Johne's Disease in Beef Cattle

Johne's disease, pronounced YO-knees, was identified more than a century ago, yet remains a common and, sometimes, costly infectious disease of beef and dairy cattle. The infection is caused by a bactera Mycobacterium avium ss. paratuberculosius.  Furthermore, Johne's disease is not limited to cattle, since it has been diagnosed in a variety of domestic and free-ranging animals, such as sheep, goats, deer, llamas, elk, and bison, and other ruminants. Johne's disease has been reported in almost all countries around the world.

A recent study in the US indicated US beef producers are unfamiliar with Johne's disease; in fact 92.2 percent of beef producers were either unaware of Johne's disease or recognized the name but knew little else about it. Lack of familiarity with Johne's disease was generally present across regions of the country and across sizes of operations

This lack of familiarity has hindered control and prevention of Johne's disease in this country, and efforts are currently underway to educate beef producers about Johne's disease.

Johne's disease typically starts as an infection in calves, though clinical signs do not generally appear until cattle are 2 to 5 years of age. The infection is difficult to detect in its early stages. In dairy cattle it reduces milk production and the productive life of cattle. Though not well documented, similar effects are thought to occur in beef cattle. There is no cure for Johne's disease once an animal becomes infected.

Producers and others in the industry need to be familiar with Johne's disease and its implications for their operations. While this is a complex disease that we do not completely understand, basic information is available about the bacteria that cause Johne's disease, how it is transmitted, and how to control it.

Johne's Disease Prevalence

A US study conducted over a decade ago sampled cattle at slaughterhouses and, finding a low prevalence of infected cull cows, failed to generate concern about Johne's disease. In that study, 2.9 percent of culled dairy cows and 0.8 percent of culled beef cows showed evidence of infection with the Johne's organism. A recent slaughter house study in Alberta indicates the prevalence is significantly higher.

The USDA Beef '97 study, blood samples from 10,372 cows in 380 herds from 21 states were submitted for testing. Of these samples, 40 (0.4 percent) were positive for antibodies to the organism that causes Johne's disease. These 40 positive animals were from 30 (7.9 percent) of the tested herds.

Though these percentages are low, readers should keep in mind that the sampling protocol was designed to identify herds with at least 10 percent of the animals infected. It is possible that the within-herd prevalence could have been lower than 10 percent in beef herds that were more extensively managed, and the study likely failed to identify most of these herds. The estimated prevalence of 7.9 percent should be considered a conservative estimate.

In addition, this study was set up to evaluate prevalence across the industry in general. Prevalences in certain locations of the country or in certain types of operations may be higher than the industry level as a whole. However, this study could not detect these differences. Since purebred operations supply genetics to a wide cross-section of the industry, future studies may attempt to evaluate this segment of the population more closely. As for now, given the low level of sampling in purebred operations in this study, there is not enough information to say whether this group is at lower or higher risk of being positive for Johne's disease.

Manitoba Cattle Producer Association is sponsored a survey in 2001-2002 to identify the prevalence of Johne’s Disease in Manitoba Beef Herds. In 49 randomly selected beef herds, 1425 individual cows were tested returning only 15 positive results to the serum test for an apparent prevalence rate of 1.05 percent .

About the Disease

Johne's disease results from infection with bacteria called Mycobacterium paratuberculosis. This organism grows very slowly, causes a gradually worsening disease condition, and is highly resistant to the infected animal's immune defenses. Therefore, infected animals may harbor the organism for years before they test positive or develop disease signs.

The bacteria primarily infect the intestine, leading to prolonged diarrhea, poor digestion, and excessive weight loss. Diseased animals do not refuse feed until they are severely affected. These bacteria are typically shed, in varying numbers, in an infected animal's feces. Once outside the animal, the bacteria no longer multiply, however they are quite hardy, living for months in water, feed, and manure. Susceptible, non-infected animals may then pick up the bacteria through fecally contaminated feed or water. These newly exposed animals may develop disease and spread it within the herd.

Calves less than 6 months old are most vulnerable to infection. Under intensive housing conditions with a high level of exposure of young cattle to the organism, clinical Johne's disease can become common in cattle from 1 to 3 years of age. As Johne's disease begins to spread in a herd, one or two animals may show clinical disease signs at a time. These sick animals are culled, and the disease may go unrecognized as a whole herd problem for some time.

Recent research has added to our understanding of Johne's disease transmission. Contrary to earlier notions that fecal contamination of feed and water was the sole means of transmission, infection of calves before they are born is possible. Fetal infection can occur in 20 to 40 percent of calves from infected cows showing clinical signs and about 10 percent of calves from infected cows not showing clinical signs. The bacteria may also be shed directly in milk and colostrum from infected cows, even without fecal contamination.

About Testing

Both fecal culture and blood serum antibody tests are available to producers to determine the disease status of a herd or an animal. Current tests are good tools, although they have some limitations, particularly in accurately determining the status of the individual animal. Both tests fail to detect early infections because blood antibody development and detectable fecal shedding do not usually occur until late in the course of the infection. In addition, blood serum antibody tests can give false positive results which is why actions with regard to an individual animal with positive test results should be made in consultation with a veterinarian. It may be helpful to confirm results with another type of test.

The difficulty in detecting early infections and the long period before clinical signs develop may allow Johne's disease to remain a hidden herd problem. However, informed use of tests along with a history of clinical signs of disease in the herd can provide information to assist disease management in the individual cow and the herd.

Liability

Producers should consider ethical responsibilities and the potential for legal liability. Absence of a definitive diagnosis of Johne's disease may not protect producers from legal liability for selling infected animals.

Public Health

Johne's disease bacteria, M. paratuberculosis, has been isolated from a few humans with Crohn's disease, as have numerous other bacteria and viruses. Since results from various studies evaluating the role of M. paratuberculosis in Crohn's disease have been contradictory, uncertainty about potential risk to public health from this organism persists. Some researchers have concerns about M. paratuberculosis bacteria in undercooked meat, unpasteurized milk products, and water.

Because of continued potential public health concerns relating to this disease, animal production industries must give this disease more attention.

Control

Principles of Johne's disease control include:

• reducing exposure and infection of replacement cattle on farm
• identifying and removing the most highly infected cattle, and
• preventing introduction of infection by screening sources of off-farm replacements

Johne's disease control programs require a long-term commitment to prevention and must be adapted to individual herds. This approach, however, has not yet been widely adopted by veterinarians and producers.

Opportunity for the Beef Industry

The estimated low prevalence of Johne's disease in beef herds could offer a bigger opportunity for the industry. A buyer beware strategy combined with herd status programs to identify and protect non-infected herds in the US could feasibly eliminate Johne's disease as a future problem for the beef industry. An example of such a program is the Voluntary Johne's Disease Herd Status Program (VJDHSP) for cattle, approved by the US Animal Health Association in 1998.

Taking an example from Australia, industry and government implemented the Australian Johne's disease cattle Market Assurance Program in 1996. This program is similar to the US VJDHSP for cattle. The Australian program encourages low-risk herds to test to identify their status for buyers and publicizes the message for buyers to ask sources for a declaration about Johne's disease status. The industry has recognized the opportunity and advantage of protecting herds in uninfected regions of the country and eliminating Johne's disease from herds in the low prevalence areas, before the infection spreads further. The Australian sheep and llama industries have followed with similar programs.

Finding Replacements

Since Johne's disease occurs throughout the US, identification of uninfected or low-risk herds as sources of replacement heifers and bulls would be beneficial. Currently, identification of infected animals before they are in an advanced disease stage and/or shedding significant numbers of pathogens in their feces is not very accurate. This limitation makes it difficult to prevent the introduction of disease when adding new cattle to beef operations. Questions about choosing a source for replacement heifers and bulls and the appropriate disposition of young stock from a positive herd remain difficult to answer.

The VJDHSP for cattle uses repeated herd testing to provide the best assurance of obtaining low-risk cattle for replacements. This practice represents a lower risk than introducing untested or test-negative cattle from a herd with no documentation as to its actual Johne's disease status.

Awareness About the Disease

Several US states have Johne's disease advisory boards and control programs in place, or are in the process of implementing them. State efforts should help to increase education about Johne's disease and develop constructive state policies to support the industries in controlling it and identify source herds at low risk. Good information and veterinary and industry involvement are needed to appropriately address the impact of Johne's disease in the industry.

The US Beef '97 study highlighted the need for education by showing that 92.2 percent of beef producers were either unaware of Johne's disease or recognized the name, but knew little else about it. Lack of familiarity has limited adoption of Johne's disease prevention efforts. Interested beef producers are encouraged to find out more about efforts in their state and perhaps consider participating on a board.

What's Next?

The time is past when we could think of the major impact of Johne's disease as an occasional cow with diarrhea that could be culled and forgotten. Johne's disease is a herd problem that worsens with time, reducing production and profit. It may even come under further scrutiny as a risk to human health. Implications of Johne's disease should be considered by all beef producers, and control strategies are available for implementation.

On a more direct level, we believe all beef producers should ask themselves the following questions:

• Is Johne's disease important to me?
• How can I identify Johne's disease in my herd?
• If I find it, what should I do?
• If my herd doesn't have Johne's disease, how do I keep it out?

For more information on Johne’s Disease and control programs contact your local Practitioner.