On January 27, 2019 at IaDCTA’s annual banquet Dr. Pat Foley presented comprehensive information on the importance of vaccinating our horses. The exposition placed emphasis on the most devastating diseases and those most likely to affect our animals in Iowa. She has made a follow up account as a reminder and a review that can be saved for future reference.
Thank you Pat Foley for taking the time to help us be better partners in our horse activities.
Considerations for Vaccinating Your Horse
Against Critical Equine Diseases
Pat Foley, DVM, PhD (Immunobiology)
There are many equine diseases that affect horses, sometimes fatally. There are numerous vaccines that can mitigate the adverse effects of these diseases. The American Veterinary Medical Association (AVMA) has defined 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.” Per the American Association of Equine Practitioners (AAEP), there are certain core vaccines that all horses should receive to protect them against the worst pathogens they are likely to encounter. These core vaccines are against rabies virus, encephalomyelitis viruses, West Nile virus, and Clostridium tetani, i.e. the bacterium causing tetanus. Other than rabies vaccine, they are manufactured in combination products, so that a single injection can provide vaccination against numerous pathogens.
Other types of vaccines may be recommended when certain risk factors are present that suggest their use. Risk-based vaccines include those that protect against Potomac horse fever, strangles, influenza, and equine herpesvirus, but there are others, as well.
It is important to give vaccines in sufficient time, about 3-4 weeks prior to expected exposure, e.g. prior to mosquito season for those insect-borne viruses. This gives the immune system time to react and develop protective immune mechanisms against the pathogen. For this reason, in North America, spring vaccinations are considered most critical. In some cases, where mosquito season is extended or the duration of immunity is limited, a second vaccination six months later may be recommended.
Other considerations regarding type and frequency of vaccination are the age of the horse, type of the horse’s activity (e.g., breeding, travel, and/or competition), the risk of exposure, prevalence of the disease, and prior vaccination history. Also, instructions on proper storage and preparation, how to administer and when, the number of doses, etc., will vary with different products. Because of the many considerations around the most effective use of vaccines, your veterinarian should be consulted regarding their best usage in your specific situation. General recommendations for broodmares, previously vaccinated and unvaccinated adult horses, weanlings, and foals are provided on the AAEP website: https://aaep.org/guidelines/vaccination-guidelines/core-vaccination-guidelines
For an initial vaccination, generally two doses 3 weeks apart are required to adequately activate an immune response. These are followed by annual or, in some cases, semiannual boosters. Some owners don’t vaccinate their horses well, believing that vaccination itself can pose risks to the horse or that vaccines are not worth the expense. It should be stressed that the benefits far outweigh the risks, that a serious adverse event is far less likely to occur than a successful, uneventful vaccination, and that the cost of disease is far more expensive. Potential death due to infection by these pathogens can be avoided with appropriate use of the core vaccines. Rabies, for example, is 100% fatal and can be transmitted from horse to human through the saliva of an infected animal. Tetanus results in rigid paralysis that often leads to death. Encephalomyelitis, West Nile virus, and equine herpesvirus can cause neurologic symptoms so severe, a horse may have to be humanely euthanized. Other diseases such as Potomac horse fever, strangles, and influenza are not considered deadly but can have profound effects on the health of your horse and may require long recovery periods. Although a vaccine may not prevent infection by these various pathogens, they can decrease severity of clinical disease and should be used when recommended by your veterinarian.
Lastly, keep a record of the vaccines you have given, critical to maintaining your horse’s health and especially useful in the event of potential exposure to infected horses or their environment.