Nocardioform Placentitis Affecting Kentucky's 2011 Foal Crop

In November and December of 2010, the number of nocardioform placentitis cases submitted to the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) increased markedly. This increase was observed both by pathologists and through the use of a diagnostic surveillance tool monitored by the epidemiology section. The increasing incidence of nocardioform placentitis continued into 2011, causing growing concern among practitioners, farm owners, and managers, the University of Kentucky Department of Veterinary Science, and the horse industry media.

Following several meetings with stakeholders in the equine industry, an ad hoc task force was assembled to further investigate the unusual number of cases. Full participation by the equine industry--including subsidies for placental examinations by local organizations--led to the largest number of nocardioform placentitis submissions on record, more than 325 laboratory confirmed cases. Of those placentitis cases, 30% resulted in abortions or stillbirths, and 70% resulted in a live foal.

Nocardioform placentitis was first identified in central Kentucky in the mid-1980s. The term "nocardioform" was adopted due to similarities of the causative agents to the broad category of bacterial organisms called nocardioform actinomycetes. Through sequence analysis of 16S rRNA genes, the most common organisms have been identified as Crossiella equi sp., Amycolatopsis spp., and Streptomyces spp. The clinical ramifications of nocardioform placentitis range from late gestation abortions, stillbirths, and prematurity to small and weak foals that may or may not survive. Due to the fact that even mild cases of nocardioform placentitis were submitted in 2011, a number of foals were healthy and vigorous at birth even though the placenta was affected with nocardioform placentitis.

Lesions of nocardioform placentitis are distinctive. The cervical star (where the foal normally erupts through the placental membranes) region is spared. Lesions most commonly occur in the body of the placenta at the bifurcation of the horns. Most typical cases of bacterial (non-cardioform) placentitis are ascending and begin in the cervical star region. Lesions may be single or multiple. The affected chorion (the outer placental membrane) is covered by a thick, light brown, tenacious exudate (described by some as resembling peanut butter) that overlays a rough, tan chorion with marked loss of villi (essentially a type of epithelial cell). Loss of chorionic villi severely compromises fetal nutrition, leading to the characteristic emaciated appearance of most aborted fetuses. The bacteria do not cross from the fetal membranes to the fetus, another unusual feature.

In the past, theories about nocardioform placentitis have been largely limited to anecdotal observations. Common theories are that nocardioform placentitis occurs when the previous fall has been dry and that mares are affected sporadically, without any one farm having a greater number of cases in proportion to the number of mares. Nocardioform placentitis has been documented in Florida, New York, South Africa, and Italy, as well as Kentucky.

It is hoped that significant inroads can be made in the understanding of this unusual disease process through the tremendous number of cases received and with the collaboration among practitioners, owners, the UKVDL, and the University of Kentucky Gluck Equine Research Center. Currently, studies are in progress to better understand this condition, the route of infection, early diagnosis, and better means of treatment.

CONTACT: Laura Kennedy, DVM, Dipl. ACVP, 859/257-8283,, Veterinary Diagnostic Laboratory, University of Kentucky, Lexington, Kentucky

This is an excerpt from Equine Disease Quarterly, funded by Lloyd's of London underwriters, brokers, and their Kentucky agents.

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Equine Disease Quarterly

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