Equine Vaccines

The Importance of Equine Vaccines: Protecting your horse from infectious disease

Vaccinations are important to help protect horses from infectious diseases that are detrimental to them, if not deadly. However, owners must have realistic expectations and realize that vaccinations alone without good management practices directed at infection control, is not sufficient for the prevention of infectious disease.  Outbreaks and occurrence of infectious diseases in horses tends to increase with increased population density, movement of horses on and off the facility, and environmental and managerial influences, such as stress, parasitism, inadequate sanitation, and poor nutrition.  By minimizing these external factors, along with appropriately administering vaccinations prior to likely exposure, we can minimize the risks of infection and enhance resistance to those diseases.

There is a group of “core” annual vaccinations that we recommend to every horse.  There are four very important infectious diseases that we vaccinate horses for annually.  These are: (1) Western and Eastern encephalomyelitis, (2) West Nile virus, (3) Tetanus, and (4) Rabies.  The incidence of these diseases has decreased since better vaccinations have become available and since we are vaccinating our horses more regularly and effectively.  However, we still see them, even herein Lake County.  Just two years ago, we diagnosed two horses with West Nile.  In the past years we have also seen Tetanus.  And just this year, there were four human fatalities in Florida from Eastern equine encephalitis.

Western equine encephalitis, Eastern equine encephalitis, and West Nile virus are all diseases that cause inflammation of the central nervous system.  These viruses cause neurological signs in horses that are very debilitating. They can even cause death. All of these viruses are diseases of wild birds that are transmitted to horses and humans by mosquitoes.  Besides vaccinations, it is very important to minimize the amount of mosquitoes on the property by getting rid of stagnant water, keeping sanitary conditions, and also protecting yourself with mosquito repellent.  Vaccinations should be given annually, ideally prior to vector season in the spring.  In unvaccinated horses, there need to be two shots given 4 weeks apart initially,then annually thereafter.  Pregnant vaccinated mares should be vaccinated 4-6 weeks before foaling.  Foals of vaccinated mares can begin a three-shot series at 4-6 months of age, but if they are from unvaccinated mares, these should begin at 3-4 months of age.

Tetanus is an often fatal disease caused by a potent neurotoxin from the bacteria Clostridiumtetani.  These organisms are present in the intestinal tract and feces of horses, other animals and humans, and are abundant in the soil.  The spores can survive in the environment for many years, resulting in an ever-present risk of exposure on equine facilities.  It is not a contagious disease. Tetanus is the result of C. tetani infection of puncture wounds, open lacerations,surgical incisions, and exposed tissues (i.e. umbilicus of foals and reproductive tract of the postpartum mare).  Tetanus causes spasms of the muscles that lead to paralysis and death.  In the early stages of tetanus, signs include protrusion of the third eyelid, twitching and spasm in the ears, drawing back of the lips, flaring of the nostrils, the appearance of a stiff neck and abnormal carriage of the tail.  As the problem develops, marked stiffness in the limbs("sawhorse stance"), difficulty swallowing and drinking("lockjaw"), difficulty standing, profuse sweating, and respiratory distress occur.   In order to help prevent this disease, vaccination with the tetanus toxoid vaccine is very important, as well as cleaning wounds thoroughly, and keeping sanitary conditions.  The vaccine protocolis the same as the vaccines for the encephalitides.  The only difference is that horses that sustain a wound or undergo surgery 6 or more months after their previous booster should be revaccinated with tetanus toxoid immediately at the time of injury or surgery.

Rabies vaccine is the last of the “core” vaccinations.  Rabies is an infrequently encountered neurologic disease of horses.  However, although the incidence of rabies in horses is low, the disease is fatal and has considerable public health significance.  It is contagious to humans as well as other animals.  Rabies occurs through the bite of an infected (rabid) animal, typically a wildlife source such as raccoon,fox, skunk, or bat. Bites to horses occur most often on the muzzle, face, and lower limbs. The virus migrates via nerves to the brain where it initiates rapidly progressive, invariably fatal encephalitis.  Vaccination is critical to help prevent this disease.  The rabies vaccine is an annual vaccine.  It should also be given to pregnant mares 4-6 months prior to foaling. In foals of vaccinated mares, it should be give at 6 months of age, boostered 4-6 weeks later, then annual thereafter.  In foals of unvaccinated mares, it should be given at 3-4months of age, then annual thereafter. 

Legally,the rabies vaccine must be administered by a licensed veterinarian.  However, all vaccinations should be given by a licensed veterinarian to assure that viable vaccine is utilized and injections are properly administered. Mistakes in vaccination protocol by well-meaning horse owners can result in ineffective protection in an animal that was thought to be risk free. All too frequently, owner vaccinated horses develop overt cases indicating that the animal was improperly vaccinated or was vaccinated with vaccine that had lost its protective properties. Properly administered vaccinations are effective for only one year, thus, booster shots are required on an annual basis.  It is also important to be aware that each horse in a population is not protected to an equal degree or for an equal duration following vaccination. All horses in a herd should be vaccinated at intervals based on the veterinarian’s opinion.  Ideally,the same schedule is followed for all horses in a population, thus minimizing transmission of infectious agents in a herd and indirectly protecting those horses in the herd that responded poorly to vaccination.

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