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Horse Health: Vaccinations

How many times do both owners and veterinarians take the “simple” things for granted?  The last time you called your veterinarian to schedule your horse’s routine shots, how much thought did you put into what you were doing?  For example, what does your horse need to be vaccinated for?  Wouldn’t it just be simple to say, “Let’s give all of the available vaccines, and deworm with the best product on the market!”  Why don’t we do such things for our horses?  The reality is that the “simple” things aren’t always that simple.  Let’s focus now on vaccine protocols for our horses.

Equine Vaccine Protocol

The American Veterinary Medical Association has defined a Core Vaccine as one that protects from a disease that is endemic to a region, those with potential public health significance, those required by law, those that protect from highly virulent/highly infectious diseases, and/or those that protect against diseases that pose a risk of serious illness.  Based on these guidelines, the American Association of Equine Practitioners has established that in horses the core vaccines include rabies, Eastern/Western equine encephalomyelitis (EEE/WEE), tetanus, and West Nile Virus.  Additionally, Core Vaccines are those that have been a clearly demonstrated level of safety and efficacy, and therefore have a high level of patient benefit compared to a low level of risk to the patient.  At this point it is important to remember that there are always risks with any procedure performed on a patient, even the “simple” things.  Adverse reactions can occur in a patient, and thus should be monitored for, and reported if they occur.  We’ll save this point for later however!

What Vaccines Should Your Horse Receive?

When designing a vaccine protocol for your horse, there are several things that should be considered. The big factors that aid in the development of an appropriate vaccine protocol include risk factors for the patient, consequences of the disease, efficacy of the vaccine, cost of the immunizations, and cost of the disease.  Obviously there are multiple things to consider with each of these individual factors, so even more thought has to go into this.  When thinking about risk factors to the patient for example you should consider things such as exposure risk and geography.  For example, a horse in Arizona is not at risk for Potomac Horse Fever, and thus does not need this vaccine as part of its vaccine protocol even though PHF can be a very costly disease to treat.  The Arizona horse is highly unlikely to be exposed to PHF due to the geography of the disease and the fact that a portion of disease transmission involves freshwater snails, and thus the exposure risk in an arid climate like Arizona is very low.  In comparison, providing immunization of Rhinopneumonitis and Influenza would be recommended as part of a typical vaccine protocol, because they are common respiratory diseases found all over the US including Arizona.  As a side note, Rhino is caused by the EHV-1 virus which has gained a marked amount of press recently due to the recent outbreaks of the myeloencephalitic (neurologic) form of EHV-1.  It is important to understand that currently there are no EHV-1 vaccines labeled to prevent the myeloencephalitic form of EHV-1.  However continuing to vaccinate against EHV-1 may help to reduce nasal shedding of the virus and thus potentially help to limit the spread during outbreaks.

Adverse Reactions

As promised, let’s look at potential adverse reactions to our horses due to vaccinations.  To attain a label for use in animals, a vaccine must be first approved for efficacy and safety.  Despite the fact that all commercially available vaccines have undergone safety testing, adverse reactions are still a possibility, and will occur in some horses.  Unfortunately for both the veterinarian and the horse owner, vaccine reactions are not always predictable.  Vaccines are designed to stimulate a horse’s immune system so that it can mount a response when exposed to certain diseases.  Since what is being given to the horse is meant to stimulate the immune system, then certain side effects, such as potential fever or muscle soreness and malaise (a general dull feeling) not uncommon.  More severe side effects are also a potential in our horses, and these could include abscess formation, muscle necrosis (death of muscle tissue), or anaphylaxis (severe, potentially life-threatening allergic reaction).  Any time that an adverse reaction is encountered in a patient, it is important that it be reported to the manufacturer so that they are monitored and dealt with appropriately.  Due to the potential for serious adverse reactions, it is also recommended that all vaccines be given by, or under the direct supervision of a veterinarian.  This will allow for someone to be immediately available in the event of one of the more serious adverse reactions.

A Team Effort

As you can see not all of the “simple” things are truly that simple.  Thought and education, both on the part of the owner and the veterinarian, should go into the development of a vaccine protocol.  The best way to gain this education is to first maintain an excellent dialogue with your veterinarian.  Often times it is easier for a veterinarian to attain and assess the science behind the various vaccines available, so that the right one is selected for your horse, and obviously that is and always will be the most important aspect of health care!

Dr. Mike Cissell

Board Certified Large Animal Surgeon

Prescott Animal Hospital Equine Center