Field evaluation of tracer sheep for the detection of early natural infection with Mycobacterium avium subsp paratuberculosis

Australian Veterinary Journal
Leslie A ReddacliffRichard Whittington

Abstract

To determine whether tracer sheep could be used to detect S strain Mycobacterium avium subsp paratuberculosis on pasture, and to provide further insight into the early stages of infection. A field study on two farms in an endemic area for ovine Johne's disease in New South Wales. Procedure Lambs, weaners and adult ewes were introduced to pasture with varying amounts of M. a. paratuberculosis contamination and monitored using skin tests, gamma interferon assay, faecal culture and serial necropsy of small groups for up to 15 months after first exposure. Culture from tissues was the most sensitive method for detecting early infection in sheep after natural exposure to S strain M. a. paratuberculosis. The organism was detected in at least one introduced sheep from every exposed group, 6 to 12 months after first exposure. Histopathological lesions were detected in only 17% of culture-positive sheep, and only after at least 8 months of exposure. Similarly, antemortem diagnostic tests had low sensitivity during the early stages of naturally acquired infection. There was no evidence of any differences in infection rate between sheep first exposed as neonates, as weaners or as adults. A higher proportion of lambs born to ewes from an in...Continue Reading

References

Feb 1, 1994·Journal of Comparative Pathology·R A JusteJ J Badiola
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Jul 10, 1998·Veterinary Immunology and Immunopathology·I Begara-McGorumD G Jones
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Oct 16, 2003·Veterinary Microbiology·L A Reddacliff, R J Whittington
May 7, 2004·Applied and Environmental Microbiology·Richard J WhittingtonLeslie A Reddacliff

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Citations

Oct 26, 2011·The Veterinary Clinics of North America. Food Animal Practice·Suelee Robbe-Austerman
Apr 1, 2011·Veterinary Immunology and Immunopathology·Richard J WhittingtonAuriol C Purdie
Feb 6, 2010·European Journal of Applied Physiology·R C PritchettA T Del Pozzi

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