What is Johne’s disease?
Johne’s is a slow, progressive, contagious and untreatable bacterial disease that ordinarily infects calves but does not show clinical signs until animals are three or more years of age. Infected animals maintain a normal temperature but exhibit weight loss and diarrhea. In the later stages of the infection, animals can become weak. Some infected animals even die.
What causes Johne’s disease?
Johne’s disease is caused by Mycobaterium paratuberculosis. This bacterium is a relative of the bacterium that causes tuberculosis in humans (Mycobacterium tuberculosis), cattle (Mycobacterium bovis) and birds (Mycobacterium avium).
M. paratuberculosis can replicate only when it is in animals. It cannot multiply outside the animal in nature. But, if soil or water is contaminated with M. paratuberculosis, the bacterium can survive for more than a year because of its resistance to heat, cold and drying.
Why is Johne’s disease called Johne’s?
The bacteria known to cause Johne’s, Mycobacerium paratuberculosis, was first isolated in 1895 by Dr. Heinrich Albert Johne. Hence the name “Johne’s disease.”
What are the signs of Johne’s disease?
The two most common sign of M. paratuberculosis infection—Johne’s disease—are rapid weight loss and diarrhea (in cattle). Animals with Johne’s disease tend to waste away despite a healthy appetite.
Several weeks after the onset of diarrhea, a soft swelling may occur under the jaw (bottle jaw), and this condition 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 two or more years after the initial infection which usually occurs at birth.
Diagnosis of Johne’s should be confirmed by the use of laboratory tests. In fact, Johne’s disease can only be confirmed by use of laboratory tests since the signs of Johne’s disease can be confused with the signs of several other diseases.
What causes the signs of Johne’s disease?
Mycobacterium paratuberculosis infect the lower part of the small intestine known as the ileum and causes a granulomatous inflammation. This inflammation thickens the intestinal wall, preventing nutrient absorption and causing diarrhea. The result is weight loss despite animals appearing to be feeling well and having a healthy appetite.
What are the stages of Johne’s disease infection in cattle?
Johne’s disease has three stages. Stage I is a silent, subclinical and non-detectable infection seen typically in calves, heifers and young stock less than two years of age and in adult animals exposed to small doses of disease-carrying organism. Infected animals at this early stage are rarely detected with currently available diagnostic tests, including fecal culture or serologic tests (ELISA). This stage progresses slowly over many months or years to Stage II.
Stage II is subclinical infection that typically occurs in older heifers or adults. Animals at this stage appear healthy but are shedding adequate numbers of M. paratuberculosis organisms in their manure to be detected on fecal culture. Blood tests will detect some animals but not all animals at this stage. Blood test (ELISA) positive animals should be confirmed positive by fecal culture. These animals pose a major but often hidden threat for infection of other animals through contamination of the environment.
Stage III is clinical Johne’s disease which is any animal with advanced infection, the onset which is often associated with stress such as recent calving. Cattle at this stage have intermittent, watery pea-soup manure. Animals lose weight and gradually drop in milk production but continue to have a good appetite. Some animals appear to recover but often relapse in the next stress period. Most animals in Stage III are shedding billions of organisms and are positive on culture. Most are positive on serologic tests (ELISA and AGID). Clinical signs often last several weeks to months before the animals are sent to slaughter in a thin, emaciated condition.
In the final and terminal aspects of Stage III, animals become emaciated with fluid diarrhea and develop “bottle jaw.” The carcass may not pass meat inspection for human consumption in the later phases of Stage III.
How do animals get Johne’s disease?
Transmission of Johne’s disease occurs when healthy-looking but infected animals are introduced into a herd. And, once an infected animal is in a herd, the bacteria can be quickly spread to its herdmates via the infected animal’s feces.
How is M. paratuberculosis spread among herdmates?
Infected animals shed large numbers of bacteria in their feces, leading to contamination of feed and water sources. As a result, the most common method of infection is the ingestion of Mycobacterium paratuberculosis bacteria via manure-contaminated udders, milk, water or feed.
Infected animals can also shed the bacteria in their colostrum and milk, and infected dams can also pass the disease in utero on to their offspring.
Young animals 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 adult animal or when a young animal drinks milk from an infected animal. The milk may become contaminated from the environment—manure-stained teats—or, in the advanced stages of the infection, the bacterium is shed directly into the milk.
Research also shows that sub-clinically infected animals are a significant hazard of maintenance and spread of infection.
If a herd has one obvious clinical case of Johne’s disease, what is the likelihood of other animals being infected?
In the typical herd, for every animal in Stage III of Johne’s (where cattle have intermittent, watery pea-soup manure and are losing weight while having a healthy appetite), a herd owner can expect 10 to 15 cows in Stage I with subclinical and non-detectable Johne’s and 6 to 8 cows in Stage II with subclinical and shedding M. paratuberculosis organisms. In total, a herd with one obvious clinical case of Johne’s disease is likely to have 15 to 25 other animals infected. This is what the industry calls “the iceberg phenomenon.”
Can Johne’s disease be prevented?
The best way to avoid this chronic infectious disease is to be as certain as possible that animals brought into the herd are not infected with M. paratuberculosis. This is not always easy.
Can Johne’s be controlled?
Yes, management measures can be implemented and followed to help prevent and control Johne’s disease. That said, Johne's disease must be managed as a herd problem and not treated as an individual cow disease. Research shows that diagnosis of one clinically-infected animal in a herd of 100 lactating cows implies that at least 25 other animals are infected and less than eight of those can be detected by the tests currently available.
Basic prevention/control strategies include:
- Reduce newborns’ exposure to manure from adult animals by cleaning individual calving stalls between each calving and not allowing manure to build in any calving area.
- Avoid manure contamination of feed by using feed bunks and not using the same equipment to handle feed and move manure.
- Avoid manure contamination of water sources where animals drink.
- For natural colostrum needs of newborn animals, use colostrum from Johne’s-negative animals.
- Do not pool colostrum.
- Avoid natural nursing and milk feeding whenever possible. Feed an artificial milk replacer or pasteurized milk instead of raw milk to supply the needs of newborns. Never feed pooled milk or waste milk.
- Thoroughly clean the udder and teats before collection of the colostrum to avoid manure contamination.
- Identify and remove all test-positive animals. At minimum, keep these individuals separate.
- Cull or separate the offspring of infected dams as soon as possible.
- When purchasing herd additions, buy from low-risk herds.
Your veterinarian can help you develop a strategic plan for Johne’s prevention and control for your farm. To learn more, please go to “Quick Links” on this website and click on the “Handbook for Veterinarians and Dairy Producers’ or “Handbook for Veterinarians and Beef Producers.”
Consult with your veterinarian about which Johne’s test is best for your situation and use a test-certified diagnostic laboratory.
Can a herd be tested for Johne’s disease?
Yes. The past decade has resulted in the development and commercialization of multiple accurate and cost-effective diagnostic tests for M. paratuberculosis. The three common ways to test are culture of fecal samples, DNA probe on fecal samples and blood tests for antibodies to M. paratuberculosis. Your veterinarian can help you determine which test is best for your situation.
While some tests are simple enough to be done in a veterinary clinic or on the farm, most require sophisticated laboratory equipment and skilled laboratory technicians to perform. In addition, factors such as the amplitude of a test result (numerical value) and herd infection rate (prevalence) can influence interpretation of Johne's disease test results.
It is recommended testing be performed by a veterinarian and interpretation be made by a qualified diagnostic laboratory.
Which Johne’s test is best for my situation?
Testing is a veterinarian-producer decision. The “best test” will be determined by you and your veterinarian answering the question “What is the purpose of testing?”.
Testing purposes include:
- To classify herd as infected.
- To obtain a precise estimation of within herd prevalence.
- To control disease.
- For surveillance.
- To eradicate by wanting to eliminate M. paratuberculosis from the herd.
- To confirm a clinical diagnosis in a herd with no prior confirmed JD cases.
- To confirm a clinical diagnosis in a known M. paratuberculosis infected herd.
- To determine if a particular animal is Johne’s-free prior to purchase.
How do I get my herd certified as Johne’s free?
The first step to becoming a Johne’s-free or low-risk herd is to contact your veterinarian or state Designated Johne’s Coordinator. Your veterinarian or DJC will explain what it takes to achieve certification. To contact your DJC, click on State Contacts/Info.
Is Johne’s disease treatable?
Scientific review and a case study show that therapy for M. paratuberculosis in cattle produces only remission of clinical signs and does not eliminate the infection. In addition, therapy was costly, inconvenient since it requires daily medication and, once treatment stopped, the signs of the infection returned since the infection was not cured.
As such, producers should prevent introduction of M. paratuberculosis in their herds by purchasing low-risk animals and help control Johne’s disease by culling in-herd animals that have Johne’s and initiating strategies to help prevent and control Johne’s within their herds.
Can I learn more about Johne’s disease in the comfort of my home or office?
Two Johne’s courses are offered online: Online Producer Course and Online Johne’s Disease Veterinary Certificate Course.