE often do not survive.


Tetanus is caused by a type of bacteria which is found in the soil and the environment. Horses are especially vulnerable to the disease as they have no natural immunity and they have a high chance of exposure through wound contamination. The size of the wound is not an indicator of the risk of Tetanus and the disease is typically fatal. Symptoms include protrusion of the 3rd eyelid, a sawhorse stance, sensitivity to stimulus, colic, muscle spasms, labored breathing and death.


Rabies virus is a problem for horses too. It is spread through saliva of an infected animal, typically through a bite wound. Horses are at risk from wildlife and the bite wound may either not be visible or not readily be identifiable. Rabies is a fatal disease with no cure. Symptoms can be difficult to interpret and include colic, lethargy/depression, self mutilation, aggression or present as a down horse that is unable to rise. Rabies is a human health risk and infected horses can potentially transmit the virus through their saliva but there are reports of people being killed as infected horses can be uncontrollably/unpredictably aggressive.

West Nile

West Nile Virus is transmitted by mosquitoes that have fed on infected birds. Mosquitoes can also transmit the virus to humans. It causes a potentially fatal inflammation of the brain and spinal cord/encephalomyelitis. Symptoms include hypersensitivity to touch or sound, muscle tremors/twitching, and other neurological problems including incoordination, ataxia and an inability to stand. Horses can often recover with supportive care but can have persistent symptoms.

Potomac Horse Fever

Potomac Horse Fever is a bacterial disease that causes and enterocolitis (inflammation of the intestinal tract). The disease is often associated with creeks or streams and the bacteria is found in Caddisflies, Mayflies and in freshwater snails. Horses are probably infected by ingesting the bacteria. Infected horses have fevers, colic, diarrhea and laminitis. These symptoms can be mild to severe and can lead to death/euthanasia.


Lyme disease is the most prevalent tick-borne disease in humans and animals in the United States. Symptoms can include fever, stiffness, muscle pain, swollen joints, lameness and it can even cause inflammation of the eyes. Lyme can be difficult to diagnose and expensive to treat. There is currently no vaccine labeled for horses but there are multiple vaccines available for dogs and they seem to be effective in preventing infection or at least helping to lessen the severity of disease.


Influenza or flu is a respiratory virus. It can cause high fever, clear nasal discharge, clear drainage from the eyes, and cough. Just like with humans, the virus is transmitted through coughing/sneezing or contact with contaminated buckets, troughs, etc. Horses tend to recover but Influenza can lead to loss of performance and even heart problems.


Rhino (Rhinopneumonitis) is caused by a herpes virus. There are multiple types of equine herpes virus. Symptoms can range from high fever, clear nasal discharge, cough, lethargy, inappetence, enlarged lymph nodes and swollen legs. Pregnant mares are at risk of miscarriage. Infection is spread through coughing/sneezing and contact with contaminated buckets etc. Horses can become carriers of the virus and can shed the virus without showing symptoms. Occasional Equine Herpes Virus type 1 can cause neurological disease and lead to death/euthanasia. Equine Herpes Viruses can cause outbreaks involving multiple horses and often involve quarantines to limit the spread of the disease.


Botulism is caused by a bacterial toxin. The bacteria are often found in the soil and can be found in fermenting feed or decomposing animal carcasses. Horses can be infected by ingesting the bacteria or through a contaminated wound. Botulism causes a flaccid paralysis of muscles and symptoms can range from difficulty swallowing to an inability to swallow, weakness, inability to stand and paralysis of the respiratory system. The severity of symptoms is related to the amount of toxin the horse was exposed to. Treatment can be very expensive and horses who are severely infected may not recover.


Strangles is a bacterial disease. Infected horses typically have fevers, swollen lymph nodes, and nasal discharge. The bacteria is spread by contact with the nasal secretions either through coughing or through contact with contaminated equipment. Strangles can cause outbreaks and affect multiple horses. It often results in a quarantine of the property until weeks after horses have recovered. Horses can become carriers and while they, themselves, do not show symptoms they can be a source of infection for other horses.

When we vaccinate your horse, we take into account your horse’s age, environment, and frequency of travel. “Core” vaccines are those we strongly recommend to all horses, due to the severity of the disease and risk to public health. Here is a list of what we consider core vaccinations:

  • Eastern & Western Encephalomyelitis (once per year)
  • West Nile Virus (twice per year)
  • Rabies (once per year)
  • Tetanus (once per year)
  • Potomac Horse Fever (twice per year)

Whether we give additional vaccines depends upon your individual horse’s risk factors for contracting these diseases. These vaccines include Flu (Influenza), Rhino (Rhinopneumonitis), Botulism, Lyme, and Strep (Strangles). Read more here

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