Tyzzer's Disease

NWDC is in the process of updating this fact sheet. 

Other names: Hemorrhagic disease of muskrats, Errington’s disease


Tyzzer’s disease is caused by the bacteria Clostridium piliforme. It was first discovered in mice by Ernest Tyzzer in 1917. In 1946, Paul Errington described a similar disease (called Errington’s disease) in muskrats, though in 1971 it was determined that Tyzzer’s and Errington’s were in fact the same disease. Errington’s disease is now referred to as Tyzzer’s disease. 


Tyzzer’s disease is a significant disease of muskrats and rabbits that can cause major mortality events, particularly in young animals under stressful conditions.

Species Affected

Tyzzer’s disease primarily affects wild muskrats and cottontail rabbits. Other wildlife species affected by this disease include raccoons, coyotes, gray foxes, certain birds, snow leopards, white-tailed deer, and the lesser panda. In Australia, this disease has been reported in wild bush tail and common ringtail possums, as well as several captive species. Laboratory and domestic species affected by this disease include rabbits, rats, cats, dogs, horses, 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. Muskrats with this disease have been found 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 disease is transmitted when animals ingest spores from an environment contaminated with the 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 from 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 a rough hair coat. Some animals do not become ill but become asymptomatic carriers that can transmit the disease. Clinical disease usually occurs in animals under stressful conditions. It appears that latent infections can become clinical disease when animals are stressed. For example, muskrats have developed Tyzzer’s disease following the stress of capture, and domestic dogs and raccoons have developed Tyzzer’s after their immune systems were weakened by canine distemper virus. The bacteria primarily infect the intestines with subsequent distribution through the blood to the liver and heart. 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 diagnosed by isolating the bacteria in affected tissues (liver and intestines).


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


When Tyzzer’s disease outbreaks occur in wild muskrats, infected lodges and animal carcasses should be removed to eliminate the source of infection. 

Suggested Reading