Johne's Disease 



Johne's disease is a contagious, chronic, and usually fatal infection that affects 

 primarily the small intestine of ruminants. Johne s disease is caused by Mycobacterium 

 avium subspecies paratuberculosis (M. avium suhsp. paratuberculosis), a hardy 

 bacterium related to the agents of leprosy and TB. Johne's disease is found worldwide. 



About 41 percent of U.S. dairy herds have at least one cow that tests positive for 

 Johne's; infection is even more common in large dairy herds. Because few herds 

 have instituted biosecurity programs, infection continues to spread. Although 

 infection seems less widely distributed in beef herds, Johne's is nonetheless of critical 

 significance to all cattle producers. 



Johne's disease can have severe economic impacts on infected herds. It is imperative 

 that U.S. herds employ safeguards against becoming infected. Identifying and 

 protecting noninfected herds will provide a source of breeding stock and replacement 

 animals for other herds and help to reduce the national prevalence of the disease. 



Clinical Signs and Stages 



In cattle, signs of Johne's disease include weight loss and diarrhea with normal 

 appetite. Several weeks after the onset of diarrhea, a soft swelling may occur under 

 the jaw. This intermandibular edema, or "bottle jaw," is due to protein loss from the 

 bloodstream into the digestive tract. Animals at this stage of the disease will not live 

 very long — perhaps a few weeks at most. 



Signs are rarely evident until 2 or more years after the initial infection, which usually 

 occurs shortly after birth. Animals exposed at an older age, or exposed to a very small 

 dose of bacteria at a young age, are not likely to develop clinical disease until they are 

 much older than 2 years. 



Johne's disease is generally described as having four stages: 



Stage I: Silent, subclinical, nondetectable infection. Typically, this stage occurs 

 in calves, heifers, and young stock under 2 years of age or animals exposed at an 

 older age. Current tests (including fecal culture and serological tests) cannot detect 

 infection in animals that young. Research to develop new tests to detect the disease in 

 such animals is ongoing. This stage progresses slowly over many months or years to 

 Stage II. It is possible that some animals recover from this early phase of infection. 



Stage II: Subclinical shedders. This stage usually occurs in heifers or older animals. 

 Animals appear healthy but are shedding M. avium subsp. paratuberciilosis in their 

 manure at levels high enough to be detected. Current blood tests are not reliable to 

 detect Johne's in animals at this stage. These animals pose a major but often hidden 

 threat of infection to other animals through contamination of the environment. 

 Stage II animals may or may not progress over time to Stage III. 



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