Lauren Jacobsen, DVM

What are vaccines and why do we use them?
A vaccine is a dampened-down version of a disease (usually viral, bacterial, or parasitic) that is administered into the body to augment the immune system’s ability to recognize that particular disease and shorten the time frame and increase the strength needed to fight it. After the initial vaccine, they are given at scheduled intervals to “boost” or refresh the memory of the immune system. Vaccines can be given either in the muscle (intramuscular, IM) or in the nose (intranasally, IN). The route used for vaccine administration is dependent on the type of vaccine and the disease you are trying to protect the animal from. Vaccines can be manufactured in combinations, such as the “4-way” and “5-way” or can be produced in their individual form. The “4-way” vaccine includes tetanus, eastern and western encephalitides, and influenza. The “5-way” combo has the same ingredients with the addition of rhinopneumonitis.

Below is a brief overview of the most common vaccines that may be given to your horse. These include the following: tetanus, eastern and western encephalitidies, west nile virus, rabies, rhinopneumonitis, influenza, and strangles. A vaccination schedule is not provided because it is dependent on many different factors including but not limited to age, previous vaccination history, risk of exposure, geographical status, life stage (ie: pregnant mare vs. non-pregnant mare, stage of her gestation, etc.), surrounding animal population, etc. To figure out what is best for your horse or herd, talk with your veterinarian to develop a plan.

All animals are at risk of getting tetanus and horses, donkeys, mules, and minis are particularly sensitive to it. The bacterium, Clostridium tetani, is responsible for this fatal neurologic disease. While it is not contagious, it is found in the soil, manure, and gastrointestinal tract of the horse so there are plenty of opportunities for the equine body to come into contact with it. Times when your animal is at risk of acquiring tetanus include puncture wounds, open lacerations, surgical incisions, exposed flesh, etc. The tetanus vaccine is very effective at preventing disease.

Eastern and Western Equine Encephalidities (EEE and WEE)
Eastern Equine Encephalopathy (EEE) and Western Equine Encephalopathy (WEE) are neurologic diseases caused by a virus. It is transmitted by mosquitoes. Humans can also get these diseases. The fatality rate is high with these viruses but thankfully the vaccine has a high protection rate.

West Nile Virus (WNV)
WNV is a neurologic disease caused by a virus. Horses with WNV can show signs such as stumbling and incoordination. Similar to EEE/WEE, it is also transmitted by mosquitoes and can also infect humans. WNV is typically transmitted from birds to human or horse but is not transmitted from horse to human (or vice versa). WNV is offered as an individual vaccine and as well as in combination with other vaccines.

Rabies is caused by a virus and also results in a fatal neurologic disease. Horses with rabies can show signs of aggression, excessive salivation, as well as depression. This disease is rapidly fatal. In the unvaccinated horse, he or she will die from the disease before the animal’s immune system can have a chance to respond. Therefore, vaccination against this disease is important because it gives the immune system an idea of what the virus looks like so that it already has a preformed army should the horse come in contact with the virus. If your horse is exposed to wildlife (ie: raccoons, foxes, skunks, bats, etc.), consult with your veterinarian about getting this vaccine for your horse. The rabies vaccine is a solo vaccine.

Herpes (equine herpes virus, types 1 and 4)
Rhinopneumonitis, or sometimes termed as “Rhino”, is caused by the herpes virus, specifically equine herpes virus, types 1 and 4. It can cause abortion in pregnant mares and respiratory disease in any age of horse. This virus is contagious and transmitted by either touching or inhaling infected aerosol droplets from the horse when he/she coughs. It can also be transmitted by infected nasal secretions. Young animals are at highest risk and are therefore usually the ones most commonly vaccinated. Pregnant mares are routinely vaccinated at regular intervals as well to provide adequate levels of antibodies in the colostrums for the upcoming foal. They should be boostered with this vaccine at months 5, 7, and 9 of her gestation. There is also a neurologic strain of the herpes virus (equine herpes virus, type 2). Horses with the neurologic strain of herpes can show signs of incoordination, difficulties with urination, etc. Unfortunately, there is no vaccine available at this time that can provide adequate, reliable protection without side effects. While the rhino (types 1 and 4) vaccine is offered as a combination with the “5-way” as mentioned above, it is also offered as a solo vaccine.

Influenza (Flu)
Influenza is caused by a virus that attacks the respiratory system. The flu virus is highly contagious and is transmitted by the same routes as herpes (aerosolized droplets from coughing, nasal secretions, etc.). Animals that are high risk include young animals and those that are in frequent contact with large populations of horses (ie: show animals). The vaccine for flu is short lived; therefore, it needs to be boostered regularly. Your horse’s age and exposure status will reflect the vaccination frequency needed. To help minimize introduction of this virus when you bring a new horse onto your property, it is a good idea to quarantine that animal. A good rule of thumb is to quarantine any new horse to your property for at least 2 weeks. This will help minimize the introduction of this virus onto your farm as well as other diseases. This vaccine is also offered as a solo in addition to the combo. As a solo vaccine, this vaccine is typically found in the intranasal form, unlike its form in the “4 way” and “5 way” where it is given in the muscle.

Strangles is a highly contagious disease caused by the bacteria Streptococcus equi. It is commonly known as equine distemper or dryland distemper. This disease is characterized by high fevers and swollen, painful (and sometimes abscessed) lymph nodes along the jaw line. Other signs may include nasal discharge, decreased/ absent appetite, difficulty swallowing, difficulty breathing, abnormal noises created when breathing, draining lymph nodes, etc. When the lymph node becomes enlarged or swollen, it puts undue pressure on the trachea and laryngeal region of the respiratory tract. Historically, the lymph nodes would become so large that they would compress the airway, hence, the name “strangles”. While this is still a potential concern, we have better techniques of managing horses that acquire this disease. Occasionally, abscesses develop in internal lymph nodes, which is where the terminology “bastard strangles” came from. Young horses are in the high risk population of getting strangles. It is transmitted either by direct contact with the pus that is draining from the lymph nodes, nasal secretions, aerosol droplets from coughing, etc. or through indirect means. Examples of indirect routes of transmission include, but are not limited to, tracking the bacteria on your shoes or clothing after leaving the stall, feed bunks, pastures, stalls, trailers, tack, grooming equipment, etc. An occasional side effect of this vaccine is called purpura hemorrhagica and is more commonly found in adults and older horses. It is an immune-mediated response by the body to the bacteria or vaccine characterized by generalized swelling, especially in the legs. This typically happens in older horses that have received the vaccine at some point in the past or in a horse that has seen the bacteria due to an infection and has been vaccinated after it has recovered from the infection. The strangles vaccine does not prevent your horse from getting strangles but can hopefully limit the severity of the disease. The strangles vaccine is very reactive and should be handled carefully. There are different forms of the vaccine; some need to be given intranasally and others are given in the muscle.

Common misconceptions about vaccines:

*Vaccines are an effective way to keep the immune system “on its toes”, or minimize the risk or severity of infection. Vaccines cannot, however, prevent disease in all circumstances. They should also not be used in place of good management practices and it is impractical for the vaccine to provide sufficient protection without good management practices set in place.

*An animal is not protected immediately after the vaccine is given. The immune system needs an adequate amount of time to respond to the vaccine and prepare its army (the antibodies) for when it will be needed. This takes approximately 2-4 weeks following a booster

*There is no “one size fits all” vaccine program. Many factors, including the horse’s age and life stage, environment, geographical status, surrounding animal population, etc. are used to formulate the appropriate vaccination program for your animal.

*The amount of protection is not the same with all vaccines. This is why some vaccines are boostered annually, and others are done more or less frequently.

*Vaccines need to be given at the appropriate time of year and if applicable, scheduled accordingly with the animal’s life stage. This will yield the best possible protection that the vaccine can provide.

*There are many different kinds of vaccines on the market. There are also a variety of pharmaceutical companies that manufacture these vaccines. Due to the variability in production of the vaccine and type of vaccine, not all vaccines for the same disease can be created equal.

*Most vaccines cannot directly cause the disease that you are vaccinating against, although they may cause temporary stress on the immune system allowing the horse to be more susceptible to disease in general. A reaction in the tissues at the site of injection can be anticipated but it is unlikely to be caused by the agent in the vaccine itself, but rather it is likely due to the adjuvant, which is the part of the vaccine which makes the agent more identifiable to the immune system.

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