HappyHorseShots

Across the United States, veterinarians receive regular reports from various departments of livestock. According to the Montana Department of Livestock (MDOL) dated April 30, 2014, Montana had the third highest confirmed case count of West Nile Virus in the United States. Equine herpes virus is a repeat offender in horse populations as well, also making the Department of Livestock bulletins as well. But with all of the different diseases out there, how do you know which vaccinations your horse should have and when?

Veterinarians generally refer to two types of equine vaccinations: core vaccinations and risk-based vaccinations. Core vaccinations are for diseases that either exist in the area, have the potential of causing serious disease or killing your horse, or are public health issues. Risk-based vaccinations help prevent diseases that will make your horse sick, but they are less likely to cause serious disease or kill the horse.

Core Vaccinations

This table lists core equine vaccinations that most veterinarians would suggest giving as part of a regular vaccination program.

Disease Alternate Names Presentation Mortality Rates
  • Eastern Equine Encephalomyelitis (EEE)
  • Western Equine Encephalomyelitis (WEE)
 

  • Triple E
  • Sleeping sickness
Nervous signs appear during fever, including sensitivity to sound, periods of excitement, and restlessness. Brain lesions appear, causing drowsiness, drooping ears, circling, aimless wandering, head pressing, inability to swallow, and abnormal gait. Paralysis follows, causing the horse to have difficulty raising its head. The horse usually suffers complete paralysis and death 2–4 days after symptoms appear. The presence of an infected horse in the area indicates that mosquitoes carrying EEE, WEE, or VEE are present. Those insects pose a threat to both humans and horses. However, humans cannot become infected with EEE, WEE, or VEE by handling an infected horse, nor can a horse acquire the virus from another infected horse.For a more thorough briefing on encephalomyelitis, read this fact sheet. 70–90% and higher
West Nile Virus (WNV)   Symptoms of infection include fever, weakness or paralysis of hind limbs, and general ataxia (weakness). The horse’s vision becomes impaired, and it exhibits head pressing, aimless wandering or walking in circles, head pressing, an inability to swallow, and an abnormal gait. The horse will also appear as hyperexcitable before lapsing into a coma.The presence of an infected horse in the area indicates that mosquitoes carrying WNV are present. Those insects pose a threat to both humans and horses. However, humans cannot become infected with WNV by handling an infected horse, nor can a horse acquire the virus from another infected horse. 30% and higher
Tetanus Lockjaw Within 24 hours of infection, the horse begins to exhibit initial signs, including a generalized spastic activity of the large muscles required for standing; the legs are extended tightly in a rigid fashion, and the horses are said to adopt a “sawhorse” stance. In addition, the retraction of the eyeball itself into the socket and spasms–often referred to as “flashing”–of the third eyelid over the eye can occur. All of the muscle spasms can be evoked by sudden sound, movement, or touch. These horses can become recumbent and often will lie on their sides with their legs extended in rigid extension and their neck extended in an upward manner.Tetanus symptoms are caused by exotoxins that are actively secreted by the organism, so horses are not actively infected as we commonly think. Puncture wounds are the most likely cause of affected horses, and horses are considered to be very susceptible to tetanus. For a good description of tetanus in horses, read Shoot ‘Em Up, or Why Your Horse Needs a Tetanus Shot Every Single Year. 50% and higher
Rabies   There are three phases of rabies infection: prodomal, furious, and paralytic.

  • During the prodomal stage, symptoms may include fever, loss of appetite, chewing or biting at the infection site, and subtle behavioral changes.
  • During the furious phase (which may not be exhibited by all horses), symptoms may include attempts to eat anything, dilated pupils, disorientation, episodes of aggression, roaming, restlessness, seizures, trembling, and muscle incoordination.
  • During the third and final paralytic phase, a horse may exhibit an inability to swallow, drooling, foaming of saliva, and paralysis of the jaw, throat, and chewing muscles. Paralysis then spreads to other parts of the body, the animal becomes depressed, rapidly enters a coma and dies.

It should be noted that humans can become infected with rabies by handling a rabid horse. For film and literary depictions of dogs infected with the rabies virus, watch “Old Yeller” or read Too Kill a Mockingbird.

100%

Risk-Based Vaccinations

This table lists risk-based equine vaccinations that many veterinarians might suggest giving as part of a regular vaccination program, depending on the horse and its usage.
  • Triple E
  • Sleeping sickness
Disease Alternate Names Description
Distemper Strangles Distemper is a contagious upper respiratory tract infection of horses caused by the bacterium, Streptococcus equi var equi. The disease is spread when the nasal discharge or material from the draining abscess contaminates pastures, barns, feed troughs, stables, and so on. Horses of any age may contract the disease, although younger and older horses are generally more susceptible.
Equine Viral Arteritis (EVA)   Equine Viral Arteritis (EVA) is caused by an RNA virus of the genus Arterivirus. It has been more common in some breeds of horses in the United States, but there is no breed “immunity”. In both the United States and the United Kingdom, it is a notifiable disease, meaning that the veterinarian must report its occurrence to the Department of Livestock.
Equine Influenza Flu Equine influenza occurs globally, and is caused by two main strains of virus: equine-1 (H7N7) and equine-2 (H3N8). The disease has a nearly 100% infection rate in an unvaccinated horse population with no prior exposure to the virus.

Equine influenza is characterized by a very high rate of transmission among horses, and has a relatively short incubation time of one to five days. Infected horse may run a fever, have a dry, hacking cough, have a runny nose, and become depressed and reluctant to eat or drink for several days. However, they usually recover in two to three weeks.

Rhinopneumonitis Equine herpes virus
  • Rhino
  • EHV-4
  • EHV-1 or
    neurologic EHV-1
Equine herpesvirus is relatively well-known amongst horse owners as it can cause abortions in mares, early neonatal death in foals, and respiratory disease in young horses. It can also sporadically cause myeloencephalopathy, a kind of neurologic disease, with hind-limb weakness, decreased tail and anal tone, and urinary incontinence as the most common neurologic symptoms. There are two forms of the virus that are of interest to horse owners: EHV-4 and EHV-1.

  • Equine herpesvirus 4 is a virus of the family Herpesviridae that cause rhinopneumonitis in horses. It is the most important viral cause of respiratory infection in foals. Symptoms include fever, loss of appetite, and a discharge (“snots”) from the horse’s nose.
  • The neurologic form of equine herpesvirus, or neurologic EHV-1, While there is no vaccine for EHV-1, vaccinating for EHV-4 decreases viral shedding for horses that do contract the virus. For more information, read Neurologic EHV-1.
Potomac Horse Fever (PHF)
  • Shasta River Crud
  • Equine Monocytic Ehrlichiosis
Potomac Horse Fever is a potentially fatal febrile illness that is caused by the intracellular bacterium Neorickettsia risticii. Currently, it has been documented in more than 40 states and Canada. (Doc Randall wanted to insert the joke that while horses can get Potomac Horse Fever, politicians regularly get Potomac Fever. I decided to let him.)
Botulism   Botulism is a rare and potentially fatal paralytic illness caused by a toxin produced by the bacteria Clostridium botulinum. The muscle paralysis is progressive, usually beginning at the hindquarters and gradually moving to the front limbs, neck, and head. Death generally occurs 24 to 72 hours after initial symptoms and results from respiratory paralysis. 
Rotavirus  Rota Rotavirus infects the young of many species of animals and is a major cause of diarrhea in wild and reared animals worldwide.
Venezualan Equine Encephalomyelitis (VEE) VEE symptoms are similar to those off EEE and WEE. For a more thorough briefing on eastern, western, and Venezualan encephalomyelitis, read this fact sheet.

Determining Your Horse’s Vaccination Program

When determining your horse’s vaccination program, you and your veterinarian will need to consider these factors:
  • How old is the horse?
  • What part of the world your horse lives in?
  • Will the horse be traveling?
  • Will the horse be used for breeding purposes?
  • Is your horse a performance horse, being used regularly for showing, rodeos, or competitions?
Cost can also be a factor–but not the primary driver–in determining a vaccination program.

Additional Reading

The American Association of Equine Practitioners has posted excellent guidelines and charts regarding core vaccination and risk-based vaccination programs.