Other Common Diseases

By R.D. Scoggins.

Clostridial diseases as a group are due to a family of bacteria that grow in the gut or tissue and produce gas and very powerful toxins that affect the nervous system.

Tetanus, a frequently seen disease of horses, is caused by a neuro-toxin produced by Clostridium tetani. This nerve tissue poison causes spasms and rigidity of the skeletal muscles. Affected horses cannot eat and have difficulty drinking, thus the term lockjaw. Over half of affected horses die due to suffocation, starvation or dehydration.

Due to the large number of Clostridium tetani in the horse's digestive tract, people working around horses should consult their physicians concerning tetanus immunization for themselves.

Infected horses acquire the problem through puncture wounds or other deep wounds. Within 10 to 14 days following injury, horses become increasingly nervous, then stiff or rigid and as a result have difficulty moving. The more rapid and severe the onset of symptoms, the less chance of recovery.

Persistent treatment and much nursing care are needed. Affected horses need to be protected from light and sound that can stimulate nervousness. Horses are placed in darkened stalls and their ears plugged with cotton to reduce stimuli from sound.

Veterinarians usually administer tetanus antitoxin, antibiotics, and sedatives repeatedly for several weeks. One third to one half of affected horses may recover if diagnosed early and treated vigorously.

Prevention is twofold. Unvaccinated animals should receive tetanus antitoxin within 24 hours following injury or surgery. This provides temporary protection for 10 to 14 days. If healing is not complete at that time, then tetanus antitoxin should be repeated at 2-week intervals until healing is complete.

Vaccination with tetanus tox6id provides a very stable immunity. All horses should be vaccinated against tetanus and receive annual boosters on a regular basis and following an injury.

Botulism: Two Types

Botulism is due to Clostridium botulinium and can occur in adults as "forage poisoning" or in foals as the Shaker Foal Syndrome.

With "forage poisoning", adult horses become weak and stagger, have difficulty swallowing, and may go down and be partially or completely paralyzed. Silage, incompletely cured hay, or forage with spoiled areas are usually the cause. A commercial vaccine is not available at present. Prevention is best accomplished by careful selection of hay, silage or other harvested forage for horses.

The Shaker Foal Syndrome appears as a problem in young foals nursing mares being fed high energy, high protein diets. Experimental vaccination of pregnant mares prior to foaling has prevented the condition, and vaccine may become available commercially.

Care in nutritional management of mares nursing foals may control or prevent Shaker foals from developing. Affected foals become uncoordinated, develop jerky movements, and eventually become paralyzed and die. Once symptoms are apparent, treatment has little effect in improving the foal's condition.

Clostridial Myositis

Infections of muscle masses by one or more of several clostridial bacteria families can occur. These organisms usually enter through wounds, needle injections, or other muscle injury.

The bacteria grow rapidly, form gas pockets, create severe pain, and cause shock from the toxins produced. Hand pressure causes both crackling sounds and sensation due to the gas formed under the skin. Often, cattle are or have been present when a problem occurs.

Veterinarians treat this condition by promptly establishing drainage and using adequate dosages of appropriate antibiotics. Despite vigorous treatment, some cases fail to respond.

Appropriate injection techniques, avoiding the use of irritating drugs, and not injecting excessive volumes at one site are all important in preventing clostridia) myositis. Prevention of injuries and prompt attention to any wound are helpful in preventing this disease. No approved vaccines are available.

Sleeping Sickness

Three forms of this disease are caused by viruses that affect the nervous system. Wild animals and birds act as reservoirs; the viruses also can affect humans. With the Eastern and Western forms, horses are dead-end hosts and the virus does not spread from them.

Venezuelan encephalitis spreads between horses and from horses to humans. Mosquitoes are the principal means of virus transmission between victims. Thus horses at pasture are more susceptible than stabled horses.

Infected horses initially develop a fever, act as though they have problems seeing, wander aimlessly, stagger, grind their teeth, and have a drooping lip. The disease may progress until paralysis occurs. Mild cases recover slowly over several weeks.

From 25 to 50 percent of those infected with the Western form may die, over 90 percent of those infected with the Eastern form die, and 75 percent die with the Venezuelan virus.

No specific treatment is available, but veterinarians can provide supportive care. Mosquito control is an important preventive measure, as is annual vaccination. The Venezuelan form has not been a problem in the United States since 1971, but could enter this country from Latin America.

Highly effective vaccines are commercially available and should be administered annually, before the mosquito season. They may be combined with other vaccines as well.

Swamp Fever

Equine Infectious Anemia (EIA) or swamp fever is a viral disease. In the acute form, it causes severe red blood cell destruction and resultant anemia. An inapparent carrier state occurs upon recovery. The virus is spread by bloodsucking insects and repeated use of needles or instruments without adequate sterilization between patients.

The disease causes severe anemia, fever, weakness, weight loss, edema, and sometimes death. Inapparent infections show few if any symptoms. Horses with inapparent infections that receive regular hard physical work or some other stress frequently become clinically apparent cases.

Clinical diagnosis of EIA is by a positive "Coggins Test". Titers causing a positive test occur 2 to 4 weeks after the initial disease.

No effective treatment is available. Prevention is best accomplished by maintaining Coggins Test negative horses only where other negative tested horses are maintained. Fly control and use of disposable needles among horses is an important aspect of control. Any horse that has a positive Coggins test should be maintained away from uninfected horses, especially during the insect season.

Rabies

Rabies (Hydrophobia) is a universally fatal viral disease of the central nervous system of all mammals. The virus is transmitted in saliva and infects humans, as well as other mammals. Wild animals, especially raccoons and skunks, appear to be important reservoirs of the disease.

When horses come in contact with rabid wild animals, their curiosity often results in being bitten on the muzzle. Symptoms of rabies usually occur within 2 weeks following the bite.

A sudden change in behavior is the first indication of rabies. Drooling may or may not occur. After 1 to 3 days horses may suddenly become vicious, attempting to bite without provocation. Some roll extensively, as though with colic. The size and strength of horses makes them dangerous and potentially unmanageable. Self-mutilation is not uncommon.

Treatment is not considered effective nor feasible nor safe for the humans involved. Suspect animals should be confined for 2 weeks. If the horses are then destroyed, care should be taken not to damage the brain. Have a veterinarian remove the head and prepare it for submission to a laboratory for examination at once.

Horses may be protected against rabies by vaccination with an approved product properly administered by a licensed veterinarian.

R.D. Scoggins is Equine Extension Veterinarian, College of Veterinary Medicine, University of Illinois, Urbana-Champaign.