This is an updated article on Johnes. While not much new information exists, goat producers are seeing more and more Johnes in their animals.
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. However, more cases of Johnes are being diagnosed. Goat producers in Ohio and surrounding states are seeing Johnes. Dairy cattle operations have long been fighting Johnes, and people raising goats on land that formerly housed dairy cattle are seeing Johnes appear in their goats. Pygmy goats seem to be more susceptible than other breeds, maybe because of the intensive breeding that has been done to refashion them down to smaller size with resultingly smaller immune systems.
Johnes (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. Johnes 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 Johnes 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 Johnes in utero (before birth) if their dams are heavily infected. Kids can also become infected through the colostrum and milk of Johnes-carrying mothers. This bacterium is very hardy and heat resistant. However, pasteurization can kill most (if not all) of the organisms, depending upon the concentration of the bacterium in the milk, and is a useful technique for reducing (but not eliminating entirely) the number of organisms the kids receive. The organisms 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 Johnes-infected goats usually live less than one year and ultimately die from their inability to absorb nutrients from their intestinal tracts.
The timeline roughly 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 approximately age two to four, is the really dangerous time, because those goats look reasonably well but are shedding the bacteria like crazy.
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 Lymphadenitis (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 method is that false positives rarely occur and you find out which goats are shedding the organism on your premises. 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.
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 and will not be 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 but this has not yet been established scientifically. Much of the literature used in the preparation of this article was furnished by Bob Glass, President of Pan American Vet Labs, in Hutto, Texas (near Austin). Pan American tests for CAE and CL, in addition to providing Johne's testing. Contact him at 1-800-856-9655 for further information or email email@example.com.
Suzanne W. Gasparotto (Article updated July 10, 2010)
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