By Doug Lyman, DVM, DACVP, Wisconsin Veterinary Diagnostics Laboratory
Bovine abortion caused by Ureplasma diversum has, for many years, been a topic of discussion and some skepticism as the organism is difficult to culture and little is known of its epidemiology in this regard. It was stated a few years ago by a state diagnostic laboratory that U. diversum ranked second only to BVD as a cause of bovine abortion. It is now safe to say that numbers of abortions caused by this organism far outnumber those caused by BVD and, perhaps, rank second only to “collective bacteria” in this regard at the Wisconsin Veterinary Diagnostic Laboratory. PCR testing has greatly facilitated diagnosis, consistently identifying the organism in placenta, abomasal contents and pools of mixed fetal tissues.
Bovine females consistently harbor the organism in nasal passages and vulvovaginal tract while it is found in the prepuce and semen of males and is often shed in urine (at least in females). It is often stated to be associated with embryo transfer fluids and is known to survive freezing.
While much remains to be learned of the epidemiology of U. diversum, it is known that many strains exist and disease likely occurs with exposure of naïve populations to emergent or virulent strains. While disease most often takes the form of abortion, embryonic deaths, weak calves and outbreaks of granular vulvitis are also known to occur. An additional, but little known manifestation is the occurrence of destructive bone and joint lesions in fetuses, indicating a tropism for joints. More on that later. U. diversum characteristically infects the bovine amnion and allantois, with minimal to no involvement of chorionic villi, which would seem to suggest an ascending, trans-cervical route of infection, as is known to be the case in human females infected with Ureaplasma urealyticum.
A “typical” abortion outbreak in dairy herds involves clusters of several to many abortions over the course of weeks, which can affect heifer only groups or groups of older cows. Fetuses are typically fresh and rarely younger than six months with most being third trimester. More often than not, gross lesions are not found but can include amnionitis with remarkable thickening, opacification and inflammation of the membrane. Similar changes may be seen on the allantoic surface of the allantochorion. As mentioned, severe, erosive and pitting arthritis with synovitis can be seen, most commonly affecting stifles, hips and shoulders and not necessarily bilaterally. Tissue fragments from affected joints are strongly PCR positive. See gross photo. Common histopathologic lesions include mild, suppurative bronchopneumonia with a light to moderate scattering of neutrophils in bronchioles and smaller airways. See photo. Placentitis involving the allantois, with little to no involvement of chorionic villi, is also common as is vasculitis of placental blood vessels. See photo.
Establishing a firm diagnosis of abortion is often challenging and ideally needs to include moderate to strongly positive PCR readings on placenta, abomasal contents and a pool of fetal tissue that includes lung. These, along with corroborating gross and/or histologic lesions, should establish a reasonably strong diagnosis. The situation often becomes complicated by moderate to weak placental PCR readings that occur as a result of contamination by resident organisms, which is a very common occurrence. Weakly positive fetal tissue pools that lack lesions also often confuse the diagnosis.
Fetal necropsy should include examination of hips, stifles, shoulders and placenta, including amnion if possible. Diagnostic lab submissions should include material from joints if any, placenta with amnion if possible, abomasal fluid and major fetal organs.
For related information on diagnosing uncommon diseases, see these articles on BovineVetOnline: