Agriculture

Johne's Disease

Johne’s disease is a contagious chronic progressive bacterial infection of the digestive tracts of cattle, sheep, goats, deer, bison, llamas and alpacas. The occurrence of Johne’s disease is world wide. It was first reported in North America in 1908. The name Johne’s (pronounced yo-nees) comes from the German veterinarian, H.A. Johne who first discovered the disease in cattle in 1894.

The infection occurs in the layer of cells of the digestive tract that are responsible for absorption. This area becomes thickened as the body’s immune system attempts to control the infection.  The thickening prevents the digestive tract form absorbing nutrients which creates a chronic diarrhea that does not respond to treatment and subsequently leads to a loss of body condition in spite of a normal appetite.  There is no cure for Johne’s. Animals that develop clinical signs will eventually die from the disease. Clinical signs usually do not develop before 2 years of age.  However, the range is 6 months – 12 years with 5 years as the average. The long incubation period of this disease makes it a herd problem as well as an individual animal problem: Many animals can become infected before any in the herd show clinical signs. The primary way any herd becomes infected with Johne’s is through the purchase of infected animals.

What Causes Johne’s Disease?

Johne’s is caused by Mycobacterium avium subspecies paratuberculosis (MAP). It is a relative of tuberculosis and leprosy. It is an extremely hardy organism that will survive many environmental conditions, including freezing, especially if moisture or standing water is present. MAP is resistant to most disinfectants, including bleach. Formalin, creysilic and phenolic disinfectants are effective if contact times of 10 minutes or more occur. MAP is resistant to most antibiotics, including those used to treat tuberculosis in humans. It does not survive well in very alkaline soils (high pH), dry conditions or when exposed to sunlight (UV radiation). MAP is not free living, which means it does not replicate in the environment. It requires animal cells, specifically immune cells called macrophages, in order to replicate. It is very slow growing; culturing in the laboratory may take16 weeks.

What are the Clinical Signs of Johne’s?

The predominant clinical signs of Johne’s in cattle are a chronic severe watery diarrhea and a severe loss of body condition in spite of a good appetite. The onset of clinical signs occurs almost always in animals that are greater than 2 years old and often after a stressful event such as calving or transport. As the clinical signs progress, many animals will also develop fluid filled swellings under the jaw (bottle jaw). This is a result of the body’s inability to absorb protein.

Because of the slowly progressive nature of the disease, cattle can be infected for years before exhibiting clinical signs. Some infected animals may never exhibit clinical signs in their normal productive life times. While cattle exhibiting clinical signs shed the highest numbers of MAP, most infected animals will shed large numbers of MAP sporadically in their manure for months or years. The result is a “Tip of the Iceberg” phenomenon, where many animals in a herd can be infected with few or any showing clinical signs:  One infected cow showing clinical signs can indicate 1-2 more cows sick, but not yet obvious (clinical), 6-8 cows infected, but not yet sick (sub clinical) and 10 to 15 infected calves and young stock that may develop the disease later on in life.

How Does Johne’s Disease Enter a Herd and How Does it Spread?

The number one risk factor for MAP infecting a herd is through the purchase of infected stock. Once in a herd, MAP is primarily transmitted by ingestion of feed or water contaminated with manure from infected stock. MAP is also shed in the colostrum and milk of infected cows and the semen of infected bulls. All infected cows with clinical signs and between 9% and 36% of sub clinically infected cows shed MAP in their colostrum. 35% of infected cows with clinical signs and 3 – 19% of sub clinically infected cows shed MAP in their milk. MAP can also be passed on to calves while they are still in the uterus. This form of transmission is more likely to occur when the dam is in the later stages of clinical disease.

Calves are far more likely to become infected when exposed than older animals.  Young stock less than 6 months of age are the group at high risk for infection. Within this group, calves less than 1 month of age are at the highest risk. In young calves, the intestine is designed to be more “open” to allow the development of immunity to many pathogens. Unfortunately, it is believed this creates an easy route of infection for MAP. In order to prevent the spread of infection within a herd, it becomes critical to prevent exposure of calves to manure, colostrum and milk from infected cows. Although calves are at the highest risk of infection, it is important to remember that all age groups can be come infected if the exposure is high enough. Preventing the contamination of feed, water and bedding for the entire herd with MAP is critical in preventing the spread of Johne’s.

The Manitoba Picture

A survey in 2002 by Manitoba Agriculture Food and Rural Development (MAFRD) found that 68% of dairy farms and 29% of beef farms had 1 or more animals test positive on serum ELISA for Johne’s disease. 43% and 11% respectively had 2 or more test positive animals. Of the total number of animals tested, 4.5% of dairy cattle and 1.7% of beef cattle tested positive. The apparent prevalence in beef cattle / farms is comparable to other provinces and the U.S. The apparent prevalence in dairy cattle / farms is somewhat higher than normally found in other provinces or the U.S:  20% of farms tested had 2 or more positive animals in Ontario (2003), 17% in the Maritimes (1998) and 22% in the US (1996).

Why is the Prevention and Control of Johne’s Important?

Prevention and control for Johne’s disease is important to prevent significant losses from occurring. The most obvious losses that can occur in any herd are the loss of clinically affected animals that are culled before their normal productive lifetime is over.  Because of this increase in culling, more stock is required for replacements and, for herds that sell breeding stock, less are available for sale. Herds that are positive for Johne’s and sell breeding stock not only spread the disease but also sell animals that are likely less productive and have less longevity. 

Significant losses as a result of poor production occur in herds that have had clinical cases.  In US dairy herds that had greater than 10% of their culls showing clinical signs, there were 707 kgs (1559 lbs) less milk per cow per lactation.  In these same herds, the annual adjusted value of dairy production that is $227.00 less per cow than average. Overall, US herds that have a history of Johne’s disease have losses of $100.00 – $200.00 US per cow annually compared to those herds that do not.  A recent study involving Ontario herds found that test positive cows had 2% - 6% less milk production. This represents 173 kgs (381 lbs) – 548 kgs (1208 lbs) in a 305 day milk production. There was also an indication of less fat and protein production from test positive cows. This study indicated a 3 fold increase in culling rate for test positive cows. The overall loss per cow for each herd was $123.00 - $195.00 CAD. Sub clinical infections with Johne’s disease are also significant for beef production. Recent studies suggest that test positive cattle are slower to gain weight after calving and produce calves that have both lower birth weights and lower rates of gain while nursing the cow.

Of great concern are the potential losses associated with consumer confidence in meat and milk safety. The clinical signs of Johne’s disease have some similarities to Crohn’s disease in humans. Crohn’s disease is a type of inflammatory bowel disease, an incurable chronic inflammation of the intestinal tract that occurs in people 15 – 35 years of age. The major symptoms include weight loss and diarrhea. The cause or causes are still unknown. Any evidence linking the 2 diseases remains inconclusive at this point. What is known is that the incidence of Crohn’s and Johne’s is increasing. Some researchers have cultured MAP or have identified MAP DNA from a proportion of Crohn’s patients. Other researchers have been unable to duplicate these results. Studies in food safety have been done to determine if MAP could be cultured from pasteurized milk or meat.  Again the results are inconclusive, with some finding MAP and others not.  Currently, there is not a consensus within the medical community as to the significance of any association between the 2 diseases. Health officials do not recommend any changes in diet. The beef and dairy industries are based on the provision of healthy, wholesome products to consumers. Should a causal link be made between the 2 diseases, the resulting impact on consumer confidence is something producers should take very seriously.

How is Johne’s Disease Prevented or Controlled Within a Herd?

When implementing any disease control and/or prevention program, producers should first contact their herd veterinarians for advice. Veterinarians have the knowledge and expertise to assist producers in assessing the risks and determining what the most effective approach would be. The following are important points to consider with regards to Johne’s disease.

Test and cull programs that worked well for diseases such as Brucellosis are not effective for Johne’s disease. Testing for Johne’s disease, while important to estimate the level of infection on a herd level, is not accurate enough to test and cull individual animals: The prolonged incubation period means that infected animals under 2 years of age will not likely test positive. Infected adult animals will not always be at a stage in the disease to register a positive result. A combination of testing and the implementation of specific management practices are essential to prevent and control Johne’s disease.

Currently, fecal culture is the “gold standard” test. It is expensive, time consuming and can provide false negative results because an infected animal may not be shedding MAP when the sample for culture was taken. A positive fecal culture means the animal is definitely infected and shedding MAP in manure, but 55% of infected animals (who are likely not shedding) will culture negative.

ELISA tests that determine the level of antibodies (immune response) to MAP in either milk or blood are rapid, inexpensive and easy to do. They are almost as good as fecal culture at determining negative animals. However, they are only able to determine 28% to 61% of the culture positive animals. By extrapolation, these tests are only able to determine 10% - 30% of the actual infected animals in Johne’s positive herds.

Testing for Johne’s is still effective and necessary on a herd basis. By using the percentages listed above and testing only animals over 2 years of age with an ELISA test, an estimate of infection within the herd can be made. Any ELISA positive cattle if not culled, need to be considered suspect. Since Johne’s can be passed on through the placenta, colostrum and milk, relatives of positive cattle should also be considered suspect, even if they test negative. Fecal culture can be used for conformation, but as noted above, a negative result does not mean the animal is negative. 

The use of specific management practices are the most important way to control and prevent Johne’s disease. The best practices are those that prevent exposing young calves to infected manure, colostrum, or milk. The following can be considered critical control points for Johne’s prevention.

  • Limit the purchase of replacement and breeding stock as much as possible. When purchasing stock, it is best to buy younger animals from herds that have implemented a Johne’s control program. If purchasing older animals, testing should be considered in spite of the limitations.
  • Cull infected animals: Cattle that exhibit clinical signs or are fecal culture positive should be removed from the herd as soon as possible.
  • Provide special handling of suspect cattle – those that test positive to an ELISA test or are relatives of clinically affected cows. 
    • Suspect cattle, if they are to stay in the herd, should not be housed in group calving pens, hospital pens or with young stock. This would include pastures.
    • Calves from these animals should receive colostrum from a negative source and be removed from the dam immediately.
    • Make sure these animals are marked in a way that makes them easily identifiable. Notched ear tags or different colored tags are methods that can be use.
  • Keep calving areas clean and dry: Reducing the exposure of new born calves to manure is critical in preventing the disease. 
    • Calving areas can be quickly assessed by kneeling down on the bedding pack. The pack should be dry and bedded enough to prevent the knees from getting wet. Regular cleaning of maternity pens with the use of lime will help. 
    • For beef herds it is best to provide calving areas separate from wintering areas.
    • For dairy herds, it is best to provide a separate calving area from the dry cow group.
    • It is important to not use maternity pens as hospital pens.
  • Keep calves segregated: While unrealistic for beef herds, this is an essential practice for dairy herds.
    • Calves should be raised separately from mature animals until they are ready to calve. Take care to prevent manure run off and splatter from adult cattle contaminating the feed, water, and bedding areas of young stock.
    • 'If possible, calves should be removed from their dams immediately after birth. If removal is not possible, then procedures that prevent exposure to manure in the calving pen and on the udder should be implemented.
    • Colostrum from negative and / or younger cows is preferred; younger cows are less likely to be shedding MAP. Alternatively a dried commercial colostrum product or pasteurized colostrum can be used.
    • Feeding raw milk or waste milk is not recommended. High quality milk replacer is preferred. Otherwise feed only pasteurized milk or milk from negative cows.
  • Prevent manure contamination of feed and water: 
    • As much as possible, use separate equipment for feeding and manure handling. Otherwise, implement procedures that allow for cleaning of equipment between the different uses.
    • Care should be taken to not travel through feeding areas with tires, boots or equipment covered with manure.
    • Prevent animals from walking through feed or water areas. Fence line feeding, raised feed bunks and feed barriers that allow only the head and neck of the animal access should be utilized. Dug outs, swamps and natural ponds should be fenced off to prevent manure contamination of the water supply.
    • Separate waterers and feed bunks are preferred for young stock. Prevent manure build up around waterers and feed bunks.
    • Do not allow grazing in the same season as manure application. Keep stocking rates on pasture as low as possible.
  • Keep facilities clean and handle manure properly:
    • Clean corrals, cattle sheds, barns and holding pens frequently. Ensure that drainage from these areas do not contaminate feed or water.
    • Store manure in areas where cattle do not have access. Proper composting is believed to reduce MAP in manure. However, this has not been fully investigated.
    • It is preferable to spread manure on crop land. If manure is applied to hay or pasture land, do not use in the same season.

Implementing a prevention and control program for Johne’s disease requires a long term commitment. It is important to maintain and review the plan once it is in place. If your herd is considered to be low probability of having Johne’s, it is still important to implement the control points listed above. This will help minimize spread if the disease is introduced and will help control for other diseases, such as calf scours.


Additional Information 


Contact

 
For more information, please contact the Chief Veterinary Office (CVO).