Crohn’s Disease

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Achieving Remission of Crohn’s Disease


A new disease eradication scheme will be launched this week as the dairy industry looks to protect the €1.7bn of annual infant milk formula sales from a ‘BSE-style’ disaster.

There is a growing body of data linking Johne’s with the debilitating Crohn’s disease in humans, while the spread of Johne’s in national cattle herds continues at an alarming rate.

Veterinary experts believe that up to 20pc of Irish herds – in both beef and dairy – are carrying the disease. Globally, it may be closer to 50pc in intensive dairy regions.

Although details surrounding the voluntary programme have been kept under wraps for months, the Farming Independent has learned that cost analysis by Teagasc’s economics unit has estimated the total bill for the first seven-year period of the programme to be north of €85m.

The lion’s share of the costings will be associated with the blood testing required from every animal over two years. It is envisaged that this could be rolled into the annual TB test, although the cessation of the brucellosis annual blood testing regime has increased the basic costs involved.

Overall, the costs per animal are estimated to be €5-6, but experts remained tight-lipped on the details ahead of Thursday’s launch by Animal Health Ireland.

The body will be aware of the pitfalls of making this latest disease eradication drive a success given the difficulties encountered by the BVD eradication programme. It was hoped that a successful BVD programme would pave the way for farmer buy-in for the much more difficult task of eliminating Johne’s, which experts believe could take over a generation to achieve.

Michael Collins is a professor of pathological sciences at the University of Winsconsin. He believes that the evidence linking the disease to the similar human wasting condition, Crohn’s, will only continue to mount.

Johne’s Disease

Animal Health Australia (AHA) coordinates industry-funded projects to manage Johne’s disease (JD) in sheep, cattle, goats and alpaca.

Our projects work to protect Australia’s favourable JD status and reduce the impacts of the disease and its control measures on the livestock industries.

What is Johne’s Disease?

JD is a serious wasting disease that affects various species of animals. In Australia, JD has been found in cattle, sheep, goats, deer and camelids.

JD infections are caused by the bacterium, Mycobacterium paratuberculosis, which live mainly in animal intestines, but can survive in the outside environment for several months.

JD bacteria affect animals by causing a thickening of the intestinal wall resulting in a reduction in the normal absorption of food. The infected animal is hungry and eats, but cannot absorb any nutrients. This results in wasting and finally death. Diarrhoea and bottle jaw are also common signs in cattle.

A number of strains of M. paratuberculosis have been identified and it is recognised that they are all capable of infecting a number of ruminant species.

Johne’s disease in Australia

Australia is in the fortunate position of having relatively little Johne’s disease compared to most developed agricultural countries.

Large areas of Australia are Johne’s disease-free, and a high proportion of Australia’s livestock populations have no known infection.

Australians are actively involved in international organisations and research dealing with Johne’s disease (see International Colloquium on Paratuberculosis).

AHA manages the National Johne’s Disease Project (NJDP), a cooperative initiative of the Australian livestock industries, governments and veterinarians.

Johne’s disease in cattle

Cause of JD

JD is caused by M. paratuberculosis, which lives mainly in the intestines of infected animals. It causes the intestinal wall to thicken and reduces the normal absorption of nutrients from grazing. An infected animal can eventually starve to death.

Johne’s disease may be transmitted between cattle and sheep, where co-grazing occurs and one of the two species becomes infected.

The bacteria causing JD are resilient and can live for a long time in the environment. Research in southern Australia showed that heat and sunlight destroyed the bacteria; under normal summer conditions in paddocks and waterways, around 90% of the bacteria die within 6 weeks. But in moist, shaded conditions, JD bacteria can survive for longer than 12 months.

Cattle infected with JD excrete the bacteria in their manure. The bacteria contaminate pasture and watercourses, spreading infection to other cattle sharing the same paddocks or yards.

Eradicating JD from an endemically infected herd is difficult.

Clinical signs and symptoms of JD

Most cattle are infected as calves but often do not show any symptoms of JD for many years. They are likely to excrete the JD bacteria before developing clinical signs.

The numbers of infected cattle in a herd may start out low, but the rate of infection can increase significantly if JD is not controlled. In addition to the risk of spreading the disease, visibly sick and dying animals can cause animal welfare issues and reduce enterprise production.

The most common signs of JD in cattle are:

  • chronic diarrhoea (scouring)
  • wasting
  • eventual death.

Not all infected cattle show these signs; some just fail to reach their full productive potential.

First signs of JD in dairy cattle are:

  • a drop in milk production
  • then weight loss and—in most cases—scouring.

This would occur even though you are feeding the cattle well. Bottle jaw (soft fluid swelling under the lower jaw) can also be seen in the early stages.

First likely sign of JD in beef cattle is weight loss, with or without concurrent scouring.

Johne’s disease in sheep – ovine Johne’s disease

Cause of ovine Johne’s disease (OJD)

OJD is an incurable, infectious wasting disease of sheep that can result in significant economic losses on infected farms due to sheep deaths and lost production of sheepmeat, lambs and wool, when not managed.

OJD is caused by the sheep strain of the bacterium M. paratuberculosis, which leads to the intestinal wall slowly thickening, causing reduced absorption of nutrients from the intestine. This eventually leads to severe loss of condition. An infected sheep can waste away and die.

Sheep infected with OJD excrete the bacteria in their manure, contaminating pasture and water supplies and spreading infection to other susceptible sheep.

Eradicating OJD from an endemically infected flock is difficult.

Clinical signs and symptoms of OJD

OJD is often not diagnosed in a flock until a significant proportion of the flock is already infected and deaths are occurring.

There is often no sign for the first few years, which is why OJD may be referred to as a ‘silent but costly disease’.

Infected sheep can be shedding the bacteria in their manure for a considerable period (sometimes years) even though the flock still looks healthy, but they are contaminating the pasture and infecting other sheep.

The first sign of the disease in a mob is usually a distinct ‘tail’, with sheep ranging in condition from good to very poor, then the sheep in the ‘tail’ start dying.

The number of sheep in this classic ‘tail’ may be constant, but it’s comprised of different animals over time, eroding flock numbers and profits.

OJD-infected sheep continue to eat and drink normally until they are too weak to graze, and eventually die.

Scouring may occur, but is not a common feature of Johne’s disease in sheep.

In some large flocks, the number of deaths may only be appreciated when big discrepancies occur in counts of adult sheep.

When obvious OJD deaths are noticed, the disease is likely to be well established. It will take the producer some years to get the situation under control, during which time deaths will continue.

The best place to look for the disease is in 2 and 3-year olds, but sheep from weaners through to older adults can also die from the disease.


Johne’s Disease at a Crossroad Frank Garry, DVM, Coordinator of ILM, Colorado State University and Mike Collins, DVM, PhD, University Of Wisconsin – Madison Why is there so much fuss about Johne’s disease in dairy cows? In the last six years the State of Colorado, as well as most of the other states in this country have developed voluntary bovine Johne’s disease control programs modeled after the national program standards. Several commercial companies have developed and marketed tests for rapid identification of infected animals. In 2003 the federal government allocated more than $20 million to support efforts to control this disease. About 22% of U.S. dairies have JD infection in 10% or more of their cattle, according to the 1996 NAHMS Dairy survey, The NAHMS study also estimated about a $220 annual loss of production per cow in the herd when infection rates were that high. Cattle with JD lose weight and develop diarrhea. Their production declines and affected cows will ultimately die from the disease, but they are usually culled prior to death. Decreasing the economic losses associated with JD can improve a dairy’s bottom line, but there are many other health problems such as infertility, lameness, mastitis, and calf death that can cost producers as much or more in losses. So why has Johne’s disease caught so much attention that it warrants federal spending to assist in its control? The answer, of course, is that there is ongoing concern that the infectious agent that causes JD in cows (Mycobacterium avium paratuberculosis, MAP) may also be part of the cause of a human disease called Crohn’s disease. Infections that occur in both humans and animals are called zoonoses. The possibility that JD is a zoonotic disease like TB or brucellosis is a major concern. Whether Crohn’s disease is caused by infection with MAP is an extremely important question that needs to be determined by the human medical community. However, that determination will also have profound effects on the approach to dealing with Johne’s disease in livestock. As depicted in the figure below, if Johne’s disease is considered to be an animal disease without public health impacts, then control programs will logically follow the course currently being undertaken. Specifically, such control programs are based on the economic importance of the disease to producers, and include voluntary program participation with limited public subsidies. The target of such control efforts would be keeping JD occurrence low enough to minimize its impact on productivity. On the other hand, if the disease is believed to be zoonotic, then aggressive control programs with mandatory testing and substantial public subsidies would be highly likely. Designation as a zoonotic disease would put this animal health problem in the same league as TB, brucellosis, West Nile disease, rabies, or anthrax. There is a good deal of scientific evidence supporting the possibility that MAP is indeed a zoonotic infectious agent. Whether this evidence is sufficient to conclusively say that MAP is part of the cause of Crohn’s disease is the pertinent question. Some of the key evidence is listed below: 1. The majority of studies that used appropriate techniques have detected MAP genes and even grown MAP bacteria from patient tissues. 2. A statistically significant number of Crohn’s patients test positive for serum antibody to MAP. 3. MAP has been shown to be capable of infecting a wide range of animals including primates. 4. MAP is guilty by association: all mycobacterial pathogens are zoonotic (examples include the causes of TB in humans, TB in cattle, TB in birds, and leprosy). 5. Antibiotic treatments directed against MAP can cure Crohn’s disease in a high proportion of patients. however, these studies are limited in number. The National Academy of Sciences recently convened a committee to review information on Johne’s disease, and included an assessment of the link between JD and Crohn’s disease. The report can be read online at the National Academy Press website, by doing a title search on Johne’s disease. The committee asked the question “What data would it take to convince us that such a link exists?” The committee concluded that Crohn’s disease is a complex problem without a simple cause, and that there was insufficient evidence to prove or disprove that MAP is a cause of Crohn’s disease in humans. However, a causal link between MAP and Crohn’s is a plausible hypothesis that warrants further research. There are indeed a growing number of research reports that point to an infectious agent as one of the contributors to Crohn’s disease. Additionally, the most common infectious agent toward which these studies point is MAP. There are also numerous studies that fail to identify a causal role for MAP. Such conflicting results are expected if a disease problem has a complex, multifactorial cause. Therefore, it is unlikely that there will be flawless scientific proof of cause and effect, and a determination will rely on the collective judgment of medical investigators. Until a convincing argument is made one way or the other, the issue will remain controversial. However, if sufficient public concern develops, then the safety of dairy products, cull cow meat, and water supplies potentially contaminated with animal feces will become important issues. Two recent articles by Patrick Perry in the Saturday Evening Post (March/April and May/June, 2004) are good examples of the type of lay press publications that can lead consumers to draw conclusions about the cause of Crohn’s that specifically suggest dangers associated with dairy products. This concern may have negative repercussions regardless of the judgement pronounced by medical experts. Although there is no firm consensus yet about the relationship between MAP and Crohn’s, there is no question that this debate is gathering substantial attention. Clearly this is an important question for the dairy industry and many public policy decisions hang in the balance. If MAP is ultimately considered to be a human disease agent, then the occurrence of JD in cows will surely be considered an important risk to human health. The dairy industry is at a crossroad on this issue. Producers and veterinarians can choose to act now to minimize the occurrence of this infection, and the developing state programs can help focus these efforts. Alternatively, we can wait until someone defines an answer, and then see if public pressure or government regulations mandate the effort. For more information on Johne’s Disease in general and the Colorado Voluntary Control Program, please visit the archives of the Colorado Dairy News posted on the web at <>. Figure One: The approach to control of Bovine Johne’s Disease will vary depending on whether or not it is considered a zoonotic disease.