Short answers to common questions. For more detail, choose a specific topic. What is Johne's disease and what wildlife species can get it? What causes Johne's disease? What are the signs of Johne's disease? How common is Johne's disease in wildlife? How do animals get Johne's disease? How can you prevent your animals from getting Johne's disease? How do you test animals for Johne's disease? Can Johne's disease be cured? Can humans get Johne's disease?		General Dairy Beef Goats Sheep Elk Bison Wildlife

What is Johne's disease and what wildlife species can get it?

Johne's (pronounced "Yo-nees") disease is a contagious, slowly developing and fatal bacterial disease of the intestinal tract. A German veterinarian first described it in a dairy cow in 1895 and the disease was named after him. The disease is also called paratuberculosis.

Johne's disease primarily occurs in domestic and wild ruminant species such as sheep, goats, cattle, bison, deer, llama, impala, oryx, etc. It has also infrequently been reported in non-ruminant species e.g. rabbits, primates, fox, stoat, badgers and raven.

What causes Johne's disease?

The bacterium that causes Johne's disease is named Mycobacterium avium subspecies paratuberculosis. The name is abbreviated M. a. paratuberculosis or M. paratuberculosis. It is in the same family as the bacterium that causes tuberculosis in humans and animals and the type of disease it causes shares some characteristics with tuberculosis: it is slow to develop, it is resistant to antibiotics and is contagious. M. paratuberculosis can replicate only when within the animal; it cannot multiply in the environment. However, the bacterium reportedly can survive, still infectious, in the soil or water for over a year because of its resistance to heat, cold and drying.

What are the signs of Johne's disease?

This infection is hard to detect. The antemortem signs of Johne’s disease are vague and months can pass after infection before they appear. In cattle, weight loss and diarrhea in an animal with a good appetite are common indications. Weight loss in animals with a good appetite may be the only indication in some species such as sheep, goats and perhaps non-domestic hoofstock species as diarrhea is not a common sign. The animal may appear unthrifty and its coat may be in poor condition. The signs of Johne's disease can be confused with the clinical indications of other conditions such as parasitism, OPP (ovine progressive pneumonia), CLA (caseous lymphadenitis) or malnutrition. Of course, more than one problem may be occurring - for example, a blesbok eventually succumbing to Johne’s disease improved clinically after treatment for parasites. Because of the slowly progressive nature of the infection, signs of Johne's disease are usually not seen until animals are adults.

The infection is easy to miss at necropsy as well. The gastrointestinal tract of cases in early stages of infection may look completely normal both grossly and microscopically. This means that you may not find evidence at necropsy that supports an antemortem (fecal culture isolation, high antibody) diagnosis. Animals from some species (sheep, bison) may present minimal signs of pathology even in later phases of infection.

How common is Johne's disease in wildlife?

Johne’s disease has been diagnosed in more than one-third of the captive wildlife collections in the United States. Zoos in other parts of the world have reported cases as well. The infection may be present in a greater number of zoos since more than a third of AAZV accredited facilities do not test for the infection (per 1999 data). The majority of the cases (72%) were found in non-domestic hoofstock.

The infection has also been detected in free-ranging wildlife (tule elk, key deer, bison, non-hoofstock: Beard,P.M. et al. Paratuberculosis infection of nonruminant wildlife in Scotland. 2001. J Clin.Microbiol. 39 (4) 1517-1521).

How do animals get Johne's disease?

Johne's disease typically enters a zoo exhibit when an apparently healthy, but infected, animal is introduced. This animal contaminates the premises (feed, ground, water) by shedding the organism in its manure. The organism is then ingested by other animals. Hoofstock less than 6 months of age are thought to be most susceptible to infection and their suckling manure-soiled teats is another route of infection. It is also possible that a dam in the later phases of the infection can shed M. paratuberculosis into her milk and colostrum, thus transmitting it to her offspring. For free-ranging wildlife, the most likely initial source of the infection is shared range with domestic agriculture species given the higher prevalence of Johne’s disease in the latter species.

How can you prevent your animals from getting Johne's disease?

The best way to avoid this chronic infectious disease is to be as certain as possible that animals brought into the exhibit are not infected with M. paratuberculosis. The best information you can obtain to estimate the risk of introducing an infected animal is the test results for the source group, not just the results for the individual animal. If you know that the animal comes from an exhibit that has been fecal-culture negative for M. paratuberculosis, your confidence is much higher than if all you have is negative test results for the individual animal. If it is not possible to obtain test results for the exhibit, at least test the dam of the animal to be introduced. This is especially important if you are planning to introduce a young animal since tests on animals less than one year old are not likely to be informative given the biology of Johne’s disease. (The young infected animal is not likely to be shedding the organism regularly in its manure, therefore the culture result will be negative nor will the animal be producing antibody, thus blood tests will be negative).

Following general rules of sanitation are helpful in blocking transmission of the infection. Feeders and waterers should be designed to minimize the likelihood of fecal contamination and manure should be removed from the exhibit regularly. Provide clean, dry areas for kidding/calving/lambing. Animals with weight loss or diarrhea should be segregated from exhibit-mates and tested by fecal culture.

How do you test wildlife for Johne's disease?

The recommended testing method for non-domestic hoofstock is culture of fecal samples. The biology of the disease can make it difficult to detect infected animals, especially those in an early stage of infection. A truly infected animal in this “sub-clinical” phase may not be shedding the organism consistently (thus the fecal culture may be negative). Since animals in later stages of the infection shed the organism more frequently and in greater numbers, the culture assay is more sensitive in clinically affected animals.

It is much more informative to know the test status of all adult animals sharing an exhibit than to have a single test result for one animal completed at the time of shipment. Group testing provides much higher confidence in the true infection status of each animal.

Blood tests for antibodies made in response to M. paratuberculosis infection are also available but their use has been validated in domestic hoofstock only (cattle, sheep, goats). Blood tests can be used to establish an index of suspicion in a herd of animals, but should not relied upon to establish a definitive diagnosis of Johne’s disease for an individual animal.

Recommended testing protocols

Can Johne's disease be cured?

Although few studies have been reported, Johne's disease is not considered a curable disease. As with most diseases caused by mycobacteria, the course of therapy is very long (months) and expensive. For most animals, treatment is cost prohibitive and the best that can be expected is an improvement in clinical signs while under treatment, not a cure.

Can humans get Johne's disease?

This is a very controversial subject. There is a human disease called Crohn's disease that in some ways resembles Johne's disease. The cause of this chronic inflammatory bowel disease is not known and there is no known cure. A few laboratories have grown M. paratuberculosis from a few Crohn's patients' specimens but there is no evidence that the organism caused the disease. No connection has been shown between contact with animals with Johne's disease or milk consumption and Crohn's disease.