Submitted to: International Colloquium on Paratuberculosis
Publication Type: Abstract only
Publication Acceptance Date: 5/11/2005
Publication Date: 8/14/2005
Citation: Robbe Austerman, S., Stabel, J.R., Palmer, M.V., Oconnor, A. 2005. Comparing the probability of map tissue culture positivity in cmi negative and emi positive sheep [abstract]. International Colloquium on Paratuberculosis. p. 570. Interpretive Summary: Our objective was to evaluate the accuracy of the skin test and gamma interferon ELISA for Johne’s disease. We used an antigen that had a false positive rate in flocks without Johne’s disease of 7% for the skin test and 4% for the gamma interferon. The skin test identified 84% of the infected sheep and the IFN-gamma ELISA identified 87% of the sheep. But we could not find the infection in almost half of the sheep that were skin test positive and 2/3 of the sheep that were IFN-gamma ELISA positive. Sheep that were skin test positive were 4 times more likely to have Johne’s disease and sheep that were IFN-gamma ELISA positive were 7 times more likely to have Johne’s disease.
Technical Abstract: Our objective was to evaluate the sensitivity and specificity of a previously defined antigen and calculate the relative risk of CMI positive sheep in MAP tissue culture positive sheep.A johnin PPD (NVSL lot 0201) was evaluated in 2 non-infected sheep flocks (288 sheep) and found to have a skin test specificity (Sp) of 93.1 (95% CI 89.5-95.7) and a IFN-gamma ELISA Sp of 96.5 (95% CI 93.7-98.3). This PPD was then used for skin testing and the IFN-gamma ELISA every 6 months for three years in 4 MAP infected flocks. During the study period, sheep that tested positive twice on skin test and all culled sheep, greater than 6 months of age, were submitted for tissue culture for MAP. 95 sheep were evaluated, 31 were tissue culture positive, 64 were tissue culture negative. Using tissue culture as the reference test, the final skin test prior to culling had Se of 84% (95% CI 66-96) and Sp of 56 (95% CI 43-69). The IFN-gamma ELISA had Se of 87 (95% CI 70-96), and Sp of 70% (95% CI 58-82). The prevalence of tissue culture positive animals was substantially higher among skin test positive sheep (48%) compared to the prevalence of tissue culture positive animals among skin test negative sheep(12%) (Relative risk: 4, 95% CI: 2,9). The prevalence of tissue culture positive animals was substantially higher among IFN-gamma positive sheep (59%) compared to the prevalence of tissue culture positive animals among skin test negative sheep (8%) (Relative risk: 7, 95% CI: 3,19).