Johne’s disease (pronounced “yo-nays”) is a contagious, chronic, and often fatal infectious disease, mainly attacking the small intestine of ruminants, such as cattle, sheep, and goats. Rigorous hygiene management practices are the best prevention available.
The bacteria that causes Johne’s disease is Mycobacterium avium subspecies paratuberculosis (also known as M. paratuberculosis or MAP). As its name suggests, it is present in cases of tuberculosis and leprosy. It may also cause Chron’s disease in humans.
German pathologist Heinrich Albert Johne first reported the disease in cattle in 1895.
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What Is Johne’s Disease
Also known as paratuberculosis, Johne’s disease (pronounced “yo-nays”) is a contagious, chronic, and often fatal infectious disease, mainly attacking the small intestine of ruminants, such as cattle, sheep, and goats. Johne’s disease is particularly prevalent as it affects all kinds of ruminants, not just bovine ones.
It is principally a wasting disease. Johne’s disease causes increasingly acute diarrhea and small intestine inflammation, meaning animals cannot effectively absorb or distribute nutrients from food.
How Is Johne’s Disease Spread?
Johne’s disease is usually acquired by the inadvertent ingestion of fecal matter by suckling calves. The source of infection is almost always via the mother’s udder and teats. The condition can pass from animal to animal via saliva.
Young animals can also contract the disease by ingesting contaminated milk or colustrum from an infected animal.
Colostrum is the very concentrated, golden-colored liquid a cow produces immediately after the birth of a newborn. The bioactive compounds found in colostrum are essential for health and growth.
Infected pregnant cows can pass on the disease to their calf while it is still in-utero.
Fecal shedding of the bacteria (spread of the disease through infected excrement) commences before any clinical signs are evident. “Silent carriers” (infected animals showing no signs of the disease) are familiar transmission sources.
Vulnerable To Bacterial Infection
A non-infected herd typically becomes exposed through new members or replacement cattle carrying the disease. Recently-born calves of less than a month are most vulnerable to bacterial infection and do not form an effective immune system until around one year of age.
Healthy adult cattle will only usually contract the disease if exposed to the bacteria for prolonged periods.
Johne’s disease is not a zoonosis. However, as mentioned, MAP, the organism responsible for Johne’s disease, has been found in Chron’s disease patients. Crohn’s disease resembles Johne’s disease in that it causes diarrhea and inflammation of the intestinal tract.
There is a difference in the frequency of clinical signs between beef and dairy calves. With dairy cattle, these signs do not commonly occur until ages 3 to 5. However, beef cattle show the signs only a few weeks after birth.
Common Signs and Symptoms
Clinical disease signs are not obvious, and there is no indication of loss of appetite after the initial infection. It can take two or more years after contracting the disease for symptoms to present themselves.
Once they do, weight loss is quick, and the infected animal becomes frail and emaciated. Johne’s disease symptoms are sometimes difficult to read correctly. This rapid weight loss occurs despite the infected cattle eating normally.
Further complicating the diagnosis is the lack of fever or any related symptoms. Consequently, it is essential to ensure any new animals have tested negative before allowing them to join your herd.
The organism attaches itself to the walls of the lower ileum (or small intestine) and causes chronic enteritis (inflammation of the intestine). The cow’s immune response is for the infected tissue to try and regenerate new, healthy tissue leading to a thickening of the intestinal walls.
These walls form lesions, leaking proteins and then losing the ability to absorb them.
Muscle Wastage and Low Milk Yields
As a result, cows exhibit muscle wastage and low milk yields. Swelling due to fluid retention may also form under the jaw and cause the condition known as “bottle jaw.” These symptoms progressively worsen, leading to weakness, malnutrition, and death.
In the later stages of infection, antibodies present themselves in the animal serum, indicating that clinical signs and death will soon follow.
Reports from the U.S. Department of Agriculture (USDA) suggest that eight percent of beef herds, and over 20 percent of dairy herds carry the disease.
These figures are questionable, and experts estimate the incidences are far higher. A 2007 National Animal Health Monitoring System study found that nearly 70 percent of U.S. herds had at least one cow that had tested positive for Johne’s.
Reports from farms in southwest England in 2006 stated that nearly 98% of dairy farms and 79% of beef farms had cattle that tested positive for Johne’s disease.
Johne’s disease has no known treatment, so the best way to keep outbreaks to a minimum involves excellent hygiene practices.
This includes screening procedures for new herd members to recognize and remove infected animals.
If an outbreak should occur, take the following steps:
- Most dairy farmers separate newly-born calves from their mothers a few days after birth. This practice will stop the spread of Johne’s disease as you will feed calves with a milk replacer or pasteurized milk instead of their mother’s raw milk
- MAP is resilient and very resistant to heat and cold. It can survive on grass for around a year if left untreated and even longer in water, although it struggles to reproduce. Carry out a tilling procedure, use non-replacement feeder cattle to clear the pasture, or let environmental conditions kill any microbes
- Isolate all females and keep them separate from the rest of the herd before carrying out testing
- Cull or separate calves from infected cows and heifers straightaway
Contact a veterinary expert to ascertain the stage and level of the herd infection. As mentioned, signs of Johne’s disease can be tough to detect until a significant time has passed. Veterinarians will be able to administer diagnostic tests on cattle and fecal cultures.
The veterinarian should then implement an effective disease control program and give sound herd management advice, depending on the test results.
Polymerase chain reaction (PCR) tests are an effective way to reveal shedding animals. These tests detect the pathogen’s DNA to a very high degree. Crucially, they also recognize cattle that have ingested bacteria but have not developed an infection (transiently infected).
The number of bacteria shed in productively infected cattle will typically tally with clinical signs.
Enzyme-linked immunosorbent assay (Elisa) tests, considered the most reliable form of immunoassay testing, can measure a cow’s immune response to M. paratuberculosis. The test can detect if the pathogen has entered the animal.
Control program results for Map infection are often challenging to quantify because cattle respond differently. The stage of the cow’s condition will often determine which kind of test she will receive.
The most effective and flexible herd monitoring method combines PCR and Elisa tests. You can decide whether you concentrate on testing new additions to the herd or individual animals already established.
PCR and Elisa testing is quicker – test results only take a few hours – than methods involving bacterial cultures.
A vaccine consisting of oil and dead mycobacteria is available in the U.S. but is only a preventative measure.
Lumps can appear after application near the injection site, usually the brisket. Occasionally, these lumps turn into abscess-like lesions. Although the vaccine is for calves less than 30 days old, these lesions may last for the remainder of the calf’s lifespan.
Another vaccine available outside the U.S. consists of live M. paratuberculosis, which cannot cause disease.
Vaccine efficacy is unclear. Research carried out in The Netherlands has suggested that simply following a rigorous hygiene management procedure to control Johne’s disease will be just as, if not more, successful as administering the vaccine.
How To Prevent Johne’s Disease
Some prevention strategies for dairy herds are unsuitable for beef cattle and vice versa. However, here are some suggestions that should be effective on any cattle farm:
- Start to employ rigorous hygiene management practices, such as ensuring birthing environments are spotless
- Pay special attention to the udders of a nursing cow. If you do not have the time or workforce to keep udders or calving areas clean, you must consider separating the cow and calf
- Double-check for udder and teat cleanliness before obtaining colostrum
- If you administer colostrum to calves, ensure it comes from Johne’s negative cows
- Pooling or combining colostrum from several different animals is standard practice on some farms, especially in Ireland. Pooling is not advisable due to the high risk of spreading Johne’s. Again, comprehensive testing is essential
- Be careful to prevent manure contamination of foodstuffs and water. Store feed in lidded containers or raised storage bays. Ensure water supplies are well clear of any areas where manure is present
- Maintain scrupulous levels of hygiene when handling and disposing of any cattle feces
- Use artificial insemination or laboratory embryos to impregnate your cows