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Answers to frequently asked questions. (Updated March 2010) For more detail, choose species and topic of interest in the column at the left.
What is Johne's disease and what causes it?
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What is Johne's disease and what causes it?
Johne's (pronounced "Yoh-nees") disease and paratuberculosis are two names for the same animal disease. Named after a German veterinarian*, this fatal gastrointestinal disease was first clearly described in a dairy cow in 1895.
A bacterium named Mycobacterium avium ss. paratuberculosis (let’s abbreviate that long name to “MAP”) causes Johne’s disease. The infection happens in the first few months of a goat’s life but the animal may stay healthy for a very long time. Symptoms of disease may not show up for many months to years later. This infection is contagious, which means it can spread from one goat to another, and from one species to another (cows to goats, goats to sheep, etc.)
MAP is hardy - while it cannot replicate outside of an infected animal, it is resistant to heat, cold and drying. See "Biology of M. avium ss. paratuberculosis" for more information about this bacterial pathogen.
(*Dr. Heinrich Albert Johne; follow the paths taken by scientists to understand Johne’s disease on the History page)
Johne's disease is primarily a health problem for ruminant species (ruminants are hoofed mammals that chew their cud and have a 3-4 chambered stomach) and occurs most frequently in domestic agriculture herds. Some of the more common ruminants are cattle, sheep, goats, deer, and bison. It is particularly common in dairy cattle, not because they are more susceptible to infection but because they are more frequently exposed to the organism that causes Johne’s disease (MAP).
Both domestic and non-domestic, free-ranging and captive infected ruminants have been reported from all parts of the world.
Non-ruminant wildlife such as omnivores or carnivores (birds, raccoons, fox, mice, etc.) may become infected, but rarely do they become sick due to the MAP infection. They are considered what is called a “dead end host”, meaning that the infection is not believed to spread further from them. (See Wildlife Epidemiology for an exception. http://johnes.org/wildlife/epidemiology.html)
For more information about a particular species, look at the column at the left: choose the animal under "area of interest" and select a specific topic of interest.
What are the symptoms of Johne's disease and what causes them?
There really are only two clinical signs of Johne’s disease: rapid weight loss and diarrhea. In some ruminant species, diarrhea may not be common. The infection occurs in calves/fawns/kids in the first months of life, but signs of disease usually do not appear until the animals are adults. Despite continuing to eat well, adult ruminants become emaciated and weak. Since the signs of Johne's disease are similar to those for several other diseases, laboratory tests are needed to confirm a diagnosis. If a case of Johne’s disease occurs, it is very likely that there are other infected herdmates (who may still appear healthy).
No one yet understands what causes a clinically normal animal that has been infected by MAP for months or years to suddenly become sick from the infection. We do know that at some point the MAP that have been lying quiet within cells of the last section 
of the small intestine (called the ileum) start to replicate and take over more and more of the tissue. The animal’s immune system responds to all these organisms with what is called granulomatous inflammation. This inflammation thickens the intestinal wall, preventing it from functioning normally. This, among other factors, means the animal cannot absorb the nutrition it needs and thus begins to lose body condition and diarrhea may occur. In effect, an animal with Johne’s disease is starving in spite of having a good appetite and eating well. The symptoms of Johne’s disease in cervid (deer) species have appeared in younger animals (yearlings) than what is commonly seen in other ruminant species.
As noted above, while the organism or its DNA may be detected in non-ruminant wildlife, disease may not occur. Few non-ruminant species seem to be made clinically ill due to MAP infection according to research to date.
How common is Johne's disease in ruminant wildlife?
Every country that has tested their ruminant domestic agriculture species for Johne’s disease has found cases of infection. In the U.S. it is estimated that 8% of the beef herds and 68% of the cattle dairy herds contain at least one animal infected with MAP. The infection has been found in a number of zoo collections as well.
The infection is much more prevalent in captive than in free-ranging ruminants, likely due to the greater concentration and exposure to MAP in a high animal density environment. Cases of both infection and disease in free-ranging or captive ruminants have occurred in all parts of the world and in all types of ruminant species ranging from axis deer to zebu.
How do wildlife species get infected?
In the majority of cases, a susceptible ruminant (less than 6 months old) must repeatedly swallow MAP to have a chance of becoming infected. Calves/kids/fawns swallow the organism if their grass, milk or water is contaminated with MAP. (If the dam herself is infected, she may have infected her offspring even before it is born or, in the advanced stages of the infection, the bacterium is shed directly into the milk.) Wildlife sharing range with infected domestic species or grazing pastures fertilized with contaminated manure from infected cattle or small ruminants risk infection of their newborns.
How can you protect wildlife from MAP infection?
MAP is a hardy organism, resistant to heat, cold and drying in the environment. A few studies show that it remains viable longer in shaded vs. partially shaded soil, and even longer in water and water sediment such as is found in troughs. While more than 90% of the organism s on a contaminated premise is believed to die off within a few months, a low level may remain for more than a year. The ability of this residual MAP population to cause new cases of infection is not known, but should be considered a risk for young animals grazing the premises. Feeding stations should be moved regularly to minimize manure contamination.
Limiting the exposure of wildlife to contaminated range and contaminated water is an important approach, as is preventing the spread of manure that might be grazed by these populations. This is particularly true in the months before the calving/lambing/kidding season.
How
do you test wildlife for Johne's disease?
New approaches are now available for testing that are cheaper and more reliable than ever before. The two common ways to test the adult animals in a herd for Johne's disease are:
- culture of fecal samples (individual or pooled; collected directly from the adult animal or the pasture) to isolate MAP or direct PCR with the same type of samples to detect MAP DNA,
- tests on blood samples for antibodies made by adult animals in response to MAP infection. (Although the effectiveness of serologic testing will vary by wildlife species since few assays are validated for them.)
You may also contact our veterinary staff via this website’s Ask An Expert feature if you still have questions after reviewing all the information on this website.
Click here to download a sample submission form.
Can Johne's disease be cured with antibiotics?
Can humans get Johne's disease?
The term “Johne’s disease” is used only to describe the clinical illness in ruminants that occurs after MAP infection.
There is a human ailment however called “Crohn's disease” that in several ways resembles Johne's disease. Crohn’s disease is a chronic inflammatory bowel disease (IBD) that has no known cause and no known cure. In some studies MAP has been found in tissues of Crohn’s disease patients more often than controls. Some researchers believe MAP contributes to Crohn's disease for at least a subset of patients. The majority of gastroenterologists, however, do not; they believe that MAP, if found in this subset of patients, is simply a by-stander amongst the many other organisms that are found in a malfunctioning gastrointestinal tract. No connection has been shown between contact with animals with Johne's disease, dairy product or meat consumption and Crohn's disease. This aspect of MAP is a complex and controversial area of scientific investigation. A detailed discussion of this topic can be found on the "Zoonotic Potential" page of this website.
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