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Short
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What
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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. This website has information specific to each of the animals Johne's disease is most common in. Chose the animal under "area of interest" on the left.
A 1996 national survey in the U.S. estimated that 22% of U.S. dairy herds are infected. The full survey report can be found at: http://www.aphis.usda.gov/vs/ceah/cahm/Dairy_Cattle/johnsart.htm The U.S. rate of dairy herd infection is similar to that reported in other countries using similar tests: Netherlands (55%), Belgium (22%), Austria (7%), England and Wales (17%), Denmark (47%), New Zealand (60%) and the state of Victoria in Australia (22%). The herd infection rate in U.S. beef cattle is lower although not many surveys have been reported. A 1997 survey in the U.S. found that: 7.8% of beef herds were infected using the same survey methods as for dairy cattle. Infection rates in beef cattle a most likely lower than in dairy cattle due to differences in animal husbandry practices.
Johne's disease typically enters a herd of animals when an infected, but healthy-looking, animal is bought. The infection then spreads to other animals without the owner's knowledge. Eventually, often after several years, the owner recognizes signs of the disease in a number of animals. Individual animals get infected most often when they are calves less than 6 months old. They get infected by consuming milk, water, or feed contaminated with M. paratuberculosis. Young calves are far more susceptible to infection than are adults. Ingestion of the bacterium occurs when the newborn's environment is contaminated with manure from an infected animal, or by drinking milk from an infected animal. Feeding waste milk to calves is most responsible for spread of Johne's disease in dairy herds. After infection, many months or years go by until the infected animals shows signs of Johne's disease.
The best way to avoid this chronic infectious disease is to be as certain as possible that replacement cattle brought into the herd are not infected with M. paratuberculosis. This is not always easy but laboratory tests for Johne's disease in cattle have improved dramatically in recent years and are widely available. When using laboratory tests for pre-purchase screening of animals, it is important to understand that tests done on individual animals are not very sensitive, meaning they can't detect all infected animals. A way to get around this problem is to rely on tests done on the herd of animals from which you want to buy replacements. If a whole herd test is 100% negative, then the probability the herd is free of M. paratuberculosis infection is very high. Johne's disease test-negative herds are the best sources of animals for purchase. See the prevention topic for more information. Read more about preventing Johne's disease in the articles on biosecurity in the Articles and Brochures section of this website.
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.
DNA probe
on fecal samples — Blood tests
for antibodies to M. paratuberculosis — To learn more about diagnostic products from sponsors of this website, click here.
Control of Johne's disease in dairy herds is not difficult, but it does take patience and consistency. In principle, two strategies must be employed at the same time; 1) newborn animals must be protected from infection by being born and raised in a clean environment and fed milk free of M. paratuberculosis, and 2) adult animals carrying the M. paratuberculosis infection must be identified by laboratory tests and removed from the herd. For dairy cattle this means:
For more about calf raising, download the publication called "Raising calves - The 5 Cs of a healthy start" produced by the Wisconsin Milk Marketing Board. This brochure and other helpful articles on Johne's disease can be found on the Articles and Brochures page of this website. To learn more about calf feeding products from sponsors of this website, click here.
Johne's disease is not curable in practical terms. 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 more detailed information visit the page on "Antimicrobial Therapy".
This is a very controversial subject. There is a human disease called Crohn's disease that resembles Johne's disease. 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 shown between contact with animals with Johne's disease or milk consumption and Crohn's disease. A detailed discussion of this topic can be found on the "Zoonotic Potential" page of this website.
Given the present lack of knowledge about whether M. paratuberculosis can infect humans, it is better to be safe and not drink raw milk from infected herds. It should be noted that drinking raw milk is generally discouraged for many reasons other than presence of Johne's disease in a herd.
Many
states in the U.S. and also other countries are developing state
or national programs to help control this infection. You should
consult the veterinary official in charge of your area to learn
about new or proposed regulations. Websites outlining programs in
the U.S. states of Wisconsin and Minnesota as well as a model U.S.
herd certification-like program are listed on the Links
page of this website. Internationally the Australian animal industries
have the most well developed and well funded programs. A link to
their website is also listed on the Links
page. |
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