Core Vaccines Every Horse Needs

By Garrett Metcalf, DVM

There are many possible dreadful diseases that horses can contract through various insect vectors, ticks, wildlife and even wounds that are rather easy to prevent with routine core vaccinations. Oklahoma has just about every insect known to man to offer, as all Oklahomans are fully aware of especially in the spring and summer, making it a very good environment for some of these key viruses to spread. The five types of diseases that will be discussed in this article are commonly referred to as the deadly five, and that is why they make the core vaccine list because if one of these diseases is contracted it can be game over for your horse. Before spring arrives, the core vaccines should be on every horse owners to do list as a common health care checklist that should be just as routine as deworming and dental care.

The American Association of Equine Practitioners (AAEP) and American Veterinary Medical Association (AVMA) have established key guidelines for vaccinations for horses that are required based on risk to the public and to the horse themselves. The five diseases listed as core vaccines are Rabies, Tetanus, Eastern equine encephalomyelitis virus, Western equine encephalomyelitis virus and West Nile virus.

The AVMA defines core vaccinations as those “that protect from diseases that are endemic to a region, those with potential public health significance, required by law, virulent/highly infectious, and/or those posing a risk of severe disease. Core vaccines have clearly demonstrated efficacy and safety, and thus exhibit a high enough level of patient benefit and low enough level of risk to justify their use in the majority of patients.”  (AAEP website)

The reason these deadly five diseases are listed as core vaccines is because they pose a possible public health risk, are highly virulent or infectious, have a high mortality rate and can be effectively controlled with routine vaccination with great efficacy. It’s important to remember that vaccines are not 100% effective for every disease but well worth that risk when it comes to protect against these five deadly diseases.

There are many other diseases that horses may or may not need to be protected against with vaccinations. These diseases are listed under “risk based” immunizations depending on travel, environment, geographic circumstances and even competition/racing venue requirements before entering into an event. With recent localized outbreaks of equine herpes virus at race tracks, shows and barrel races, many venues and race tracks require very recent vaccinations for these viruses before permitted onto the grounds. Here is a list of risked based diseases vaccinations are available for: Anthrax, botulism, equine herpes virus 1 & 4, equine viral arteritis, influenza, rotaviral diarrhea and strangles. These diseases and the risk of contracting them must be weighed on an individual horse bases versus the risk of the vaccine itself.

Many vaccines today that are available for horses have all core vaccines in one shot except rabies. One vaccine provider has developed the first all five core diseases in one single vaccine. Horses just like other species require multiple boosters to generate an appropriate immune response to be protective. Unvaccinated horses or horses that don’t have a documented vaccine history it is recommended to have at least one booster four to six weeks after the first dose to get an adequate response and then annually after that. In some endemic areas of the country with higher cases of West Nile and other viral encephalomyelitis diseases due to prolonged mosquito vector season it is often recommended to have a booster in the mid-to-late summer to have added protection against these particular viruses.

Below is a breakdown of each disease and its importance for your horse and even yourself to be protected against.

Rabies –

Highly deadly virus that is unsurvivable for any mammal that contracts the disease and begins to show clinical signs, even for humans. As of 2016 only four people have survived rabies infection after showing clinical signs, so the odds are very poor. One of the most difficult aspects of rabies in horses is the variability of clinical signs. Horses can display two clinical manifestations of the disease: Furious/Mad form or Dumb/Stuporous but really it can look like anything early on. Veterinarians are trained that rabies can display almost as anything and should always be on the list for a horse that presents with neurologic symptoms, especially horses with no vaccine history for rabies. Horses can display colic, ataxia, blindness, hypersalivation, depression, weakness and even lameness. Also there is no ante-mortem test meaning there is no test to confirm rabies until the horse is dead or euthanized and the brain is collected for testing. Rabies is transmitted via bites from infected rabid wildlife such as skunks (highest transmitter in Oklahoma), raccoons, fox and bats.

EEE/WEE –

Eastern and Western equine encephalomyelitis is transmitted like other viral enchephalitides via the mosquito vector. Clinical signs are neurologic signs of ataxia, blindness, head pressing or head tilt, recumbency, seizures and paralysis of the throat/tongue. Only up to 15% of horses survive EEE. WEE has a better survival rate up to 50% and has very similar sign as EEE. Birds are common carriers of EEE/WEE and are the reservoir for these viruses.

West Nile –

A very commonly know virus that is also transmitted by mosquitoes to horses, humans, birds and other mammals. Birds again are the largest reservoir for this virus. The virus affects the central nervous system by creating inflammation around the brain and spinal cord. Symptoms or clinical signs are fever, depression, muscle fasciculations, weakness and ataxia. The severity of the disease is horse dependent and not all horses get the disease but among those horses that do about 1/3 will die from it. Also almost half of horses will have lasting neurologic effects from the disease.

Tetanus –

The causative bacterium was first discovered in 1884 by injecting wound exudates from humans with tetanus into animals leading to the discovery that Clostridium tetani is the causative bacteria. The bacteria is found everywhere in the environment including the soil and manure of horses. Horses are rather sensitive to the neurotoxin produced from Clostridium tetani that leads to the clinical signs of tetanus. The bacteria enter the horse’s body through wounds, cuts or even surgical wounds such as castration sites. The spores of the bacteria turn into the vegetative form when it begins to grow and replicate. The neurotoxin produced from the bacteria enters the central nervous system by peripheral nerves. The clinical signs of tetanus are muscle spasms, stiffness, prolapsed third eyelids, extended head and neck, elevated tail and retracted lips. As the disease progresses, horses will become recumbent and have difficulty breathing. Life saving treatments can be implemented to save the infected horses but still up to 75% of horses will die.

What all these disease have in common besides death is that these deaths are extremely excruciating, painful and miserable. There is no doubt from seeing these cases personally and from watching teaching videos that these horses are suffering enormously. What makes it even more difficult and disheartening when we see these cases is that they are so easily preventable with vaccination. The bottom line is that vaccines can save your horse’s life from these deadly diseases and vaccines are rather inexpensive especially compared to the expensive of trying to treat the horse once they are ill. Please talk to your veterinarian about getting your horse or horses protected with core vaccinations and if any other vaccinations are necessary based on your situation.

Read more great articles in the March 2020 issue of Oklahoma Farm & Ranch.