Page 30 - New Mexico Summer 2021

VACCINATIONS
by Megan Petty, DVM
These days vaccination is a topic of much conversation thanks to our new companion COVID-19. While the general public is not as familiar with routine vaccination, horse owners around the world know it’s a part of the yearly and often bi-yearly routine. Equine vaccinations broadly fall into one of two categories: Core vaccines or Risk-Based vaccines. The difference
is in the type of disease that is being targeted. The American Veterinary Medical Association defines core vaccinations as those that “protect from diseases 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 most patients.” Or as I often more simply explain it, “They target the diseases that can come to your horse and kill it.” In our equine compan- ions, the core vaccines are those that protect against Eastern/Western/Venezuelan Equine Encephalomyelitis, West Nile Virus, Tetanus, and Rabies. The risk-based vaccinations are included based on what amounts to a risk-benefit analysis of the lifestyle of your horse. The use of these vaccines will vary from region to region and from population to population within that given area, and even within those individual popula- tions. Some diseases targeted by risk-based vaccination that you may be familiar with (and specific to our racing and breeding horses in New Mexico) include Equine Viral Arteritis,
Equine Influenza, Equine Herpesvirus/ Rhinopneumonitis, and Strangles.
Before we dive into some of the specifics of the diseases we are targeting, it is important to realize that there is no “standard” vaccination program for all horses. Evaluation of the risk of disease, consequences of disease, effectiveness of the product, and potential for adverse reaction should all be considered when designing a vaccination protocol for your horses. Certain classes of horses will have a higher risk of disease than others if they travel more and thus have more potential exposure to infective agents. Additionally, older horses may be at higher risk for infection due to an immunocompromised state, but may have a higher risk of adverse reaction to certain vaccines. Be sure to consult with your veterinarian to determine which vaccinations to provide to each horse (or each class of horse) in your herd. A few other key points to understand are:
1. Vaccination alone, in the absence of good management of infection, is not enough to prevent disease.
2. Vaccines minimize the risk of infection but cannot prevent disease in all circumstances.
3. Protection is NOT immediate with vaccines designed to provide active immunity (most require a primary vaccine followed by boosters spaced in specific intervals).
4. Primary and booster vaccinations should be administered prior to exposure, and there is always risk of adverse reaction, even with proper handling of vaccines.
5. Each horse in each population is not equally protected to the same degree nor for the
same amount of time. However, thanks to herd-immunity this point is not often of great concern within a herd of vaccinated equines.
Core Vaccination Diseases
Eastern/Western/Venezuelan Equine Encephalomyelitis (EEE, WEE, VEE): these diseases cause neurologic symptoms in horses and are transmitted primarily by mosquitoes (referred to as the vector) and infrequently by other insects, ticks, or nasal secretions. There is a high mortality rate associated
with these diseases, which is why they make the list for core vaccination. VEE falls more into the risk-based category as it is more a culprit of outbreaks in Central and South America and Mexico. However, it occasionally makes an appearance in the southern US
and is considered a reportable foreign animal disease. EEE and WEE are found, as their names imply, in the eastern or western parts of the US. Commercially available vaccines for all 3 diseases are available and should be administered to adult horses prior to vector season in the spring as a primary vaccine followed by a booster if the horse has never been vaccinated before. Annual boosters are recommended, but more frequent vaccination may be required based on geography and immune status of the horse.
West Nile Virus: this is another neurologic disease of horses and has a fatality rate of 33%, but with as much as 40% of survivors showing residual abnormalities such as gait and behavior changes 6 months after diagnosis. These residual neurologic changes are why WNV makes the list of
core vaccinations. WNV is spread from bird reservoir hosts by mosquitoes to horses and humans. However, horses and humans are considered “dead-end” hosts as the infection is not directly spread from horse to horse
Core vaccinations are defined as those that “protect from diseases 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 vaccinations protect against diseases with a high mortality rate, including against Eastern/Western/Venezuelan Equine Encephalomyelitis, West Nile Virus, Tetanus, and Rabies.
28 New Mexico Horse Breeder