Equine Diseases
| West Nile Encephalitis | Description: West Nile encephalitis is a mosquito-borne disease causing inflammation of the brain and spinal cord. Since its discovery in 1999, the virus has spread rapidly across the country, infecting horses, birds, and humans in nearly every state in the continental United States. One in three horses that becomes clinically ill with the West Nile virus will die or be euthanized.
Transmission: Migrating infected birds can carry West Nile encephalitis. Mosquitoes become the vector after they take a blood meal from an infected bird. Infected mosquitoes transmit the virus to other birds and mammals including horses and humans. Horses are a "dead end" host because the concentration of the virus in their blood is too small to infect mosquitoes and continue the cycle. Therefore, horses do not transmit the disease to humans or other horses.
Clinical Signs: Fever, stumbling or tripping, muscle weakness, twitching, partial paralysis, head pressing, inability to rise, convulsions, coma, and death. |
| Equine Herpes Virus (EHV) or Rhinopneumonitis—"Rhino" | Description: Equine herpes virus is a contagious viral upper respiratory disease caused primarily by herpesviruses EHV-4 and EHV-1.
Transmission: The virus is airborne and spreads from horse to horse by nasal secretions or by exposure to aborted fetuses, membranes, and fluid.
Clinical Signs: Fever, loss of appetite, nasal discharge, ocular discharge, weight loss, coughing, and depression. In neonates, the disease is characterized by clinical signs of weakness, poor doers, pneumonia, and often death. EHV can also cause abortion and neurological disease. |
Equine Influenza | Description: Equine influenza is a highly contagious viral upper respiratory disease seen in horses of all ages, but mainly in younger horses (2 to 3 year olds).
Transmission: The virus is airborne and highly contagious, passed from horse to horse by nasal secretions. It is possible asymptomatic horses may carry and shed the virus when stressed.
Clinical Signs: Fever, loss of appetite, nasal discharge, ocular discharge, coughing, and depression.
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| Equine strangles (Streptococcus equi) | Description: Streptococcus equi is the bacteria which causes equine strangles. It is highly contagious and occurs mainly in young horses. Transmission: The bacteria is transmitted by direct contact with infected nasal and abscess discharge. It can also be transmitted by people or fomites, such as tack, brushes, clothing, and water sources. Some horses are asymptomatic carriers and shed during times of stress. Young horses are most commonly affected, while older horses may be susceptible if not previously exposed or vaccinated, or if they are immunosuppressed.
Clinical Signs: The disease commonly results in lymph node swelling in the upper respiratory tract and abscess. In addition, animals may experience depression, anorexia, weight loss, fever, cough, colic, nasal discharge, and reluctance to swallow. |
| Equine Encephalomyelitis | Description: Equine encephalomyelitis is a viral disease affecting the central nervous system (brain and spinal cord). The predominant encephalitides in the Western hemisphere are Eastern (EEE), Western (WEE), and Venezuelan (VEE). VEE has not been present in the United States recently, but there is always the potential that it could cross from Mexico. Consult your local equine veterinarian regarding recommendations for vaccination against VEE in your area.
Transmission: Equine encephalomyelitis is a mosquito-borne disease. Various birds, small mammals, and reptiles are reservoirs and serve as a source of virus for mosquitoes. Infected mosquitoes transmit the virus when they feed on the horse (or human). The horse is a dead-end host (does not transmit the virus to other horses or humans) because the level of virus circulating in the blood is insufficient to reinfect mosquitoes.
Clinical Signs: Fever, anorexia, depression, muscle stiffness and tremors, ataxia, head pressing, circling, facial paralysis, seizures, and a pendulous lower lip. The disease can progress to recumbency, respiratory paralysis, and death. Other diseases that may resemble these include West Nile encephalitis, the neurological form of equine herpes virus, and rabies. |
| Tetanus | Description: Tetanus is caused by a spore-forming bacteria found in the soil and requires an anaerobic (without oxygen) environment to survive.
Transmission: It is most commonly caused by contamination of a wound, where damaged tissue provides the proper environment for bacterial growth and secretion of neurotoxins.
Clinical Signs: Spastic contraction of muscles (most commonly the facial muscles or "lockjaw"), a "sawhorse" stance (rigid extension of the limbs), prolapsed third eyelid, erect ears, and sardonic grin from facial muscle. |
Intestinal Parasites | Description: Internal equine parasites are virtually everywhere in the environment and infect almost every horse. If left unchecked, these tiny invaders can cause poor performance, reduced feed efficiency, diarrhea, weight loss, and even death.
Small strongyles (Cyanthostomes) are the most common and economically devastating parasites of adult horses. Small strongyles are dangerous because of their unique ability to encyst inside the horse's intestinal wall for years at a time.
Bots (Gasterophilus spp.) migrate through the mouth and into the stomach, where they may cause ulcers or abscesses. Fall (following the first freeze) is the best time to treat for bots, as the larvae are in the stomach and can be killed all at once.
Large strongyles or bloodworms (Strongylus spp. and Triodontophorus spp.) disrupt blood flow to the intestines, which can result in colic. They can also cause anemia and brain damage.
Roundworms or ascarids (Parascaris equorum) mainly affect young horses (less than 2 years old). They can cause pneumonia (migrate through the lungs), intestinal obstruction, colic, and poor growth.
Pinworms (Oxyruis equi ) irritate the underside of the horse's tail and rectum, causing tail rubbing, tail hair loss, and weight loss.
Hairworms (Trichostrongylus axei ) can cause watery diarrhea. They live in the horse's stomach and small intestine.
Stomach worms (Habronema muscae) live in the horse's stomach lining, causing gastric abscesses or ulcerations.
Tapeworms (Anoplocephala perfoliata and Anoplocephala magna) live at the junction of the small and large intestines. Tapeworm infestation can cause colic, weight loss, and intestinal obstruction.
Transmission: The internal nematode parasite life cycle starts in the pasture, where parasite eggs are shed in the horse's feces. Infective larvae migrate out of the feces and onto nearby grass, where they are swallowed by a grazing horse. The larvae develop in several stages. Depending on the species, they may migrate throughout the body, damaging the stomach, intestines, blood vessels, liver, and lungs. Nematode parasites eventually reach the intestine, where they reach adulthood and begin producing eggs, which are deposited back into the pasture—starting the worm cycle all over again. Bots develop into flies, which then deposit their eggs directly on the horse's body, and the eggs are ingested when the horse grooms itself.
Clinical Signs: Diarrhea, weight loss, poor growth, colic, coughing, loss of appetite, a pot belly appearance, rough hair coat, tail rubbing, and diarrhea. |