Developing A Vaccination Plan For Your Horse
by Great Lakes Equine Wellness Center, Inc.

Have you ever developed a personal “wellness program” for your horse(s)? If not, vaccinations should be included in almost every horse's wellness program.  Each horse should have a vaccination program developed based on its risk of disease and potential for adverse reactions to the vaccines.  You should also take into consideration the cost of the immunization versus the cost of the disease and the zoonotic potential for the disease (if the horse is not vaccinated and becomes infected).   

The purpose of a vaccination program is to contribute to infectious disease control by enhancing resistance to diseases.  However, if good management practices directed at infection control are not incorporated at your farm, vaccination alone may not be sufficient for preventing infectious disease.  Vaccination does not equal immunization.  Also, it is important to note that your horse may not be protected to an equal degree or for an equal amount of time as the other horses on the farm who have received the same vaccinations.

A common concern of owners is the risk of adverse vaccine reactions.  Adverse reactions to vaccines are always a risk, and it is not always easy to predict which horses will exhibit symptoms.  For this reason, it is not commonly recommended to vaccinate your horse two weeks prior to an event, sale, or shipment.  Also, before exposing your horse to a new environment, it is important to allow enough time for the generation of a protective immune response after the vaccination has been administered.  Symptoms to look for that indicate a vaccine reaction has occurred include local muscular swelling and soreness at the injection site, fever, anorexia, and/or lethargy.  Other reactions that may occur include urticaria (hives), purpura hemorrhagica (a disease resulting in cold areas of swelling on the horse, a high heart rate, and purplish-red spots on the mucosa), or anaphylaxis (an unusual or exaggerated allergic reaction).  A preventative step you can take as a horse owner, to decrease the risk of adverse reactions, is decreasing the number of vaccines given on the same day.  There is no safety and efficacy data available regarding the administration of multiple vaccines on the same day.  Also, if your horse has exhibited symptoms of a vaccine reaction in the past, inform the veterinarian.  This will allow the veterinarian to modify the vaccination program for your horse. 

For our clinic, there are several diseases that are commonly vaccinated against.  The following is a brief summary of each of the diseases, to give you an appreciation for the importance of the vaccine. 

Tetanus (“Lockjaw”): Often fatal disease caused by a potent neurotoxin produced by the bacteria Clostridium tetani.  This bacterium is present in the soil, the intestinal tract, and feces of horses.  The disease is not contagious but occurs when Clostridium tetani infects puncture wounds, lacerations, surgical incisions or exposed tissue such as the umbilicus of foals.  Tetanus toxoid is the vaccination and should be given to all horses annually.  Vaccinated horses should be boostered if they have a wound or surgery more than 6 months after their previous booster.  Tetanus antitoxin is given to unvaccinated horses or foals born to an unvaccinated mare when immediate protection against tetanus is necessary.

Equine Encephalomyelitis (EEE, WEE, Sleeping Sickness): A viral infection transmitted to horses by mosquitoes and other bloodsucking insects, which have acquired the virus from birds and rodents.  The virus causes swelling of the brain and spinal cord, resulting in neurologic symptoms. 

West Nile Virus (WNV): A viral disease new to Wisconsin in 2001.  WNV is carried by birds (most commonly crows and blue jays) and is transmitted most commonly to horses and humans by mosquitoes.  The virus causes encephalomyelitis or inflammation of the brain and spinal cord.  It is fatal about 40% of the time. 

Rabies: A viral disease that affects the central nervous system of mammals and is 100% fatal.  It is transmitted through the saliva of infected animals.  Rabies can be transmitted from infected horses to humans.  All horses should be vaccinated yearly. 

Equine Influenza (Flu): A highly contagious viral respiratory disease causing signs similar to human cold symptoms (i.e. cough, nasal discharge, fever, depression, and loss of appetite). Influenza is transmitted by aerosol (coughs or snorts) from horse to horse over distances as great as 30 yards.

Equine Herpesvirus (Rhinopneumonitis, EHV): A viral disease in which two distinct viruses, EHV-1 and EHV-4, cause two different diseases.  Both strains cause respiratory tract disease characterized by fever, lethargy anorexia, nasal discharge and cough.  EHV-1 may also cause abortion, foal death, and paralytic neurologic disease.  Rhinopneumonitis is spread by both aerosol routes and direct contact with secretions, equipment, or drinking water.  The virus may be present but inapparent in carrier animals.  Consistent vaccination appears to reduce the frequency and severity of disease. 

Strangles (Streptococcus equi, Equine Distemper):
A highly contagious disease caused by the bacteria Streptococcus equi.  The organism is transferred by direct contact with infected horses or sub-clinical carriers, or indirectly by contact with nasal discharge or pus from draining nodes that may contaminate equipment, pastures, stalls, or water and feed troughs.  The disease often causes enlargement and abscesses of lymph nodes of the head, jaw, and throat.  Occasionally it can cause a serious generalized vasculitis called purpura hemorrhagica.

Potomac Horse Fever (Equine Monocytic Ehrlichiosis): PHF is caused by Ehrlichia risticii, which has been linked with fresh water snails and water insects.  Cases are frequently seen in our area, especially during warm, wet years.  The disease is seasonal, often occurring between late spring and early fall with the majority of the cases occurring in July, August, and September.  The organism is picked up from the environment and the disease cannot be transmitted from horse to horse.  Clinical signs vary but include fever (102-107F), lethargy, anorexia, mild to profuse diarrhea, colic, dehydration, and laminitis.  A relatively large proportion of horses die or are euthanized due to serious complications such as laminitis.