If you own an equine, you recognize the value of modern immunizations and welcome the peace of mind that a good vaccination program provides.

Unfortunately, immunization options and protocols can be confusing and difficult to understand for even the most seasoned equestrian.

For example:

? What does a horseman mean when he says he vaccinated with a "five-way," or a "four-way,"?

? When should a horse be vaccinated for West Nile virus?

? How often should a horse receive a tetanus vaccination - and what are the implications of choosing not to vaccinate?

? What about vaccinating for strangles?

? Why isn't vaccinating horses and mules for rabies a common practice like it is in dogs and cats?

? What is "rhino" anyway? What about botulism, influenza, and Potomac horse fever?

? Are vaccinations 100% effective?

? What are the side effects associated with equine vaccinations?

? And finally, what does my horse really need to be immunized against?

Vaccinology: How do Vaccines Work?

Vaccines provide a method of exposing a horse's immune system to an infectious disease. Once the immune system learns to recognize the disease it develops antibodies (or protective proteins) against the specific disease.

Most modern vaccinations are developed in scientific laboratories such that the immune stimulating ingredient has been changed or masked in some way so that it no longer causes disease.

While new vaccines are being developed that do not require injections, the most common way to vaccinate a horse is by intramuscular injection.

Unfortunately, while most vaccines provide a high level of protection, they do not guarantee 100% immunity. This is due to many complicated reasons, such as rapidly changing pathogens (like the influenza virus), variation between individual horse's immune response to vaccinations, the length of time the immune system maintains protective antibodies to a specific bug, whether or not a vaccine was handled appropriately, and the list goes on.

Once a horse has been vaccinated, the protective antibodies in the horse's blood stream are prepared to defend the horse against invasion by disease- causing pathogens. Over time, however, the number of protective antibodies decreases, leaving the horse, once again, susceptible to infection and disease. A booster vaccination is then required to maintain a sufficiently high concentration of protective antibodies. Under most circumstances, yearly boosters keep the immune system sufficiently armed against infectious diseases.

What Vaccines Does my Equine Need?

This question is best answered by answering the following questions: What is the risk of exposure to various disease causing pathogens? (consider: environmental factors, geographic factors, age and gender of the horse as well as anticipated exposure).

Recently, the American Association of Equine Practitioners released a vaccination guide that divides vaccines into two categories: Core Vaccines and Risk-Based Vaccines.

Core Vaccines

Core vaccines are defined as those vaccinations that "protect against diseases that are endemic to a region, are virulent/highly contagious, pose a risk of severe disease, those having potential public health significance, and/or are required by law.

Core vaccines have clearly demonstrable efficacy and safety, with a high enough level of patient benefit and low enough level of risk to justify their use in all equids."

Core vaccines include: tetanus, eastern/western equine encephalomyelitis, West Nile Virus, and Rabies.

Risk-Based Vaccines

Risk-Based Vaccines "are selected for use based on risk assessment performed by, or in consultation with, a licensed veterinarian.

Use of these vaccines may vary between individuals, populations, and/or geographic regions."

Vaccination against the following diseases are considered risk-based: Influenza, equine herpes virus (rhino), strangles, rotavirus, potomac horse fever, Equine viral arteritis, anthrax, and botulism.

Vaccine induced immunity against core diseases and the most common risk based diseases can be achieved by vaccinating with a five-way, combination vaccination, which typically provides protection against three of the core diseases (Eastern and Western equine encephalomyelitis, tetanus ) and two risk-based diseases (equine herpes virus (rhino), and influenza).

In addition to vaccinating with a five-way vaccine, horses and mules require a West Nile Vaccine as well as vaccination against rabies in order to be protected as outlined by the American Association of Equine Practitioners.

When to Vaccinate:

Once again, the answer to the question of when to vaccinate is best determined by considering the following: age, intended use, and anticipated exposure.

Historically, mature animals received booster vaccinations each the spring. This is a logical time of year to vaccinate horses since they experience increased exposure to disease- causing pathogens during the summer months - increased travel, mosquitoes, and increased exposure to new horses (that may not be vaccinated).

In addition to springtime booster vaccinations, horses that are exposed to disease-causing pathogens throughout the summer may benefit from booster shots that will help maintain a high level of immunity.

For example: The immune response to the influenza vaccine is relatively short-lived and a booster may be required every three to six months.

Horses in regions of high mosquito concentrations that spread West Nile virus or a particularly long mosquito season, may benefit from a booster shot mid-way through the summer. Tetanus boosters should be administered to all horses that have sustained a puncture wound or laceration or are scheduled for elective surgery. Special consideration should be given to horses used for breeding purposes (both stallions and mares).

Other Vaccines:

Vaccination against Strangles, Rotavirus, Potomac Horse Fever, Equine Viral Arteritis, Anthrax, and Botulism are best administered after carefully considering the principles of vaccination, the efficacy of the vaccine and the risks associated with the specific vaccines.

Your veterinarian can help you determine if vaccination against these diseases is appropriate for your horses or mules.

Take Home Message:

Collaborate with your veterinarian to tailor a vaccination strategy that best suits your equine based on exposure and risk.

Once you have determined the best approach to vaccinations, ensure that your animal receives those vaccines annually in order to protect your animals and set your mind at ease.

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