What you need to know about equine vaccinations

Farm Forum

Vaccination of horses has become a hot topic among equine veterinarians and owners. There is not one vaccination program that is appropriate for every horse, every time. The horse’s immune system is not the same as ours. Therefore, we vaccinate yearly and sometimes more often, as discussed below.

Of course our primary interest is focused on what is best for our patients as far as balancing benefits and risks of vaccination. For the large majority of our patients, side-effects from vaccination are very rare. We are able to give all “spring” shots on one day with little to no negative effects reported.

The following guidelines have been developed through years of experience, as well as through information and consensus reported from the American Association of Equine Practitioners (AAEP). The vaccines will be listed starting from what we consider “core” vaccines to what we see as more “elective” vaccines. These are recommendations for healthy adult horses who have been vaccinated appropriately in the past. If we have a patient with unknown vaccination history, or a new foal or pregnant mare, these guidelines differ significantly. We will coordinate a specific program for your individual horse based on their age, overall health, and risk factors.

Equine Vaccination Guideline

1. Rabies:

· Although rabies is infrequent in horses, it is a significant risk to people and is 100% fatal. It is therefore considered a core vaccine.

· Vaccine Schedule: Annual booster.

2. Tetanus:

· Tetanus is a progressive and often fatal disease caused by the bacteria Clostridium tetani, which is ubiquitous in the environment.

· The disease is caused by a neurotoxin that is produced when the bacteria infects wounds (especially puncture wounds and deep lacerations).

· It causes progressive “stiff” paralysis that can be fatal if not treated.

· While the disease is not contagious among horses or people, horses are very sensitive to the neurotoxin and therefore tetanus is considered a core vaccine.

· Vaccine Schedule: Annually or at the time of a wound or surgery.

3. Eastern equine encephalitis/western equine encephalitis (EEE/WEE):

· These are neurologic diseases that cause a range of symptoms in horses and people including fever, lethargy, recumbency, seizures, mental dullness and death.

· They are transmitted by mosquitoes and other blood sucking insects from birds and rodents to horses or humans.

· They are NOT contagious from horse to horse, human to human or horse to human.

· The Northeast is considered endemic for these diseases and there have been deaths in horses in the recent past confirmed caused by EEE.

· The vaccines available are highly efficacious and very safe.

· Vaccine schedule: Annually

4. West Nile virus:

· West Nile Virus causes neurologic disease similar to EEE and WEE

· It is 33% fatal in horse and surviving animals often have long term effects of the disease.

· Over 24,000 cases since 1999 in US horses. The number of new cases per year in horses continues to decrease (probably because we vaccinate so well!)

· The vaccines available are highly efficacious and very safe.

· Vaccine schedule: Annually

· NOTE: EEE/WEE, Tetanus and West Nile Virus is a combined vaccine product that we use regularly.

5. Equine herpes virus (EHV)/rhinopneumonitis:

· Rhino is caused by Equine Herpes Virus (EHV). It is divided in to subtypes EHV-1 and EHV-4.

· It causes a variety of clinical disease, including abortion, weak or stillborn foals, acute neurologic disease and upper respiratory disease. This disease group has been very controversial in the last several years due to neurologic outbreaks.

· It is highly contagious from horse to horse via nasal secretions and can live in the environment for at least 14 days.

· The vaccines do NOT protect against the neurologic form of the disease. However, the vaccines may help reduce spread of the disease from horse to horse.

· Vaccine Schedule: Bi-annually (or more frequently if warranted) Due to the highly contagious nature of the disease, and the fact that the vaccine may not provide long-lived protection.

6. Influenza:

· Influenza causes similar signs to human flu. High fevers, lethargy, nasal discharge, cough.

· Influenza has many strains and sometimes the vaccine doesn’t protect against them all. The vaccine is only protective for 4-6 months.

· It is highly contagious and is most common in horses that travel a lot and are exposed to new horses, or at show grounds, race-tracks, etc.

· Vaccine Schedule: Bi-annually is recommended, or more often if travelling and showing frequently.

· NOTE: Influenza comes in a combination vaccine with Rhino. (Flu/Rhino EHV4-1)

7. Strangles:

· Caused by a bacteria, Streptococcus equi, strangles is characterized by high fever, thick mucopurulent nasal discharge (mucous and pus) and swelling and abscessing of the lymph nodes of the head and upper throat.

· The organism is persistent in the environment and is highly contagious from horse to horse.

· There are two types of vaccines. One is injectable (intramuscularly) and one is intranasal (squirted up the nose). The injectable is easier to administer, but is not as protective as the intranasal.

· Vaccine Schedule: Annually. Recommended for horses that travel, show or live in barns that have horses coming in and out on a regular basis.

8. Potomac horse fever:

· Caused by Neorickettsia risticii (formerly Ehrlichia risticii), this disease has a complex lifecycle, including snails and slugs. It is believed to be transmitted to horses through accidental ingestion of insects (mayflies, caddis flies, aquatic insects) who have ingested the organism in water. It is therefore more common in areas with water, snails, and aquatic insects.

· The disease is seasonal, worse in summer months, and is more common in areas South of Maine. However, recently there have been several suspicious cases in Maine.

· Clinical signs include fever, diarrhea, lethargy, colic, and laminitis. Unfortunately, the disease is often fatal.

· The vaccine has variable efficacy and is not known to have long lasting immunity.

· Vaccine Schedule: Annually, but not commonly vaccinated for due to poor vaccine protection.

Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or