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Short answers
to common
 What causes Johne's disease? What are the signs of Johne's disease and how can I tell if my herd has Johne's disease? How common is Johne's disease? What causes the signs of Johne's disease? 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? How do you control Johne's disease in a herd? Can Johne's disease be cured with antibiotics? Is there a vaccine for Johne's disease? Can humans get Johne's disease? Are there special laws or regulations regarding Johne's disease?
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 Johne's
(pronounced "Yo-nees") disease is a contagious bacterial disease of the intestinal
tract. A German veterinarian first described the disease in a dairy cow in 1895;
his name is used as the common name for the disease. The disease is also called
paratuberculosis because the bacterial cause of the disease is M. paratuberculosis.
Visit the history page for detailed
information.
Johne's
disease occurs in a wide variety of animals, but most often in ruminants. Ruminants
are hoofed mammals that chew their cud and have a four-chambered stomach. Some
of the more common ruminants are: cattle, sheep, goats, deer, antelope, and bison.
Johne's disease has been reported in all of these animals but is most commonly
seen in dairy cattle.
 The
bacterium that causes Johne's disease is named Mycobacterium paratuberculosis
often the name is abbreviated M. paratuberculosis. Microbial taxonomists
have suggested it should be renamed M. avium subsp. paratuberculosis,
and some publications use this name and abbreviate it MAP. It is a relative of
the bacterium that causes tuberculosis in humans and animals. M. paratuberculosis
only grows in animals: it can not grow and multiply in nature. However,
if soil or water is contaminated with this bacterium, it can survive there over
a year because of its resistance to heat, cold and drying. See the biology
of M. paratuberculosis for more information.
 Animals
infected with M. paratuberculosis usually develop diarrhea and rapidly
lose weight like the Limousin bull shown here. In general, Johne's disease is
a wasting disease of animals that continue to eat well. Infected animals appear
unthrifty, are often weak, but they do not generally have a fever. The signs of
Johne's disease can be confused the signs with intestinal parasites ("worms").
Because of the slowly progressive nature of the infection, signs of Johne's disease
are usually not seen until animals are adults. Signs tend to start within a few
weeks after calving but could happen anytime in the cow's reproduction cycle.
 A
1997 national survey of U.S. cow-calf operations (called beef suckler herds in
many parts of the world) estimated that 92.2% of beef producers were either unaware
of Johne's disease or only recognized the disease name, and that 7.9% of herds
were infected. The full survey report can be found at:
http://www.aphis.usda.gov/vs/ceah/cahm/Beef_Cow-Calf/bf97john.htm
No other countries have yet reported surveys to estimate the prevalence of Johne's
disease in beef cattle populations, however, anecdotal information and opinion
among experts suggests the situation is similar in many other countries.
 M.
paratuberculosis infects the part of the small intestine called the ileum.
There it causes a certain type of inflammation called granulomatous inflammation.
This inflammation thickens the intestinal wall, preventing it from functioning
normally. This leads to diarrhea and poor absorption of nutrients. As a result,
even though infected animals seem to be feeling and eating well, they will rapidly
lose weight.
 There
are three common ways to test animals for Johne's disease: culture of fecal samples,
DNA probe on fecal samples, and blood tests for antibodies to M. paratuberculosis.
Culture of the M. paratuberculosis from fecal samples — 
All animals can be tested for Johne's disease by doing a bacterial culture (growing
the bacteria in a test tube) of a fecal (manure) sample. Your veterinarian can
help collect and submit samples for a Johne's fecal culture. This test takes 8
to 16 weeks because of the extremely slow growth rate of M. paratuberculosis
and typically costs US$15 to US$35 per sample.
DNA probe on fecal samples. — M. paratuberculosis bacteria can be detected in fecal samples by use of sophisticated DNA probe tests. DNA probes are much faster than culturing the organism and can be done within three days because they do not require growth of the bacteria but instead detect its DNA. Unfortunately, DNA probe tests are not yet as sensitive as culture and are only able to detect infected animals when their infection has progressed to the stage where relatively large numbers of M. paratuberculosis are being excreted in the feces. Therefore, animals in early stages of the infection are not detected. The other disadvantage of the DNA probe for Johne's disease is that it is expensive to run, costing roughly US$35 per sample (although the price charged may be lower in states that subsidize testing through their veterinary diagnostic laboratory). Blood tests for antibodies to M. paratuberculosis — There are several blood tests for Johne's disease. The ELISA is the one considered most accurate and best standardized. Three ELISA-based tests are licensed by the U.S. Dept. of Agriculture for detection of M. paratuberculosis-infected cattle. These, as well as other ELISA tests, are available in other countries. The ELISA is fast, simple, inexpensive (US$8 to US$10 per animal) and able to detect animals that are infected before they show signs of Johne's disease. Many veterinary diagnostic laboratories offer the ELISA for Johne's disease. Products that can be used "cow-side" have recently entered the market but thorough independent evaluations have not yet been done. To learn more about diagnostic products from sponsors of this website, click here.
Control of Johne's disease herds is not difficult, but it does take patience and
consistency. In principle, two strategies must be employed at the same time; 1)
environmental situations that are conducive to infection transmission must be
avoided, and 2) adult animals carrying the M. paratuberculosis infection
must be identified by laboratory tests and removed from the herd.
For beef cattle this means:
Detailed information can be found under the control topic and in articles, available on this site.
Johne's disease is not curable (in practical terms for food producing animals). Although never reported, if it can be cured it would likely require use of multiple expensive antibiotics administered for a year or longer. For most animals, this is cost prohibitive. For detailed information visit the page on Antimicrobial Therapy.
 The
killed vaccine used in the U.S. and The Netherlands has been most studied. Results
indicate that, when given to calves less than 30 days old, it will enhance immunity
and decrease the rate of clinical Johne's disease (only studied in dairy herds).
However, it does not prevent infection of cattle with M. paratuberculosis
and can cause large injection site granulomas. While it may be helpful in control
of Johne's disease for some heavily infected herds, it is should not be used on
an industry-wide basis. This is a complex and controversial subject and the reader
is referred to sections of this website concerning control
of Johne's disease in dairy cattle for a more in-depth discussion of vaccines.
This is a very controversial subject. There is a human disease called Crohn's disease that resembles Johne's disease (clinical signs and pathology). Crohn's disease most commonly affects people 15 to 30 years old. It is a chronic diarrheal disease that has no known cause and no known cure. Recent reports in the medical literature indicate that 25 to 75% of patients with Crohn's disease test positive for M. paratuberculosis. A few laboratories have grown M. paratuberculosis from a few Crohn's patient specimens. However, no connection has been proven between contact with animals with Johne's disease or beef consumption and Crohn's disease. A detailed discussion of this topic can be found on the Zoonotic Potential page of this website.
Many states in the U.S. and also other countries are developing state or national programs to help control this disease. Many laws targeted at dairy cattle also include beef cattle. In the U.S., all cattle that test positive for Johne's disease by fecal culture (or comparable organism detection-based tests such as the DNA probe) can only move between states if they are going to slaughter. Take a look at the "Laws and Regulations" page of this website for more information. You should consult the veterinary official in charge of your area to learn about new or proposed regulations. Programs are being developed by other countries or states in the U.S. can be found through the Links page of this website. |
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