Johne’s disease is a fatal gastrointestinal disease of goats and other ruminants (including cattle, sheep, elk, deer, and bison) that is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). Also known as paratuberculosis, this infection is contagious, which means it can spread in your herd. The MAP organism is most commonly passed in the manure of infected animals. The infection usually spreads from adult goats to kids and occurs when a young animal swallows the organism via water, milk or feed that has been contaminated by manure from infected animals.
The costs of this infection range from economic losses—due to reduced production and increased culling for meat and milk animals—to emotional losses—for those whose goats are pets.
There is no cure for Johne’s disease, and there is not an approved vaccine for goats to help protect them from infection. Therefore, prevention is the key to control. A goat that appears perfectly healthy can be infected with MAP and although goats may become infected in the first few months of life, many remain free of clinical illness until months or years later. When goats finally do become ill, the symptoms are vague and similar to other ailments: rapid weight loss and, in some cases, diarrhea. Despite continuing to eat well, infected goats soon become emaciated and weak. When an animal with signs of Johne’s disease is discovered, it is very likely that other infected animals—even those that still appear healthy— are in the herd. Control of the infection requires that you and your veterinarian address it in the whole herd and not just on an individual animal basis.
In an animal that is infected with MAP, the bacteria reside in the last part of the small intestine—the ileum—and the intestinal lymph nodes. At some point, the infection progresses as bacteria multiply and take over more and more of the tissue. The goat’s immune system responds to the bacteria with inflammation that thickens the intestinal wall and prevents it from absorbing nutrients. As a result, a goat in the clinically ill stage of Johne’s disease in effect starves to death. At this stage the organism may also spread beyond the gastrointestinal tract, travelling in the blood to muscles or other major organs such as the liver or lungs.
Johne’s disease usually enters a herd when an infected, but healthy looking, goat is purchased. With MAP hiding in its small intestine, this infected goat sheds the organism in its pellets and into the environment—perhaps onto pasture or into water shared by its new herdmates. Goats are at risk when they repeatedly swallow the organism, especially when they are young (less than 6 months old). If the doe is infected, her offspring can become infected even before they are born (in utero transmission). The organism is also shed in an infected doe’s milk and colostrum. Kids are most susceptible to infection with MAP and often become infected through ingestion of manure containing MAP—such as from suckling manurestained teats, swallowing milk that carries MAP or eating feed, grass or water containingMAP-contaminated manure. Bottle-fed kids can also become infected if the milk was contaminated. Heat treatment used to control CAE in milk is not suffi cient to kill MAP organisms.
Since goats usually produce more than one kid per birthing, Johne’s disease can spread swiftly through a herd, especially if the infection remains undetected for several kidding seasons. While there seems to be age-related resistance to Johne’s disease, some older goats may become infected, particularly when their immune systems are suppressed for other reasons. Johne’s disease can be transmitted from one ruminant species to another—for example from cows to goats, goats to sheep, etc. Infected goats shed MAP in their manure on and off throughout their lives. The older the animal, the more likely that shedding occurs as the infection progresses. As goats enter the latter stages of infection and clinical signs begin to appear, the infective organism is shed more often and more heavily.
Test Method: ELISA for detection of antibodies in serum or milk, acid-fast bacilli test in fecal samples
Testing time: Same day