Nocardioform Placentitis: A “Quiet” but Important Problem in Mares

The 2020 Virtual Nocardioform Placentitis Workshop featured a panel of experts sharing data to ultimately determine how to improve our understanding of the disease.

The larger the placental lesion caused by Nocardioform placentitis, the more likely the mare is to abort. iStock/Dan Brandenburg

Nocardioform placentitis, although not as common as ascending placentitis, intermittently rears its head by causing late gestational/at-term abortions and perinatal deaths. The latest surge of Nocardioform cases in Kentucky was observed during the 2020 foaling season. The incidence of Nocardioform placentitis was approximately 1-2.5% of the registered Thoroughbreds in that area, making it an important concern in the equine industry.

During the University of Kentucky’s Virtual Workshop on Nocardioform Placentitis, 15 veterinarians met to discuss their experiences and available data on this disease. Barry Ball, DVM, PhD, DACT, from the University of Kentucky’s Gluck Equine Research Center, served as the workshop leader.

Ball opened the discussion by providing a brief review of our current understanding of this unique form of placentitis.

Nocardioform placentitis, as the name implies, is associated with gram positive, branching actinomyces (bacteria), including Amycolatopsis spp, Crosiella equi, Streptomyces spp., Nocardia spp. and others.

“It is a ‘quiet’ inflammation of the placenta that does not directly affect the fetus. Instead, the damage to the fetus occurs via placental insufficiency,” said Ball.

The placentas from mares with Nocardiform placentitis have a very characteristic gross appearance. The chorionic surface of the placenta that normally has a red, velvety appearance instead has an avillous section covered with a tan, mucoid exudate. The affected region typically occurs near or at the ventral aspect of the gravid horn.

When visualized using transabdominal ultrasound during gestation (e.g., during a routine scan), large areas of separation between the chorion and endometrium are appreciated, with hyperechoic fluid filling the space between the two tissues.

Affected mares:

  • Are typically older than unaffected mares;
  • Have foals with lower birth weights (as one would expect with placental insufficiency);
  • Show premature mammary development in about 50% of cases; and
  • Do not have vulva discharge as one might see with an ascending placentitis.

“The size of the placental lesion appears to be associated with neonatal outcomes. Specifically, the larger the lesion, the more likely the mare is to abort,” Ball shared.

The importance of climate was another significant and relevant association identified from data analysis.

“An increased number of cases seems to occur following a dry, hot fall,” noted Ball. “The dry, hot conditions in August and September of 2019 preceded a dramatic increase in the number of Nocardioform placentitis cases diagnosed several months later from January through May of 2020.” 

Other than the characteristic features of the placenta and recognizing that Nocardioform microorganisms appear associated with the condition, little else regarding the pathogenesis of this disease is actually known.

“At this point, all we do know is that Nocardioform placentitis results in placental insufficiency, presenting either as late-term abortions or small, live foals usually following a dry, hot fall the year before,” Ball summarized.

Thus, one of the purposes of the Virtual Nocardioform Placentitis Workshop was for the panel of experts to relay all the data they had to ultimately determine how to improve our understanding of the disease. 

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