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Key takeaways

Tyzzer’s disease in horses is a severe form of hepatitis, caused by the bacteria Clostridium piliforme.

  • This bacterium mainly targets the liver in horses and in rare cases the intestines and heart
  • The main symptoms are related to the resulting liver failure; yellowed gums and eyes, lethargy, reduced appetite, fever, and seizures
  • Tyzzer’s is highly fatal and the prognosis is grave
  • Younger foals often die before any symptoms are present
  • Asymptomatic cases are common
  • Diagnosis is presumptive and based on clinical signs -Diagnosis is confirmed with bloodwork, diagnostic imaging, and liver biopsies
  • Successful treatment of tyzzer’s is rare, and focuses on supportive care
  • Preventative measures such as adequate colostrum intake, are important
  • Tyzzer’s is not highly contagious, but when there is one case, others are likely to arise throughout the year
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A closer look: Tyzzer’s Disease in Horses

Tyzzer's disease is an emergency, and although it is very rare, putting preventative measures in place is recommended. Tyzzer’s is a highly fatal disease for foals, usually affecting those between 5 days and 6 weeks old.

Risk factors

Tyzzer’s may also result in coma.

Adults, although potential carries for the bacteria, are immune. Higher occurrences of Tyzzer’s have been observed during high rainfall months in the spring, particularly April to June.

Possible causes

Tyzzer’s is caused by the bacteria Clostridium piliforme. It is most commonly ingested from the feces of adult nursing mares, but is present in the environment as well.

Main symptoms

Testing and diagnosis

Early diagnosis is vital considering the severity of Tyzzer’s disease. Diagnostic procedures include a physical examination, bloodwork, biopsy of the liver, and diagnostic imaging such as ultrasound and X-rays.

Steps to Recovery

There have been very few cases where treatment has been effective, and in these cases it was achieved with aggressive supportive care. This includes: IV fluids, parenteral nutrition, antibiotics, antimicrobials, anti-inflammatories, and anti-seizure medication. Due to the low success rate of treatment, it is suggested to focus on prevention.

Farms that have a case of Tyzzer’s disease often have sporadic cases every year, and close monitoring of foals is recommended.

Symptoms of Tyzzer’s disease appear between 4-7 days and last between 2 hours and 2 days past onset, but it is commonly asymptomatic. Treatment has not been found to be effective in most cases and many foals die within 24 hours, resulting in a grave prognosis.


As Clostridium piliforme is present in the environment as well as in the intestines of adults, it is difficult to avoid infection. At room temperature bacteria spores can live longer than a year in soiled bedding, so regular cleaning is suggested.

Prevention consists of ensuring that foals receive enough high quality colostrum and reducing factors that increase stress or immunosuppression. Factors that cause stress include overcrowding, poor sanitation, shipping, and capture. It is also recommended to maintain a high quality diet for nursing mares and foals, and to reduce compounds in the diet that are high in protein and nitrogen such as legumes or soybean meal.

Tyzzer's disease is not highly contagious, although presence of the bacteria and common predisposing factors affect all foals in an environment.

Tyzzer’s also affects a number of different species including other domestic animals such as cats, dogs, calves, rabbits, rats, and some birds.

Is Tyzzer’s Disease in Horses common?

Tyzzer's disease is very rare in horses.

Typical Treatment

Supportive care which includes:

  • IV fluids
  • Parenteral nutrition
  • Antibiotics
  • Antimicrobials
  • Anti-inflammatories
  • Anti-seizure medication


Francisco Uzal , DVM, MSc, PhD, DACVP - Writing for Merck Veterinary Manual
Thomas W. Swerczek - Writing for The Canadian Veterinary Journal
Equine Disease Quarterly - Writing for The Horse

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