Detection of Mycobacterium avium subspecies paratuberculosis in Swiss dairy cattle by real-time PCR and culture: a comparison of the two assays

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Abstract
Aims: To compare the two different diagnostic assays for the detection of Mycobacterium avium ssp. paratuberculosis, the aetiological agent of paratuberculosis. Methods and Results: Faecal samples were derived from 310 cows, representing 13 commercial dairy herds in various locations in Switzerland with expected increased risk because of a past history of disease. Detection assays for M. avium ssp. paratuberculosis were culture (gold standard) and a newly designed real‐time PCR. Real‐time PCR identified 31 of 310 animals as positive within this risk population whereas culture identified 20 positive animals. The specificity of real‐time PCR was confirmed by DNA sequencing of the PCR product. Depending on the test used, the paratuberculosis prevalence in our tested risk population ranged from 6·5 to 10%. Conclusions: Real‐time PCR and culture data were in good agreement, and real‐time PCR generates data in a short time in contrast to culture. Significance and Impact of the Study: We consider real‐time PCR as a suitable alternative method to culture for the detection of M. avium ssp. paratuberculosis in a national surveillance programme.