Johne's Disease in Goats

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Johne’s (“YO-knees”) 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. Most owners are taken by surprise when the infection is diagnosed, and learn too late that the infection has taken hold in multiple animals in a herd.

Due to lack of testing and reporting, it is not known how widespread Johne’s disease is in goats in the United States. The infection has been confirmed, however, in many goat herds throughout the country—in milk, meat, heritage and other breeds—and it is a problem in most other goat-rearing countries as well. 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 more pets than agricultural investments.

There is no cure for Johne’s disease, and there is not anapproved vaccine for goats in the United States to help protect them rom infection. Therefore, prevention is the key to control.

A goat that appears perfectly healthy can be infected with MAP. Although goats 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 goat soon become emaciated and weak.

Since the signs of Johne’s disease are similar to those for several other diseases— parasitism, dental disease, Caseous

Q: Lymphadenitis (CLA) and Caprine Arthritis-Encephalitis Virus Why do goats with clinical signs of Johne’s disease (CAEV)—laboratory tests are needed to confirm a diagnosis.lose weight and become weak? A: When an animal with signs of Johne’s disease is discovered, it is very likely that other infected animals—even those When an animal is infected with MAP, the bacteria reside in that still appear healthy— are in the herd. Control of the the last part of the small intestine—the ileum—and the intestinal lymph nodes. At some point, the infection progresses as bacteria multiply and infection requires that you and your veterinarian address it in take over more and more of the tissue. The goat’s immune system the whole herd and not just on an individualresponds to the bacteria with inflammation that thickens the intestinal animal basis. wall and prevents it from absorbing nutrients. As a result, a goat in the When an animal is infected with MAP, the bacteria reside clinically ill stage of Johne’s disease in effect starves to death. At this in the last part of the small intestine—the ileum—and the stage the organism may also spread beyond the gastrointestinal tract, intestinal lymph nodes. At some point, the infection protravelling in the blood to muscles or other major organs such as the liver or lungs. gresses 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

Top: Thickened intestinal mucosa caused by Johne’s disease. gastrointestinal tract, travelling in the blood Bottom: Thin, pliable, normal intestine to muscles or other major organs such as the liver or lungs. Since there is no cure for Johne’s disease, control of the infection is critical. Control of Johne’s disease takes time and a strong commitment to management practices focused on keeping young animals away from contaminated manure, milk, feed and water. A typical herd clean-up program may take a number of years. The basics of control are simple: new infections must be prevented, and animals with the infection must be identified and removed from the herd. Your State Designated Johne’s Coordinator can help you undertake an on-farm risk assessment that evaluates your operation, your resources and your goals. The University of Wisconsin School of Veterinary Medicine’s Johne’s disease website—www.johnes.org—addresses all aspects of Johne’s disease for multiple species,

including goats. The site has an “Ask An Expert” feature that allows you to submit your own questions and receive a personalized response from an expert. The University of Wisconsin School of Veterinary Medicine also offers a free online course for goat producers. Simply go to www.vetmedce.org, click on “Courses” in the lower left hand corner of the homepage. Once on a new page, click on “Johne’s Disease.” At the next new page, click on “Johne’s Disease Courses for Producers” followed by clicking on “0017—Johne’s Disease for Goat Producers.” To learn more about Johne’s disease in goats, please contact your State animal health regulatory agency or your State Designated Johne’s Coordinator. Contact information for your State’s Johne’s diseas program is available online at www.johnesdisease.org when you click on “State Contacts.”

Additional information and resources available at http://www.johnes.org/. Information reprinted with permission by Michael T. Collins, DVM, PhD, DACVM, Johne’s Testing and Information Center, School of Veterinary Medicine, University of Wisconsin-Madison.

How Do You Control Johne's Disease in a Goat Heard?

The best methods for MAP infection control in your goat herd depend on the resources available, the goals of your enterprise, and the methods you use to take care of your goats. All control methods however rely on two core strategies that must be employed at the same time: Kids must be protected from infection by being born and raised in a clean environment and fed milk and water free of MAP contamination. The primary sources of MAP contamination are manure and/or milk from infected adult animals. Adult animals infected with MAP must be identified and culled managed to ensure no kids are exposed to their milk or manure. Because twins are common for goats, the annual risk of a new case born to an infected doe is believed to be twice the risk seen in species that produce just one offspring a year. No vaccines are available in the United States for Johne’s disease in goats, however, in Spain, Australia and several other countries vaccines are used.

What are the symptoms of Johne's Disease and what causes them?

There really are only two clinical signs of Johne’s disease: rapid weight loss and diarrhea. In goats, diarrhea is less common than in cattle. The MAP infection occurs in kids in the first months of life, but signs of disease usually do not appear until the animals are adults. Despite continuing to eat well, adult goats become emaciated and weak. Since the signs of Johne’s disease are similar to those for several other diseases, laboratory tests are needed to confirm a diagnosis. If a case of Johne’s disease occurs, it is very likely that other MAP-infected goats, that may still appear healthy but are incubating the infection, are in the herd. No one yet understands what causes a clinically normal goat that has been infected by MAP for months or years to suddenly become sick from the infection.We do know that at some point the MAP that have been lying quietly within cells of the last section of the small intestine (called the ileum) start to replicate and take over more and more of the tissue. The animal’s immune system responds to all these organisms with what is called granulomatous inflammation. This inflammation thickens the intestinal wall, preventing it from functioning normally. This, among other factors, means the animal cannot absorb the nutrition it needs and thus begins to lose body condition, milk production drops off, and diarrhea may occur. In effect, an animal with Johne’s disease is starving in spite of having a good appetite and eating well.

How do Goats Get Infected?

Johne’s disease typically enters a herd when a MAP-infected, but healthy-looking, goat is purchased. This infected goat then sheds MAP in its feces onto the premises – perhaps onto pasture or into water shared by its new herdmates. Young animals are far more susceptible to infection than are adults: these kids swallow the organism along with grass or water. Perhaps they are bottle-fed with MAP-contaminated milk collected from the infected but healthy-appearing new arrival. Milk may become contaminated from the environment (manure-stained teats) or, in the advanced stages of the infection, the bacterium is shed directly into the milk. Animals may even have been infected before they are born, called in utero transmission, if the doe is in advanced stages of the MAP infection. Thus the infection spreads insidiously,