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Tyzzer’s Disease

Other Names: Hemorrhagic disease of muskrats, Errington's disease


Tyzzer's disease is a disease of muskrats, rabbits, and laboratory animals caused by a bacteria called Clostridium piliforme. Tyzzer first described this disease in mice in 1917, and Errington described a similar disease (called Errington's disease) in muskrats in 1946. In 1971 it was determined that Tyzzer's and Errington's were in fact the same disease that is now referred to as Tyzzer's disease.


Tyzzer's disease is a significant disease of muskrats and rabbits that can cause major die-offs, particularly of young animals under stressful conditions.

Species Affected

Tyzzer's disease primarily affects wild muskrats and cottontail rabbits, though it has also been reported in free-living raccoons and captive coyotes and gray foxes. Tyzzer's can also affect birds, according to at least one report. In Australia, this disease has been reported in free-living bushtail and common ringtail possums, as well as several captive species. Laboratory and domestic species affected by this disease include rabbits, rats, cats, dogs, gerbils, hamsters, and rhesus monkeys. This disease is not considered a human health concern.


Tyzzer's disease has been reported in North America and Australia. The disease has been reported in muskrats in Connecticut, Maryland, Ohio, Iowa, Michigan, Idaho, Wisconsin, Wyoming, Montana, and Oregon in the United States, and Ontario, British Columbia, Saskatchewan, and Manitoba in Canada. Tyzzer's has also been reported in cottontail rabbits in Maryland. Outbreaks usually occur in the spring or fall. Tyzzer's has not been confirmed in Pennsylvania, though it has been suspected as an important mortality source for muskrats.


Tyzzer's disease is transmitted when animals ingest spores from an environment contaminated with feces of infected animals. The spores can remain infectious in the environment for at least 5 years.

Clinical Signs

Clinical signs are usually not observed because animals die quickly of Tyzzer's disease (muskrats may die within 5-10 days of spore ingestion). When clinical signs are observed they include diarrhea with or without blood, depression, loss of appetite, and rough hair coat. Some animals do not become ill but become asymptomatic carries that can transmit the disease. Clinical disease usually occurs in animals under stressful conditions, and it seems that latent infections can become clinical disease when animals are stressed. For example, muskrats have developed Tyzzer's disease following the stress of capture; also, domestic dogs and raccoons have developed Tyzzer's after their immune systems were weakened by canine distemper virus. The bacteria infect the intestines and the liver, so necropsy of animals that died of Tyzzer's often reveals ulcers and hemorrhage in the large intestine and small white-yellow spots on the liver.


Tyzzer's disease is usually diagnosed by visualizing the bacteria microscopically in affected tissues (liver and intestines).


Antibiotics can be used to treat laboratory and domestic animals, but treatment is usually not attempted in wildlife.

Suggested Reading

Michigan Department of Natural Resources. Wildlife Disease. Tyzzer's Disease.,1607,7-153-10370_12150_12220-27297--,00.html>

Wobeser, Gary. 2001. Tyzzer's Disease. Pages 510-513 in E. S. Williams and I. K. Barker, editors. Infectious diseases of wild mammals. Iowa State University Press, Ames, Iowa, USA.