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Evaluation of microbial culture of pooled fecal samples for detection of Mycobacterium avium subsp paratuberculosis in large dairy herds

Saraya TavornpanichDepartment of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616.

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Ian A. GardnerDepartment of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616.

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Randall J. AndersonCalifornia Department of Food Agriculture, Animal Health Branch, 3800 Cornucopia Way, Ste F, Modesto, CA 95358.

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Sang ShinNew York State Animal Health Diagnostic Laboratory, Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

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Robert H. WhitlockJohne's Research Laboratory, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

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Terry FyockJohne's Research Laboratory, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.

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John M. AdaskaCalifornia Animal Health and Food Safety Laboratory System, 18830 Rd 112, Tulare, CA 93274.

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Richard L. WalkerDepartments of Pathology, Microbiology, and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616.

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Sharon K. HietalaDepartment of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616.

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Abstract

Objective—To evaluate sensitivity of microbial culture of pooled fecal samples for detection of Mycobacterium avium subsp paratuberculosis (MAP) in large dairy herds and assess the use of the method for estimation of MAP prevalence.

Animals—1,740 lactating cows from 29 dairy herds in California.

Procedure—Serum from each cow was tested by use of a commercial ELISA kit. Individual fecal samples were cultured and used to create pooled fecal samples (10 randomly selected fecal samples/pool; 6 pooled samples/herd). Sensitivity of MAP detection was compared between Herrold's egg yolk (HEY) agar and a new liquid culture method. Bayesian methods were used to estimate true prevalence of MAP-infected cows and herd sensitivity.

Results—Estimated sensitivity for pooled fecal samples among all herds was 0.69 (25 culture-positive pools/36 pools that were MAP positive). Sensitivity increased as the number of culture-positive samples in a pool increased. The HEY agar method detected more infected cows than the liquid culture method but had lower sensitivity for pooled fecal samples. Prevalence of MAP-infected cows was estimated to be 4% (95% probability interval, 2% to 6%) on the basis of culture of pooled fecal samples. Herd-level sensitivity estimate ranged from 90% to 100% and was dependent on prevalence in the population and the sensitivity for culture of pooled fecal samples.

Conclusions and Clinical Relevance—Use of pooled fecal samples from 10 cows was a cost-effective tool for herd screening and may provide a good estimate of the percentage of MAP-infected cows in dairy herds with a low prevalence of MAP. (Am J Vet Res 2004;65:1061–1070)

Abstract

Objective—To evaluate sensitivity of microbial culture of pooled fecal samples for detection of Mycobacterium avium subsp paratuberculosis (MAP) in large dairy herds and assess the use of the method for estimation of MAP prevalence.

Animals—1,740 lactating cows from 29 dairy herds in California.

Procedure—Serum from each cow was tested by use of a commercial ELISA kit. Individual fecal samples were cultured and used to create pooled fecal samples (10 randomly selected fecal samples/pool; 6 pooled samples/herd). Sensitivity of MAP detection was compared between Herrold's egg yolk (HEY) agar and a new liquid culture method. Bayesian methods were used to estimate true prevalence of MAP-infected cows and herd sensitivity.

Results—Estimated sensitivity for pooled fecal samples among all herds was 0.69 (25 culture-positive pools/36 pools that were MAP positive). Sensitivity increased as the number of culture-positive samples in a pool increased. The HEY agar method detected more infected cows than the liquid culture method but had lower sensitivity for pooled fecal samples. Prevalence of MAP-infected cows was estimated to be 4% (95% probability interval, 2% to 6%) on the basis of culture of pooled fecal samples. Herd-level sensitivity estimate ranged from 90% to 100% and was dependent on prevalence in the population and the sensitivity for culture of pooled fecal samples.

Conclusions and Clinical Relevance—Use of pooled fecal samples from 10 cows was a cost-effective tool for herd screening and may provide a good estimate of the percentage of MAP-infected cows in dairy herds with a low prevalence of MAP. (Am J Vet Res 2004;65:1061–1070)