Spring is here! The horse show season has begun and the warm sunny days beg for leisurely trail rides. It is also time for biannual vaccinations for our equine friends. For many of us, spring and fall are the times when we take care of this important element of our horse care. Vaccinations are an important part of any preventive equine health program and they are a highly effective method of preventing certain infectious diseases.

The specific vaccinations we need for our horses depend on several factors: environment, age, use, exposure risk, geographic location, and general management. Vaccinations are recommended for the following core diseases: Equine Viral Encephalomyelitis, Tetanus, Influenza, Equine Rhinopneumonitis, Strangles, Potomac Horse Fever, Rabies, West Nile Virus, and possibly Equine Protozoal Myeloencephalitis (EPM). Along with the vaccinations, a blood sample for Equine Infectious Anemia (EIA), a fatal disease for horses, may be collected at this time. This usually referred to as the Coggins test.

Vaccinations are the best way to protect our horses and ponies against these potentially life threatening diseases. Summer is just around the corner -- with its biting insects, horse shows and long, leisurely trail rides. For relatively little investment, vaccinations prevent diseases that can be expensive to treat, or that may be fatal to our beloved equine friends.

CORE DISEASES

Equine Viral Encephalomyelitis - also known as "sleeping sickness", a contagious brain and spinal-cord inflammation caused by several species of alphaviruses in the Togaviridae family that are usually transmitted by mosquitoes. The disease is characterized by fever, erratic behavior and/or stupor and is almost always fatal. Eastern equine encephalomyelitis (EEE) and Western equine encephalomyelitis (WEE) are present in North America; Venezuelan equine encephalomyelitis (VEE) has not occurred in the United States for some time but outbreaks still occur in South America.

Tetanus - caused by the toxin of Clostridium tetani, an anaerobic bacterium that lives in soil and feces but can infect wounds. The bacteria produce a toxin that affects the horse’s nervous system. Sometimes called "lockjaw," tetanus is caused by toxin-producing bacteria present in the intestinal tract of many animals and found in abundance in the soil where horses live. Its spores can exist for years. Symptoms include muscle stiffness and rigidity, flared nostrils, hypersensitivity, the legs stiffly held in a locked position as the disease progresses, muscles in the jaw and face stiffen, preventing the animal from eating or drinking. More than 80 percent of affected horses die. Luckily, this disease is not contagious.

Influenza - an acute viral infection involving the respiratory tract which is one of the most common respiratory diseases in the equine but is usually not fatal. Influenza is marked by inflammation of the nasal mucosa, the pharynx, the conjunctiva, the lungs and sometimes the heart muscle. The virus is highly contagious and can be transmitted by the air from equine to equine over distances as far as 30 yards, for example, by snorting or coughing. Vaccination cannot guarantee that the horse will not contract the disease.

Equine Rhinopneumonitis - a contagious disease caused by herpes viruses (EHV-1, EHV-4); characterized by fever, mild respiratory infection, neurologic conditions and, in mares, abortion. This disease, like influenza, is rarely fatal, but can cause the horse to be very sick for a prolonged period of time. And like influenza, vaccination cannot guarantee that the horse will not contract the disease. However, horses that have been vaccinated most often demonstrate much milder symptoms than those that have not been vaccinated.

Strangles - a highly contagious infection of the lymph nodes, usually of the head, caused by Streptococcus equi bacteria. Horses can carry the organism in the guttural pouch for at least two years. The abscesses may become so large as to obstruct the airway (hence the term “strangles”) and may break internally, draining a thick, yellow pus through the nose, or externally, draining through a spontaneous or surgical opening in the skin.

Potomac Horse Fever (monocytic ehrlichiosis) - a disease caused by a rickettsial organism, Ehrlichia risticii. Named after the Potomac River Valley where it was first recognized in 1979, the disease is characterized by fever, diarrhea, laminitis, and/or death. The disease is not directly contagious from horse to horse, and it is likely that an insect, possibly a tick, is involved in disease transmission. Potomac horse fever is a seasonal disease, with most cases being identified in late spring to early fall.

Rabies - an infectious viral disease of the central nervous system. It is more common in some areas than others. Equines are infected infrequently, but death always occurs. Rabies has a high level of public significance, as human exposure can be devastating. Rabies can be transmitted
from equines to humans, although there are no reported cases in humans from equine exposure. The rabies vaccine is a “must-do.”

West Nile Virus - a flavivirus transmitted by mosquitoes. West Nile virus can infect horses, humans, birds and other mammals. Signs can include muscle weakness, stumbling, poor motor coordination, loss of appetite, lethargy, fever, impaired vision, circling, head pressing, recumbency, convulsions, coma and death. Infection with this virus does not always cause illness.

Equine Protozoal Myeloencephalitis (EPM) - is a debilitating neurologic disease of horses. Although the incidence of EPM is not high in the population of horses, those horses affected are often severely affected. It can affect the brain, brainstem, spinal cord or any combination of these three areas of the central nervous system. The causative agent of EPM has been identified as Sarcocystis neurona. Clinical signs are vague, but can include weakness, lameness, incoordination, difficulty moving (especially in hindquarters), or in rising from lying down. Signs can also include seizures, weight loss, blindness, loss of balance, head shaking and inappropriate sweating. Possum feces are thought to be the source of the infection for horses. Horses are then affected by eating pasture, hay, grain, or water contaminated with possum feces.

Along with the vaccinations, the spring or fall is also a good time to collect a blood sample for the annual Equine Infectious Anemia check, also known as the Coggins test.

Equine Infectious Anemia (EIA) - also referred to as swamp fever, a serious viral disease. Transmission of EIA is primarily by biting insects. There is no vaccine against EIA, and there is no specific treatment for infected horses. The Coggins test made it possible to identify infected horses even if they showed no signs of illness. EIA virus is a member of the Lentivirinae subfamily of retroviruses. The disease takes one of three forms: acute, chronic or inapparent. A horse suffering from the acute form will have a high fever and will exhibit depression, weakness, poor appetite, weight loss, anemia and usually death. Fluid accumulation may appear under the skin and in the chest, abdomen and legs. The chronic form is less severe than the acute form, and an infected horse may survive; however, the result is a lingering, unthrifty horse that gradually becomes weaker. Horses suffering from inapparent EIA are carriers of the virus but do not display symptoms of the disease. Such horses test positive to the Coggins test but remain apparently healthy. In most states, EIA positive horses must be euthanized. Most states require a negative Coggins test for interstate travel. In addition, most boarding facilities, horse shows and events require a negative Coggins test.

Reference links:
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2072/F-9119web.pdf
http://www.uaex.edu/Other_Areas/publications/PDF/FSA-3059.pdf
http://www.equinevetservice.com/vaccinations.htm
http://www.aaep.org/