United States Department of Agriculture (USDA) regulations state that an organism-based test (culture/PCR) is the official test for determining the infective status of an animal for Johne's disease. Recent method evaluation tests performed for laboratory approval for the Voluntary Bovine Johne's Disease Control Program (VBJDCP) indicate multiple culture methods are being used in the United States (US). The annual evaluations indicate a wide range of sensitivities associated with the different culture methods. The National Veterinary Services Laboratories (NVSL) have been requested to establish a standardized protocol for detecting Mycobacterium avium subspecies paratuberculosis(Map) in fecal samples which is reproducible and has a known sensitivity.

The NVSL have also been requested to establish the criteria for well-characterized bovine fecal panels for use in organism-based detection procedures and methods evaluation. These panels will be used to validate different diagnostic procedures, including serological assays and USDA licensed diagnostic kits used for Johne's disease detection.

Based on the results of the last 11 years of proficiency tests for detecting Map, several methods were chosen for further evaluation. These methods included different decontamination techniques involving sedimentation or centrifugation and different media including solid and liquid which have been used by multiple laboratories. Preliminary evaluation based on proficiency test results indicate that centrifugation methods are more sensitive than sedimentation decontamination methods, and liquid media methods are faster than methods using tubes of Herrold's Egg Yolk (HEY) media with mycobactin J. More PCR methods have been introduced and evaluated by different laboratories each year. Currently the Tetracore VetAlert™ Johne's Real-Time PCR is the only USDA licensed PCR Kit available in the United States.

Varied growth performances in the solid media used with different culture methods were also noted during the last 10 check tests. Two commercial sources of HEY media available in the US were evaluated along with in-house media for growth performance. Tissue culture flasks containing the same volume of HEY media and inoculums were evaluated and shown to have isolated more Map colonies earlier in an 8 week time period than tubes containing an equal volume of HEY media.