Client Guidance

Valuable diagnostic information can be gained from a quantitative interpretation of the Johne's ELISA. In general, the ELISA value is a measure of the concentration of serum antibodies to Mycobacterium avium subspecies paratuberculosis (MAP). Generally, serum antibody levels increase as the infection progresses. Animals with higher ELISA values are more likely to be shedding the bacterium in milk and colostrum and be heavy fecal shedders than lower scored animals. High ELISA scored animals are also at increased risk of developing clinical Johne's disease.
Currently, there are three, USDA-certified kits available in the U.S. for the diagnostic detection of MAP-specific antibodies. The VMRD Mycobacterium avium paratuberculosis, Zoetis Paratuberculosis SERELISA kit and the IDEXX Laboratories, Inc MAP Antibody ELISA. The WVDL is currently providing and is proficiency tested using the VMRD kits for the detection of MAP specific antibodies. WVDL does not currently use the Zoetis Paratuberculosis SERELISA kit or the IDEXX Laboratories, Inc MAP Antibody ELISA kits. It is important to remember that each kit manufacturer develops proprietary reagents such as antigen and conjugates (antibodies) that may not be the same. It is possible that one serum/plasma sample could test positive with one kit, but be negative with the other. This is because the antibody in the serum/plasma may only bind the one antigen or antigenic site from one kit manufacturer, but not the other kit manufacturer’s antigen. The only way to confirm if the animal is infected with MAP is to send a fecal sample for direct PCR or liquid culture.

WVDL primarily uses the broth microdilution method for antimicrobial susceptibility testing, although
the Kirby Bauer, disk diffusion, method is still employed when needed.

High bacterial numbers in milk, calf milk replacer (CMR) or colostrum can adversely affect the health and well being of dairy calves