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What is Tyzzer's Disease?

Tyzzer’s disease is an often fatal disease affecting young foals worldwide. This devastating disease, a type of hepatitis, is caused by Clostridium piliforme (C. piliforme), a spore-forming bacterium found both in wild and domestic animals. Though C. piliforme is thought to be relatively common in young horses, little is understood about its mechanisms. Research has been unfortunately limited due to challenges with its culturing. One leading theory, however, is that foals acquire the bacterium through oral exposure to invective spores, which likely emanate from the feces of both infected and carrier animals.

In addition to oral-fecal exposure, foals may possibly become infected while in utero from an asymptomatic mare. Contaminated soil may also be another source of infection due to the presence of bacteria in the waste. Another source of infection may stem from the relationship between a neonate and the nursing mare, particularly if the foal is born in the spring. During this time of year, a nursing mare has plenty of access to a high-fiber, nutrient-rich diet, which may lead to a proliferation of C. piliforme within her system. As the foal consumes the feces of the dam in order to establish a balance of intestinal flora, large amounts of C. piliforme flood the foal’s immature system, inciting infectious activity in the lower intestine, and possibly predisposing the horse for Tyzzer’s.  

Some of these foals die within mere days of disease contraction and are often found in a coma or dead by their caretakers. C. piliforme typically attacks the epithelial and smooth muscle cells of the small intestine, as well as hepatocytes (cells in the liver), and muscle cells in the heart. Tyzzer’s disease is one cause of liver failure in horses and foals. Since its path is so aggressive and invasive, is no wonder that Tyzzer’s disease is almost always fatal.

Locations where the disease has been reported in the United States include Connecticut, Idaho, Iowa, Maryland, Michigan, Montana and Wyoming. Cases are also widespread in Canada.

Tyzzer’s disease in horses is an often fatal disease caused by Clostridium piliforme (C. piliforme), a spore-forming bacterium.

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Symptoms of Tyzzer's Disease in Horses

  • Diarrhea
  • Depression
  • Emaciation
  • Ruffled coat
  • Melena
  • Depression
  • Lethargy
  • Hemorrhaging in lower intestine and abdomen
  • Convulsions
  • Coma
  • Death

Causes of Tyzzer's Disease in Horses

Clostridium piliforme bacterium spreads through oral-fecal exposure and possibly through contaminated soil. Regular cleaning of bedding and the living environment is most helpful as animals ingest bacterial spores from contaminated bedding, the environment, and feed. 

Two factors that appear to increase instances of Tyzzer’s disease are immunosuppression and stress. In addition to being infected by the mare, horses most predisposed to the disease are those under various stressors (shipping, changing environments, poor sanitation and overcrowding), those immunosuppressed, those on immunosuppressive drugs or sulfonamide, and those who were fed high-protein diets.

Diagnosis of Tyzzer's Disease in Horses

The onset of Tyzzer’s disease is as rapid and sudden as its progression. Infected foals usually succumb to liver failure between one and eight weeks of age, with most dying by week two. Once the horse shows signs of illness, the disease advances far too quickly for veterinary care to be effective. The most reliable indicator of this disease are the grayish, yellow necrotic lesions found on the liver of diseased animals. 

For some reason, other horses have antibodies for C. piliforme, and remain asymptomatic. 

Most horses are physically examined in a post-mortem condition. Foals sick with Tyzzer’s are usually found unresponsive or dead. The veterinarian conducts blood testing, as well as a fecal examination to test for C. piliforme.  Clinical signs are also observed.

Treatment of Tyzzer's Disease in Horses

Most foals do not survive Tyzzer’s disease, but from time to time a foal has improved. Veterinarians were puzzled, and tried courses of antibiotics to see if the bacterium responded positively or negatively. C. piliforme responded to tetracycline and somewhat to erythromycin and penicillin. Foals suspected of infection were given IV therapy with dextrose and other fluids. Some of these foals initially responded to treatment, but died soon after.

Recovery of Tyzzer's Disease in Horses

To best stave off infectious diseases, horse owners must be vigilant about maintaining quality soil and sanitary and safe environments for livestock. If disease has occurred in the surrounding area, restrain mares from eating such high-protein diets. Stressors that impact the health of any animal should be taken seriously and monitored for severity. Managing the number of bacterial spores within wild and domestic environments offers the best long-term solution for disease control. In addition to keeping bedding and feed clean, remove carcasses immediately.