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Bulk Milk Testing for Johne’s Disease Detection at the Farm Level
Warren Foshaug1, Heather Donohue1, Jason Lombard2, Todd Byrem1 and Preetha Biswas1
(1) Antel BioSystems, Lansing, MI 48910
(2) National Animal Health Monitoring System (NAHMS) USDA:APHIS:VS:CEAH, Fort Collins, CO 80526
Johne’s disease (JD) is caused by Mycobacterium avium subspecies paratuberculosis (MAP), which invades the small intestine causing chronic enteritis in ruminants. MAP organisms are shed by infected cows in milk as well as feces. Developing a sensitive and convenient herd screening protocol to detect JD will improve the efficiency of monitoring and implementing disease control measures. This study investigated the performance of bulk tank milk testing as a convenient and cost effective screening tool to detect the level of infection in dairy herds. This study was conducted as part of the National Animal Health Monitoring System (NAHMS) Dairy 2007 Study in response to prioritization of bulk milk analysis by the Johne’s Committee of the United States Animal Health Association.
Dairy farms (n=515) were stratified into culture-positive (n=384) and culture-negative (n=131) based on results from six pooled environmental fecal samples cultured on Herrold’s egg yolk media. Bulk tank milk samples were analyzed by real-time PCR using the IS900 sequence to detect the presence of MAP organism, and by indirect ELISA to test for the presence of MAP-specific antibodies. The milk ELISA detected MAP antibody in 207 (199 were culture-positive) bulk tank samples with estimated sensitivity and specificity of 51.8% (95% CI = 46.8, 56.8) and 93.9% (89.8, 98.0) respectively. The milk real-time PCR assay detected the presence of MAP organism in 161 (153 were culture-positive) bulk tank samples with estimated sensitivity and specificity of 39.8% (34.9, 44.7) and 93.9% (89.8, 98.0), respectively. When both assays were employed in a parallel analysis, the estimates of sensitivity and specificity for bulk tank analysis were 63.6% (58.8, 68.4) and 87.8% (82.2, 93.4), respectively. The convenience of bulk tank sample collection and the rapid turnover of the ELISA assay offer an attractive mechanism to evaluate dairy herds for the presence for MAP infection. Additionally, the results from the real-time PCR assay indicate that shedding and/or contamination of MAP into milk on US dairies (31.3% of these samples) may be a more frequent occurrence than previously recognized, suggesting additional efforts to evaluate the quality of the milk supply are warranted.
Non-technical summary:
Bulk milk samples from 515 farms were analyzed to investigate if milk testing can be employed as a quick screening tool to detect the level of JD infection on dairy farms. The results indicate that analysis by bulk milk ELISA and/or real-time PCR assay correlated closely to environmental fecal analysis, and if implemented, a bulk tank test for JD would greatly reduce the cost and labor requirements of an industry-wide screening program.“A formal quality assurance program will provide greater consistency in testing procedures,” stated Todd Byrem, Ph.D., Director of AntelBio. “By incorporating guidelines and procedures for ELISA testing into their program, National DHIA will be able to quickly adopt and implement new testing programs as they become available.”
Contact information:
Name/Title: Dr. Preetha Biswas Organization: Antel BioSystems Inc. Mailing address: 3655 Forest Road, Lansing, MI 48910 Email address: biswasp@antelbio.com |
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