Serodiagnosis of paratuberculosis in sheep by use of agar gel immunodiffusion

W. P. Shulaw From the Departments of Veterinary Preventive Medicine (Shulaw, Bech-Nielsen, Woodruff), Veterinary Clinical Sciences (Rings), and Veterinary Pathobiology (Getzy), College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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S. Bech-Nielsen From the Departments of Veterinary Preventive Medicine (Shulaw, Bech-Nielsen, Woodruff), Veterinary Clinical Sciences (Rings), and Veterinary Pathobiology (Getzy), College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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D. M. Rings From the Departments of Veterinary Preventive Medicine (Shulaw, Bech-Nielsen, Woodruff), Veterinary Clinical Sciences (Rings), and Veterinary Pathobiology (Getzy), College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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D. M. Getzy From the Departments of Veterinary Preventive Medicine (Shulaw, Bech-Nielsen, Woodruff), Veterinary Clinical Sciences (Rings), and Veterinary Pathobiology (Getzy), College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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T. S. Woodruff From the Departments of Veterinary Preventive Medicine (Shulaw, Bech-Nielsen, Woodruff), Veterinary Clinical Sciences (Rings), and Veterinary Pathobiology (Getzy), College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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SUMMARY

An agar gel immunodiffusion (agid) test was used over a 3-year period to examine 1,871 serum samples from sheep representing 5 Mycobacterium paratuberculosis — infected flocks and 4 flocks presumed to be uninfected. Of 1,032 sheep, 31 had positive agid test results (scoring 1 to 5), and 23 of these 31 were necropsied. Infection with M paratuberculosis was confirmed by 1 or more of the following findings: observation of typical lesions on histologic examination of sections of ileum or ileocecal lymph nodes, observation of clumps of acid-fast bacteria in mucosal smears of ileum, and isolation of the organism from feces or tissue. False-positive results on agid testing were not found in sheep from flocks known to have exposure to Corynebacterium pseudotuberculosis. Diarrhea in infected sheep was observed infrequently; chronic, severe weight loss was the most common sign observed. On histologic examination of tissues from 20 infected sheep, 16 (80%) had diffuse lesions of the ileum and 13 (65%) had acid-fast bacteria in areas of ileal inflammation; 4 had discrete granulomas and peripheral lymphocytic infiltrates in the ileum. Sheep with diffuse lesions tended to have higher mean scores on agid testing and examination for acid-fast bacteria, compared with those from sheep with more discrete lesions. Bacteriologic culture yielded M paratuberculosis from only 3 sheep with paratuberculosis. On the basis of results of this study, we suggest that the nature of the response to infection with M paratuberculosis may influence the results of diagnostic tests for paratuberculosis, and that agid testing may be useful to identify M paratuberculosis infection in sheep with chronic weight loss and in flock-screening programs.

SUMMARY

An agar gel immunodiffusion (agid) test was used over a 3-year period to examine 1,871 serum samples from sheep representing 5 Mycobacterium paratuberculosis — infected flocks and 4 flocks presumed to be uninfected. Of 1,032 sheep, 31 had positive agid test results (scoring 1 to 5), and 23 of these 31 were necropsied. Infection with M paratuberculosis was confirmed by 1 or more of the following findings: observation of typical lesions on histologic examination of sections of ileum or ileocecal lymph nodes, observation of clumps of acid-fast bacteria in mucosal smears of ileum, and isolation of the organism from feces or tissue. False-positive results on agid testing were not found in sheep from flocks known to have exposure to Corynebacterium pseudotuberculosis. Diarrhea in infected sheep was observed infrequently; chronic, severe weight loss was the most common sign observed. On histologic examination of tissues from 20 infected sheep, 16 (80%) had diffuse lesions of the ileum and 13 (65%) had acid-fast bacteria in areas of ileal inflammation; 4 had discrete granulomas and peripheral lymphocytic infiltrates in the ileum. Sheep with diffuse lesions tended to have higher mean scores on agid testing and examination for acid-fast bacteria, compared with those from sheep with more discrete lesions. Bacteriologic culture yielded M paratuberculosis from only 3 sheep with paratuberculosis. On the basis of results of this study, we suggest that the nature of the response to infection with M paratuberculosis may influence the results of diagnostic tests for paratuberculosis, and that agid testing may be useful to identify M paratuberculosis infection in sheep with chronic weight loss and in flock-screening programs.

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