Signalment and History:In spring of 2011 an equine fetus and placenta were submitted to the Heeke ADDL in Southern Indiana with a history of premature abortion 5 weeks before the due date. In addition, the mare had prematurely “bagged up” (developed an udder) 1-2 weeks before the abortion occurred. Otherwise, the mare appeared to be healthy and apparently had a good appetite on the day following abortion.

Gross findings:At submission, the fetus was still enclosed within the placenta. The fetus weighed 23 kg, and crown-to-rump length was 89 cm. No gross lesions were found in the fetus. The placenta had a large (25-cm) mucosal lesion located at the distal body of the uterus, near the bifurcation of the uterine horns. The mucosa in the center of this lesion was thin and pale. At the margins, the mucosa became progressively thicker, was gray, and very friable, and was surrounded by a reddened area of hyperemia.

Microscopic findings:Histologically, the placenta had extensive areas of epithelial necrosis which were heavily infiltrated with neutrophils, and covered with a thick layer of necrotic debris. Embedded within the debris were scattered star burst-shaped granules suggestive of sulfur granules. Warthin-Starry and acid-fast stains revealed the presence of small branching filamentous bacilli within these granules. These bacilli were not acid fast, and did not stain with Brown & Brenn gram stain. No remarkable histologic lesions were present in the fetal tissues.

Morphologic diagnosis:The pathologic diagnosis in this case was necrotizing and suppurative placentitis with associated filamentous bacilli.

Laboratory findings:No bacteria were isolated from the fetal tissues. A mix of bacteria were isolated from the placental mucosa, including an “actinomycete-like organism”. Unfortunately, we were not able to further identify this organism.

Final diagnosis:Placental actinomycosis

Discussion:The gross and histologic lesions in this case are very similar to those described by Hong, et al (1993) for nocardioform actinomycete-associated placentitis. This disease has been reported multiple times over the years in Kentucky since the late 1980’s. It is rarely reported elsewhere, though there are reports of it in Florida, Ontario, and South Africa. In Kentucky, the incidence varies greatly from one foaling season to the next. According to press releases from Kentucky, the spring of 2011 had an unusually high incidence of nocardioform placentitis. I had never seen this lesion until this past spring, when I saw three different cases within a 2-week period, suggesting that Southern Indiana also experienced an unusually high incidence of nocardioform placentitis at the same time as Kentucky. As far as I can tell from the literature, no climatic or other environmental factors have been associated with outbreaks of nocardioform placentitis. We were unable to definitively identify the causative organism in our case, but a number of actinomycete-like organisms have been associated with this lesion including Crossiella equi, Amycolatopsis spp., Nocardia spp., and Rhodococcus rubropertinctus. Crossiella equi is most frequently cited as the causative agent. The location of the lesion near the uterine bifurcation (and relatively far from the cervix) is unusual for bacterial placentitis, and when placentitis is seen in this location the practitioner should strongly consider nocardial infection. This unusual location has suggested to some that infection is acquired through the blood stream and not through the cervix, but the pathogenesis of this infection has not been well-studied. As in this case, nocardioform infection is limited to the placenta with sparing of the fetus, and the placenta must be included in the diagnostic submission if a diagnosis is to be obtained. Although postpartum placentas are frequently contaminated with environmental bacteria, nevertheless, the practitioner should swab the lesion and submit it for bacterial culture with the specific request that the lab look for a nocardia-like organism.