Client Guidance

In a real time PCR assay a positive reaction is detected by accumulation of a fluorescent signal. The CT (cycle
threshold) is defined as the number of cycles required for the fluorescent signal to exceed background levels and
cross a pre-set threshold. CT levels are inversely proportional to the amount of target nucleic acid detected in the
sample (i.e., the lower the CT level the greater the amount of target nucleic acid in the sample).
WVDL real time assays undergo 40 cycles of amplification.

Culturing bulk tank milk (BTM) to monitor milk quality has limitations based on the amount and frequency of sampling and the amount and types of microorganisms isolated. Samples taken over days or weeks are most helpful to understanding a problem. BTM culturing can provide information about the presence or absence of a bacterial group and the identity of predominate bacterial group(s). BTM results are most useful when examined along with other records such as somatic cell counts (SCC), clinical mastitis incidences, environmental conditions and other information. BTM cultures are not a substitute for quarter milk samples. Additionally, milk samples must be collected aseptically and immediately stored on ice in order to provide valid information upon culture.

Neospora caninum is a major cause of abortions in cattle. First recognized in 1988, and linked to dogs in
1998, this parasite causes an infection called neosporosis. Studies have shown that at least half the dairy
and beef herds in the United States have one or more animals that have been exposed. In an infected
herd, up to 30 percent of the animals may test positive, and some cows may abort several times. With
good herd management, though, you can reduce this drain on your profits.

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.