JOHNE'S DISEASE

The existence of Johne's Disease is unknown to many goat breeders in the meat-goat industry. The reason for this lack of knowledge is primarily due to the elusive nature of the disease.

Johne's (pronounced Yo-nees) is a contagious disease which can infect any ruminant species. The origin of the disease is unknown, it is world-wide, and it was first diagnosed in goats in the early 1900's. Johne's is a chronic infection that localizes in the small intestine, causing a thickening of the intestinal wall which prevents the normal absorption of nutrients. In goats, the symptoms do not appear until the last stages of the illness.

Mycobacterium paratuberclosis is the organism which causes Johne's Disease, and this bacteria is passed in the manure of goats from animal to animal via fecal-to-oral contact. Young kids are the most susceptible, and the disease remains unidentifiable for years after the kids have first ingested infected feces. Clinical weight loss in infected adults is the only symptom.

The symptoms are prolonged weight loss, lack of appetite, and depression, occasionally followed by diarrhea. Goats infected with Johne's frequently are more subject to heavy parasite loads. Any adult goat which is continually parasite-infected should be tested for Johne's Disease.

Clinical signs of this disease do not appear until goats are yearlings and sometimes much later. Kids can contract Johne's in utero (before birth) if their dams are heavily infected. Kids can also become infected through the colustrum and milk of Johne's-carrying mothers. Neither heat-treating colustrum or pasteurizing milk kills this bacteria; it is quite heat resistant, and like Caseous Lymphadinitis (CL), the organism can live for years in the soil and surrounding environment.

The appearance of the disease is affected by the dosage (concentration and amount) of bacteria ingested, the age of the kid, and the genetic make-up of the animal. If a kid receives a high dose at an early age, the kid will most likely begin shedding the disease in its feces and showing clinical signs of infection at an earlier age than a kid who received a low dose of the bacteria. Some goats are carriers and never show clinical signs of the illness. There seems to be an age-related resistance to Johne's Disease, but older goats can become infected, particularly in overcrowded and unsanitary conditions.

Generally speaking, overt signs of infection begin to show after many years of shedding the bacteria, particularly if the animals are managed well, with good nutrition, clean conditions, no overcrowding, and minimal stress in their lives. Once it is evident that infection is present, the Johne's-infected goats usually live less than one year and ultimately die from their inability to absorb nutrients from their intestinal tracts.

The timeline runs from birth to age one, no signs whatsoever; from age two to four, goats may begin to show signs of some weight loss but have no decrease in appetite until the disease becomes full-blown; and goats over age four who are heavily-loaded with the bacteria begin to look wasted. The mid-stage, from age two to four, is the really dangerous time, because those goats look reasonably well but are shedding the bacteria like crazy. Johne's is rarely seen in goats over seven years old.

There are three commonly available tests for diagnosing Johne's Disease. Culturing fecal matter to detect the organism is the most accurate, but the bacteria grows slowly and the test takes six weeks to four months to complete. If the animal being tested is not shedding the organism in its feces, it can test negative even though it may really be infected. Repeat testing on suspect goats is essential.

The AGID (Agar-Gel Immune Diffusion) and the ELISA (Enzyme-Linked Immuosorbent Assay) Tests detect antibodies and are done on blood samples. Each test has its own shortcomings. The AGID Test should be used on individual animals; there are few to no false positives. The ELIZA Test is reasonably accurate but can cross-react with the bacteria that causes Caseous Lymphadinitis (CL) and give a false positive. None of these tests are 100% accurate. The ELISA Test works best as a herd-screening tool. Because antibodies appear relatively late in the disease, antibody tests in general have poor sensitivity. The ELISA Test is more sensitive, while the AGID Test is more specific, showing fewer false positives in goats which are truly negative.

The advantage of using the fecal culture positive test is that no other organism looks like Mycobacterium paratuberculosis, so false positives do not occur. It also tells other important information, such as how much of the organism is being shed. The fecal test is 40-45% accurate in light shedders; in heavy shedders, it is 95-98% accurate. Interestingly, the organism cannot be cultured in the feces of sheep.

Think of the disease as a pyramid. For every animal which tests positive, there are probably 10 animals who are infected, actively shedding, and not showing symptoms. This does not apply if an infected animal is brought into a clean, closed herd, unless the circumstance is not discovered and properly managed. Then it takes some time for this pyramid to build up, but it will occur.

There is no cure for this disease, there is nothing that can be put into the soil and the surrounding environment to kill the bacteria, and the only vaccine available is used in Norway and Iceland. The vaccine is not available in the United States because it cross-reacts with tuberculosis (TB) tests.

Managing fecal-to-oral transmission is the key to controlling Johne's Disease. Raise all feeders. Use a footbath from pen to pen. Keep manure from contact with kids. When moving feed troughs, pitchforks, water containers, and shovels from pen to pen, wash and bleach them thoroughly first. "All manure is suspect."

The good news is that Johne's Disease is not believed to be transmittable from goats to people. A higher incidence of Johne's is being seen in goats, but this may well be because more goat breeders are now testing for it. Much of the literature used in the preparation of this article was furnished by Bob Glass, President of Pan American Vet Labs, in Austin, Texas. Pan American tests for CAE and CL, in addition to providing Johne's testing. Contact them at 1-800-856-9655 for further information.

The author, Suzanne Gasparotto, hereby grants to local goat publications and club newsletters, permission to reprint articles published on the Onion Creek Ranch website under these conditions: THE ARTICLE MUST BE REPRODUCED IN ITS ENTIRETY AND THE AUTHOR'S NAME, ADDRESS, AND CONTACT INFORMATION MUST BE INCLUDED AT THE BEGINNING OF THE REPRINT. Acknowledgement must also be made that the articles were first published in GOAT RANCHER Magazine, for which Suzanne Gasparotto writes exclusively. We would appreciate notification from any clubs or publications when the articles are used. (A copy of the newsletter or publication would also be a welcome addition to our growing library of goat related information!)

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