Author: Sallie S. Hyman, VMD, DACVIM, CVA
Time for seasonal vaccinations. As horse owners you diligently make an appointment with the vet to come out to vaccinate your horses as scheduled. Vaccination is an immensely important part of maintaining your horse’s health. The advent of vaccination has decreased the mortality and morbidity of many diseases that used to claim thousands of equine lives. And although every horse should be vaccinated, a one size fits all vaccination program is no longer warranted. What your horse receives should be based on sound medical advice from your veterinarian.
Exactly what is a vaccine and how does it work?
The word “vaccine” is derived from the Latin, vaccinus, which means “of a cow.” Edward Jenner produced the vaccine against small pox by using cow pox virus, hence the use of the term.
When the body encounters a foreign substance, called an antigen, the immune system goes on alert. White blood cells called T and B lymphoctes produce antibodies. These antibodies will interact with specific antigens and form an antigen/antibody complex. Other cells of the immune system then target these complexes for destruction and remove them from the body, thus preventing disease. When we vaccinate, we are introducing antigen into the body in order to stimulate the body to produce antibodies against whatever disease for which we want protection. Vaccines do not produce a large scale antibody response that might make us or a horse feel sick, but just enough to get the right antibodies. The most important part of the immune response that takes place, however, is the development of the memory cells for that particular antigen. If the body ever encounters that antigen again, it will mount a swift and exuberant response because of those memory cells. This quick response will help to prevent or lessen the severity of the disease encountered.
What different types of vaccines are there?
There are now several types of vaccines on the market that are designed to stimulate the immune response. Each has it pros and cons, so it is important to discuss with your veterinarian which type is best for your horse. The most widely used types used today are:
Modified Live- made from the disease causing agent that has been made less virulent. The agent can replicate and shedding of active agent is a small concern.
Killed-made from the killed agent. The agent cannot replicate or be transmitted. Adjuvants (components that amplify and modulate the immune response) are necessary to make the vaccine work. Adjuvants have been implicated in some vaccine reactions.
Recombinant-made from antigenic pieces of a pathogen that is combined into a harmless carrier.
How effective are vaccines?
It must be remembered that vaccination is not 100% protective. It is one part of an overall health management program. When considering vaccination, keep in mind the risk of exposure, the age of your horse, what your horse does for a living, and your geographical area. All of these factors will influence which vaccines you give and how you give them. Individuals also have different responses to vaccination as to how robust an immune response they will have or how long it will last. And no vaccine will be effective if it is not given properly. Make sure that you allow your veterinarian to give the proper initial series and boosters for all vaccines. Vaccine schedules for foals have been modified in the last few years based on research. Of greatest note is for equine influenza. Influenza vaccine should not be administered to foals less than 6 months of age due to strong and persistent maternal antibodies. Vaccinating too soon can lead to inadequate protection later in life.
Which vaccines do my horses need?
The American Association of Equine Practitioners (AAEP) and the American Veterinary Medical Association (AVMA) have recently come up with vaccination guidelines. The AVMA has categorized vaccines as core and risk-based. Core vaccines are those “that protect from disease that are endemic to a region, those with potential pubic health significance, required by law, virulent/highly infectious, and/or those posing risk of severe disease. Core vaccines have clearly demonstrated efficacy and safely 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.”
Core equine vaccines include:
- Eastern Equine Encephalitis
- Western Equine Encephalitis
- West Nile
Every horse should be vaccinated for these diseases. Not long ago, there were sections of the country where there was no West Nile Virus. Unfortunately, that is no longer the case. Horse owners should also not become lackadaisical about a disease just because they haven’t heard of any cases in their area or they decide to save money by vaccinating for the disease “du jour” and not some of the basic ones. An example of this occurred in South Carolina when West Nile Virus first entered the state. Many owners chose to vaccinate for West Nile in place of Eastern Encephalitis. Unfortunately, South Carolina was about to experience a normal cyclical outbreak of Eastern Encephalitis that year. Hundreds, possibly thousands of horses died from encephalitis that year because they were not properly vaccinated.
Risk-based vaccines include:
- Rhinopneumonitis (equine herpes)
- Equine Viral Arteritis
- Equine Influenza
- Potomac Horse Fever
- Rotaviral Diarrhea
- Venezuelan Equine Encephalitis
How do I decide which risk based vaccines to give?
Horse owners should formulate a plan with their veterinarian as to which of the risk-based vaccines are appropriate for their horses.
Information in this article is for educational purposes only and is not a substitute for evaluation by an equine professional. In particular, all horse owners should seek advice from a veterinarian for their horses medical needs.