Equine Vaccinations & Deworming

Stilwell Animal Hospital & Equine Center, P.A. is dedicated to providing the best preventative care for your horse. Vaccination and deworming protocols are one of the many ways we try to proactively approach preventable diseases in horses. We tailor our vaccination protocols to accommodate the individual needs for your horse, however we have some general guidelines. Some vaccinations are recommended yearly, some bi-yearly and others are recommended based on your horse’s individual risk.

Annual Vaccinations:

  • Sleeping sickness (EEE, WEE)
  • Tetanus
  • Rabies
  • Bi-annual Vaccinations:
  • West Nile Virus
  • Influenza
  • Rhinopneumonitis (EHV-1 & EHV-4)

As-needed vaccinations:

  • Potomac Horse Fever
  • Strangles
A vet giving a horse a vaccination

Pregnant mares are recommended to be vaccinated for Rhinopneumonitis at 5, 7, and 9 months gestation to prevent virally-induced abortion and provide protective immunity for their foal.

Deworming in horses is a hot topic amongst veterinarians and horse owners, and we at Stilwell Animal Hospital & Equine Center, P.A. take a preventative care approach. We like to deworm horses at least on a bi-annual basis with your horse’s regular vaccination visits, and take fecal samples for evaluation. A fecal egg count can provide us with the necessary information to determine if your horse needs to be dewormed more frequently than bi-yearly and with what dewormer. Horses are classified into different “shedding status” categories, which is a qualitative analysis of how many worm eggs are “shed” in the feces based on the fecal egg count. If a horse has high numbers of eggs in their fecal sample, they are considered a “high shedder” and need to be dewormed more frequently such as every 8 weeks. If a horse has very few eggs in the feces, then they are considered a “low shedder” and only need their bi-yearly deworming. We are happy to discuss with each client what their horse’s shedding status means for their individual deworming protocol.

A vet giving a horse a vaccination


What is “sleeping sickness”?

Eastern and western encephalomyelitis is colloquially referred to as sleeping sickness, and is a viral infection that affects the central nervous system. This virus is endemic mainly in wild birds, which do not show symptoms of disease, and is transmitted by biting insects like mosquitoes. Clinical signs of disease start as mild as transient fever and depression, but can progress to neurologic signs like aggression, blindness, head pressing, circling, head tilt, and paralysis of mouth and tongue. Death occurs in 75-80% of horses that progress to neurologic symptoms, and those that are not fatal do not make complete recovery. There is no cure for viral encephalomyelitis, and treatment is supportive care based on symptoms. Prevention is the best treatment, and so horses should be vaccinated annually and mosquito populations kept to a minimum.

Why does my horse need vaccinated for tetanus yearly when people are protected for years from a single vaccine?

Tetanus is a neuromuscular disease caused by toxins produced by the bacteria Clostridium tetani, which are found in the soil and intestinal tract of people and animals. Horses are especially sensitive to the toxins produced compared to humans and other animals, and are also more likely to acquire the types of wounds that permit growth of clostridium and release of toxins. In the soil, these bacteria are present as spores that when introduced to an oxygen-deprived environment (such as puncture wounds, fractures, castration incisions, and foaling injuries) start growing and producing toxins. We also recommend that a tetanus vaccine be given prior to castration (gelding) to prevent the bacteria from responding to the surgical site.

Why does my horse need vaccinated for Rabies?

All mammals are susceptible for infection with rabies including humans, and it is a rapidly fatal incurable disease. Horses are often exposed to wildlife that are known to carry rabies (raccoons, skunks, and bats are most common), and so are more at-risk for infection. The most important reason for vaccinating horses for rabies is for the health and safety of the people handling them. Rabies in horses often shows signs similar to other viral diseases, and so diagnosis may happen after humans have been inadvertently exposed to the virus. We recommend yearly vaccination for rabies for the health of both you and your horse.

What is Rhinopneumonitis, and why does my mare need vaccinated for it during gestation?

Equine herpesvirus 1 (EHV-1) and 4 (EHV-4) are the viruses responsible for rhinopneumonitis in horses, which causes upper respiratory disease on first exposure. The EHV-4 strain is primarily respiratory, but EHV-1 can cause abortions and neurologic signs in addition to respiratory. In pregnant mares, we worry especially about the EHV-1 strain because of its propensity to cause late-term abortions or birth of fatally-ill foals. Like other herpesviruses, EHV-1 and EHV-4 can infect previously exposed animals without causing obvious disease. Then, under stressful conditions (such as pregnancy) the latent virus can become active and cause disease. Often the respiratory signs are so mild in pregnant mares that they go unnoticed, and the first sign of infection is compromise of the foal.

Why does my horse need vaccinated for equine influenza?

Equine influenza is highly contagious and the virus spreads rapidly through groups of horses in aerosolized droplets dispersed by coughing. The severity of signs depends on the degree of existing immunity, among other factors. We recommend vaccinating horses twice a year to keep their immune system prepared and prevent outbreaks. Horses especially at risk are horses traveling to shows or events where horses come together from various geographic locations.

How do I know if my horse should be vaccinated for Potomac Horse Fever?

Potomac horse fever is also known as equine monocytic ehrlichiosis, and is caused by the organism Neorickettsia risticii. This organism is an intracellular bacteria that is commonly found in snails, slugs and certain insects that are near water and is most prevalent in late summer and early fall. This organism can cause fever, diarrhea and lethargy, possibly leading to mild colic and laminitis. The vaccination for Potomac horse fever is recommended for horses that have access to water (ponds, lakes, streams etc) during late summer and early fall, and should be administered during specific times of year to lessen severity of clinical signs if exposed.

What is “strangles” and how do I know if my horse should be vaccinated for it?

Streptococcus equi subspecies equi (S. equi var. equi) is the bacterium which causes the highly contagious disease strangles. Strangles commonly affects young horses (weanlings and yearlings), but horses of any age can be infected. Vaccination against S. equi is recommended on premises where strangles is a persistent endemic problem or for horses that are expected to be at high risk of exposure. Following natural infection, a carrier state of variable duration may develop and intermittent shedding may occur, putting surrounding horses at risk. The organism is transmitted by direct contact with infected horses or sub-clinical shedders, or indirectly by contact with: water troughs, hoses, feed bunks, pastures, stalls, trailers, tack, grooming equipment, attendants’ hands and clothing, or insects contaminated with nasal discharge or with pus draining from lymph nodes of infected horses. Due to the severe contagiousness of the disease, outbreaks are common and usually affect an entire barn or herd if affected horses are not well-quarantined.