Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract Only
Publication Acceptance Date: 10/22/2004
Publication Date: 10/22/2004
Citation: Robbe Austerman, S., Stabel, J.R., Palmer, M.V. 2004. Evaluating the accuracy of the ifn-gamma elisa and the skin test to detect mycobacterium avium ssp. paratuberculosis (map) infection in sheep [abstract]. American Association of Veterinary Laboratory Diagnosticians. p. 87.
Technical Abstract: Diagnostic tests for Johne's disease in sheep typically identify animals shedding organisms and/or in the advanced stages of disease. Positive test results usually can be relied upon, however, negative test results tell very little about the true infection status of the animal. None of the current diagnostic tests available are accurate at diagnosing young replacement lambs or animals in the early stages of infection. The overall objective of this study is to evaluate the accuracy of skin test and IFN-gamma ELISA (Bovigam, Biocor Animal Health, Omaha, NE) to detect MAP infected sheep before they become infectious and also to accurately identify uninfected sheep. Tissue culture and/or histology were used as a gold standard. Materials and Methods A cooperative agreement was formed with four flocks with confirmed Johne's disease. These flocks had annual death loss due to Johne's disease from 0% to 10%. All breeding and replacement sheep greater than 6 months of age were tested two times a year. Tests conducted include the IFN-gamma, skin test, fecal culture, ELISA and AGID. All sheep testing positive on either fecal culture, ELISA or AGID were removed from the flock, euthanized and examined. Sheep testing positive on the INF-gamma or the skin test were allowed to stay in the flock until a second positive test. Once an animal tested positive twice, it was removed and euthanized. A total of 80 sheep were submitted and necropsied. Four tissues, ileocecal valve, ileum, distal jejunum and distal jejunum lymph node, were cultured and a total of 11 tissues were taken for histology. Preliminary Results Currently histology is identifying 55% of sheep with MAP isolated from tissues. All sheep that are histology positive are culture positive. Seventy-three percent (16/22) of the sheep removed due to skin test and IFN-gamma positive test results are tissue culture positive. Three were fecal culture positive. Over 30% of the sheep that tested positive on the skin test or the IFN-gamma are negative on the next test 6 months later. A large enough sample size of these animals has yet to be collected to evaluate infection status. Further results will be presented.