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ORIGIN: United States

Extension Goat Handbook

This material was contributed from collections at the National Agricultural Library. However, users should direct all inquires about the contents to authors or originating agencies.

DOCN 000000066
NO G-12
D. M. Sherman; U. of Minnesota, St. Paul
S. B. Guss; Pennsylvania State U., University Park
Health and Disease Management

1 Johne's disease, also known as paratuberculosis, is an infectious contagious disease of ruminant animals affecting primarily the digestive tract. The causative bacterium, Mycobacterium paratuberculosis localizes in the wall of the intestines, producing an inflammatory response which disrupts normal digestion and absorption of nutrients. This leads to chronic progressive weight loss with eventual debilitation and death. This disease was first recognized in cattle in 1895, and in goats in 1916. Since the disease has been studied more intensively in cattle, many aspects of the bovine disease have been assumed to hold true for goats. Following are the differences and similarities between goats and cattle discussed in terms of transmission, clinical signs, postmortem lesions, laboratory diagnosis and control.

2 Transmission The organism causing Johne's disease is passed in the manure of infected animals and contaminates the environment. Ingestion of contaminated feed and bedding is the most common mode of transmission. It has been shown that cattle are most susceptible to infection as very young calves and individual animals become more resistant to infection as they grow older. This is confusing from the standpoint that cattle do not show signs of the disease until they are at least two years of age. Apparently, they carry the infection in a dormant state until some stress, such as calving, triggers the onset of clinical signs. This same mode of transmission appears to hold true also for goats.

3 However, it has been suggested but not proven, that individual goats may be susceptible to new infections throughout life, if the level of environmental contamination is sufficiently high. At least in cattle, there is evidence that occasionally, infected dams may transmit the disease to offspring in utero, with the result that newborns are already infected.

4 Clinical Signs Johne's disease in cattle is characterized by the appearance of a chronic, profuse, watery diarrhea. A typical Johne's cow is three to five years of age. Often, the onset of diarrhea follows some stress such as calving, transport or concurrent disease. The diarrhea which occurs may continue intermittently or constantly for several weeks to months. During this period the cow maintains a good appetite. Despite her willingness to eat, however, the animal progressively loses weight and may appear as a walking skeleton as death approaches.

5 In goats, diarrhea is rarely a prominent sign. If it occurs at all, it is usually in the terminal stages after a prolonged period of weight loss, lack of appetite and depression. This absence of diarrhea makes the diagnosis of caprine Johne's disease difficult. Animals showing progressive weight loss should be suspected of having Johne's disease. However, heavy parasitism, chronic viral arthritis, internal abscesses, chronic pneumonia, and an inadequate ration should also be considered in the differential diagnosis. Herd outbreaks of diarrhea are not likely to be Johne's disease. Salmonellosis, Coccidiosis, Exterotoxemia and grain overload are more likely causes of diarrhea in goats. Whereas the typical Johne's goat is also an adult animal, terminal cases have been seen in goats as young as fourteen months of age.

6 Postmortem Examination Any animal dying after a period of weight loss should be subjected to a thorough postmortem examination by e.g., the state diagnostic laboratory. This helps establish the existence of Johne's disease in a herd.

7 It should be remembered that the extent of grossly visible lesions is variable in animals infected with Johne's disease. It is essential that microscopic examination of selected tissues be performed using special acid-fast stains to reveal the presence of the Johne's organism. If tissues are to be submitted by the local veterinarian to a pathology laboratory, these should include sections of ileum, cecum, ileocecal valve, ileocecal lymph node and enlarged mesenteric lymph nodes, if present.

8 There is sometimes a thickening and roughening of the wall of the small intestinal tract (especially the posterior portion), the colon and cecum. A more consistent finding is an enlargement of the iliocecal-colic lymph node as well as the other mesenteric lymph nodes. When the latter are cut, they appear necrotic (consistency of cooked oatmeal), edematous (wet and swollen) and sometimes irregularly reddened. Microscopic examination of the intestinal wall and lymph nodes reveal the proliferation of epitheloid cells and the presence of macrophages. This is called a granulomatous inflammatory reaction. When the sections are stained by an ''acid-fast'' method, the small organisms are stained red and can be seen within the epithelioid cells and macrophages. There are sometimes secondary lesions of amyloid and fibrinoid degeneration in the kidney, adrenal glands and mammary glands.

9 As far as gross lesions are concerned, there are differences between the cow and the goat. Cows may show a dramatic thickening of the intestinal wall causing the lining of the intestine to be thrown up into accordian-like folds. Goats almost never exhibit this lesion, and at best, may show only some lymph node enlargement. Appropriate tissues should always be submitted for histopathological examination if the history suggests Johne's disease, since the presence of gross lesions is unreliable in the goat.

10 Diagnosis There are two major problems associated with the successful control of Johne's disease. First, it is peculiar to this disease that for every clinically affected animal in a herd, there are probably several animals which are infected but not showing clinical signs. These are termed subclinical carriers, and they are the major source of ongoing environmental contamination and transmission. The second problem is that there is no rapid, reliable, inexpensive test for identifying these subclinical carrier animals.

11 The current diagnostic method of choice is the bacterial culture of feces on specialized media. Unfortunately, the causative agent, Mycobacterium paratuberculosis is a finicky organism, is hard to grow on artifical media, culturing takes about 14 weeks but can take as long as twenty weeks for colonies to appear. This makes the process of identifying and removing infected animals from the herd a painfully slow task. In addition, the number of organisms shed in the feces of infected animals may vary with time, meaning that several attempts at fecal culture may be necessary before an infected individual is finally identified as a shedder. The results of intradermal injection of Johnin are inconsistent; however I.V. injection of infected animals will often give a body temperature elevation of 1.5 to 3F (but stay below 103.1F) and it will double the blood neutrophil to lymphocyte ratio.

12 Many other diagnostic tests have been tried in both cattle and goats with little success. These include skin testing, the complement fixation test and the hemagglutination test. All suffer to a greater or lesser extent from the same problem. Many infected animals are missed and many noninfected animals are falsely identified as infected.

13 There may be some good news for the goat industry in the diagnostic application of the agar gel immuno-diffusion test (AGID). This test involves the formation of a precipitation line in semi-solid media (agar) between wells containing an extract of the causative organism and antibodies against the organism present in the serum of infected goats. Surprisingly, the test has been of little value when applied to the diagnosis of Johne's disease in cattle but appears to be quite accurate when applied to goats and sheep. Both clinical and subclinical goat cases can be identified with an accuracy equal to the fecal culture test. The test is inexpensive, requires a small serum sample from each animal and can yield results in only 24 hours. Though currently not an accepted diagnostic test, AGID has potential for future widespread application in the diagnosis of caprine and ovine Johne's disease.

14 Treatment and Control Unfortunately there is no satisfactory treatment available against Johne's disease. Because the causative agent is in the same bacterial genus as the organism causing tuberculosis, various antitubercular drugs have been employed, but with little or no success.

15 Vaccination holds some promise for control, but several pitfalls have obstructed progress in this area. Large draining nodules may form at the vaccination site. These are especially objectionable to owners of show animals. In addition, vaccination may cause false positive reactions to the tuberculosis skin test, thus interferring with tuberculosis regulatory programs. At present, state controlled cattle vaccination programs are underway in several states but vaccination has not been approved for use in goats.

16 Regulatory attitudes vary from state to state concerning the identification and control of Johne's disease. Some states have a voluntary control program whereas others may have mandatory controls. Regulations concerning Johne's disease in goats may be less clearly defined than those concerning cattle. It is best to check with the livestock regulatory agency in your state to acquire accurate information concerning the status of this disease.

17 Control programs may be aimed at identification of infected individuals coupled with rigid culling of animals identified as positive. At present, identification is achieved by fecal culture. Improved diagnostic techniques such as AGID can accelerate the identification process. Along with identification and culling, improved management and sanitation will help reduce the incidence of new infections. Kids should be taken immediately from does and raised in separate quarters. Before removing, kids should receive colostrum by bottle or by nursing a thoroughly washed udder to limit oral contamination. Because of the likelihood that adult goats may infect each other, animals should not be overcrowded, manure should not be allowed to build up and feed and water should be provided in such a way that fecal contamination is kept to a minimum. When possible, herd additions should be purchased from known, Johne's free herds. If the status of a herd is not known purchased animals should be quarantined for several weeks before entering the new herd.

18 At the present time, many goat owners are resigned to living with Johne's disease because of the frustration associated with trying to eliminate it from their herds. Hopefully, continued progress in understanding the mechanisms of this disease along with improved methods of diagnosis and treatment will allow us to develop a more aggressive attitude toward this aggravating problem.

ORIGIN;United States


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