Bob Glock, DVM, PhD, Arizona Veterinary Diagnostic Laboratory, adds that a pet peeve as a diagnostician is when people who are looking at almost any lung abscess automatically call it Mycoplasma. “To me, these are not typical abscesses because they tend not to develop a capsule of fibrosis. They are really areas of coagulative necrosis. I see a lot of abscessed lungs that I can explain with Arcanobacterium pyogenes. I think we’ve gone overboard in looking at an abscess and declaring it a Mycoplasma.”
Tom Noffsinger, DVM, Twin Forks Clinic, Benkelman, Neb., believes more slaughter audits need to be done to help get a handle on Mycoplasma lesions. “What my treatment crews are telling me is that if we have 1,000 head of calves come through the hospital, the incidence of Mycoplasma lesions at slaughter in the calves that responded to a very short, intense treatment is low. The incidence of Mycoplasma lesions in the lungs of re-treat pens is much higher. We’re finding that those lesions were present on arrival or shortly after.”
Rosenbusch agrees. “The swine industry has learned that unless you do pre-slaughter checks, you will not get a true picture of Mycoplasma and pneumonia. I think what’s going to happen in the cattle industry is that we’re going to have to bite the bullet and necropsy a fraction of our animals at 15 to 30 days after arrival until we learn what we’re doing. It’s a big expense,” he concedes, but “we will be blind until that happens.”
Samples for diagnosis
As far as clinical diagnostics, Noffsinger has found Mycoplasma mainly by the use of PCR on lung tissues, in conjunction with aerobic and anaerobic bacterial cultures and looking for viruses, such as BVDV, in tissues. He usually submits lymph nodes and lungs when diagnosing respiratory disease.
Because of middle-ear infections in younger and veal calves, Alvin Baumwart, DVM, Highland Veterinary Clinic, Arapaho, Okla., typically sends the soupy ear or joint fluid to the lab for a diagnosis and believes the gold standard for diagnosis is culture. “I want it demonstrated in the lab before I will say it’s M. bovis,” he says.
Alvin Baumwart, DVM, believes the gold standard for Mycoplasma bovis diagnosis is culturing the organism.
Grooms adds that pathologist Ted Clark, DVM, Dipl. ACVP, from the Western College of Veterinary Medicine, recommends sending in synovial tissue, as well as joint fluid. “He thinks we get better isolation results,” says Grooms. “So we turn in not only fluid but also a piece of the synovium to help increase our yield.”
Rosenbusch prefers using the immunohistochemistry test because it gives a pathology link to a high-level presence of Mycoplasma in the lesions. “We won’t get an immunohistochemistry-positive signal unless we have 107 or 108 Mycoplasma accumulating in one location. That’s a lot of Mycoplasma in one spot.”
He says most PCRs can detect 103 or 104 organisms from a sample. “What goes into a PCR reaction is less than a tenth of a milliliter, so even if you send 10mL of ear exudate or a big chunk of lung, they’re going to sample a very small amount. So Mycoplasma has got to be there at the site of sampling or you miss out. Even with immunohistochemistry, you can section only a piece big enough to put on a 2-in. by 1-in. slide. If we sample the wrong part of the lung, we’re not going to get the immunohistochemistry signal. I think there are gross lesions that are classical enough that they can guide a pathologist or a veterinarian in the field.”
Richard Sommers, DVM, believes in necropsying as many dead animals as possible.