Gerald Hauer, DVM
Bison Production Specialist
Alberta Agriculture, Food and Rural Development
Bison Centre of Excellence, Leduc, Alberta.
Phone: (780) 986-4100
Reprinted from The Tracker, volume 4, issue 1, January, 2000, pages 6-8.
Johne’s disease is a bacterial infection of many farm animals that is receiving a lot attention lately because it has the potential to cause major economic losses in individual herds and because it has been implicated as a cause of Crohn’s disease in people. Bison are susceptible to the disease and it has been diagnosed in Alberta herds.
Johne's disease (pronounced yoe nees) is a bacterial infection that affects many ruminant species including elk and bison. Recently, there has been a lot of discussion about the disease in beef and dairy cattle because of the large economic loss that it can cause and because it has been suggested as a possible cause of Crohn’s disease in people. It is an issue that the elk and bison producers may also want to consider.Johne's disease is caused by a bacteria called Mycobacterium paratuberculosis which is closely related to the organism that causes tuberculosis (researchers are currently trying to determine if M. paratuberculosis may be responsible for some of the nonspecific skin reactions to the TB skin test in elk). Infection usually occurs in young calves, although older animals can become infected as well. In bison the disease is similar to cattle in that it slowly progresses until illness is seen when the animals are 2-5 years old, whereas in deer and elk it seems to develop more quickly and at a younger age. Infection occurs when the animal ingests bacteria in contaminated milk, feed, or water.
Once the infection has occurred, M. paratuberculosis resides in the lining of the small intestines where it causes inflammation and thickening. This inflammation eventually decreases absorption of nutrients and causes leakage of fluid out of the intestinal wall into the intestinal contents. As the disease progresses bouts of diarrhea occur while the animal's appetite remains normal. Within a few weeks or months the diarrhea becomes more frequent and weight loss is evident. In advanced cases the animal is very thin, has profuse diarrhea, eats poorly and dies from malnutrition because the intestines have lost their ability to absorb nutrients. By this time the bacteria has spread to other organs of the body.
Currently there is no effective treatment for this disease. Preventing infection of animals is the only way to combat Johnes but even this is difficult. Infected animals can shed the organism for a long time before showing clinical signs and it has been estimated that for every animal that is sick with the disease there are likely 15-25 other animals on the farm that are infected without showing any illness. Also, the organism can survive in the environment for up to a year making it difficult to keep premises clean. Culling animals that show clinical signs and preventing young animal's access to contaminated feed and water have been the methods employed in attempts to minimize the disease. The only way to effectively prevent Johnes is to establish a disease free herd by testing and culling infected animals. The tests currently available to detect infected animals are slow and not very accurate. New tests are being developed that show promise of being more accurate and quicker and have the potential to make herd testing easier.
To combat the disease cattle industries of North America are setting up programs that will certify herds that are free of the disease. The testing procedure involves a series of blood and fecal tests to identify and cull infected animals. This allows herds to be certified at different levels of confidence. The more times a herd is tested the higher the probability that there are no infected animals in the herd. The program is voluntary and it benefits the individual producers by eliminating losses caused by the disease and allows for the sale of Johnes free stock to other producers. Considering the importance of this disease, the bison and elk industries may want to consider a similar program.
For more information on Johnes disease visit the specialized livestock website of the Western College of Veterinary Medicine under ELK