Diagnostic Aids

Klebsiella species are Gram-negative coliform bacteria that can cause mastitis, leading to significant economic losses on dairy farms. K. oxytoca and K. pneumoniae are the species that are responsible for causing clinical mastitis.

Streptococcus dysgalactiae – This gram positive, beta-haemolytic, coccal bacterium can be spread from cow-to-cow or acquired from the environment. Good hygiene and mastitis control programs including post-milking teat disinfection, antibiotic dry cow therapy and maintaining a clean, dry environment will reduce infections caused by this pathogen.

Streptococcus uberis – This gram-positive bacterium is the most frequent cause of mastitis in lactating cows. It can be isolated from the udder, skin, lips, and genital area of dairy cows, but infections are typically acquired from the environment. This bacterium causes mastitis during the dry period and are isolated frequently from cows with clinical mastitis during early lactation. Good hygiene and mastitis control programs including post-milking teat disinfection, antibiotic dry cow therapy and maintaining a clean, dry environment will reduce infections caused by this pathogen.

Other Streptococcus species isolated less frequently include the following:
S. acidominimus, S. alactolyticus, S. canis, S. zooepidemicus, S. equi, S. equinus (formally S. bovis), and S. parauberis.

Enterococcus species – Enterococcus species are a gram-positive cocci and lactic acid bacteria. Species include E. durans, E. faecalis, E. faecium, and E. saccharoluticus. These bacteria cause clinical and subclinical mastitis infrequently. Cows are infected from environmental contamination. Effective mastitis control procedures as mentioned above will control these mastitis-causing pathogens.

Leptospirosis is an important infectious disease of dogs. In the Midwest, Leptospirosis is usually
diagnosed in the late summer to fall time period especially if there is a sustained period of above
normal precipitation 1–3 months earlier. It is important to remember that all breeds and life
styles (city vs. rural) dogs are at risk of contracting Leptospirosis, but adult male dogs that spend
a considerable amount of time outdoors are at greatest risk

The Microscopic Agglutination Test (MAT) is the standard serological test used in the United States for diagnosis of Leptospirosis. The following six serovars are used in the assay: L. bratislava, L. canicola, L. grippotyphosa, L. hardjo-bovis, L. icterohaemorrhagiae and L. pomona. Generally, the serovar with the highest titer is the infecting serovar but cross-reactions do occur albeit at a lower level. Titers should be interpreted in the context of clinical findings, laboratory data and Leptospirosis vaccination history

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.

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