The placenta and the aborted male fetus from a mature Angus cow were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for diagnostic testing. The cow had been artificially inseminated seven months prior to the abortion. No clinical signs prior to the abortion were reported in the submission form by the submitter. The fetus was fully haired and measured 54.8 cm crown to rump. On necropsy, all organs were unremarkable except for multifocal dark-red areas in the lung. The placenta was mildly thickened and had areas of mild to moderate hemorrhage and edema. On microscopic examination, the placenta was expanded with edema and had areas of inflammation that contained a significant number of neutrophils admixed with other inflammatory cell types and necrotic debris (Fig. 1 and 2). The alveolar septa and the interstitium of the lung had multifocal pockets of inflammatory cells composed primarily of macrophages and scattered neutrophils (Fig. 3).
Ancillary testing on the fetus included PCR for Neospora. caninum, Leptospira spp., Bovine Viral Diarrhea Virus, Bovine Respiratory Syncytial Virus, Bovine Parainfluenza-3 Virus, Bovine Herpesvirus-1, and Bovine Coronavirus, of which all results were negative. Bacterial culture of the fetal abomasal contents resulted in no growth. Despite the lack of bacterial growth on culture, the presence of large numbers of neutrophils in the placenta is a finding consistent with a bacterial infection. The presence of neutrophils in the fetal lung is a lesion that is often found in cases of bacteremia, likely secondary to the placentitis. Given the gross and microscopic findings in the fetus, the most likely cause for the abortion in this case is bacterial placentitis.
General bacterial placentitis in cattle is an inflammatory condition of the placenta, typically caused by ascending or hematogenous bacterial infections that may lead to spontaneous abortion. Bacterial pathogens include Arcanobacteria spp., Bacillus spp., E. coli, Histophilus spp., Pasteurella spp., Pseudomonas spp., Serratia spp., Staphylococcus spp., and Streptococcus spp. These bacteria are not believed to be contagious to other cows but rather opportunistic. These pathogens can breach the maternal-fetal barrier, resulting in inflammation of the chorion and allantois, often leading to placental thickening, necrosis, and fibrin deposition. This can happen when bacteria enter through the reproductive tract or spread through the bloodstream. Although an infection via the vaginal canal is possible, a localized infection or mucosal membrane trauma in the dam more often allows bacteria to reach the bloodstream. Once in the bloodstream, the bacteria localize to the reproductive tract where infection of the fetus occurs. Clinically, abortion, premature calving, or the birth of weak or stillborn calves may be the only apparent manifestation of the disease. At the time of abortion, lesions in the dam may or may not be present. This type of abortion can occur at any stage of gestation but is most commonly seen in the second half of gestation. Since these bacterial agents are commonly found in the environment, contamination of tissues often confounds bacteriology results (i.e. growth of mixed bacterial colonies); therefore, the culprit cannot be identified in most cases unless a pure bacterial culture is obtained (i.e. single organism growth). TVMDL offers necropsy, histopathology and bacterial culture to aid in the diagnosis of placentitis and spontaneous bacterial abortion in cattle.
References
J Vet Diagn Invest 5:64-68 (1993)