Abortion in a mare associated with Corynebacterium pseudotuberculosis infection.

The research study discusses the case of a Thoroughbred mare that aborted a 254-day-old male fetus, which was found to be associated with an infection caused by Corynebacterium pseudotuberculosis. This bacterium is known to cause ulcers and abscesses in horses and has been linked to some cases of abortion, although this study provides a detailed examination of the pathological impact of the infection on both the fetus and the placenta.

Circumstance and Symptoms

• The Thoroughbred mare had been moved from California to Kentucky only 10 days prior to the abortion, and had been found to be carrying a live fetus just a few days before.
• The mare had received standard vaccinations for influenza, EHV-4, and Streptococcus equi, and had also been dewormed.
• Necropsy was performed 12 hours after the abortion, which revealed a number of anomalies. The liver was noticeably swollen with abscesses, the lungs showed necrotic spots, and a portion of the “allantochorion” (part of the placenta) was pale and leathery.

Laboratory Findings

• Sections of multiple organs including the liver, lung, kidney, spleen, adrenal gland, heart, thymus, lymph node, allantochorion, amnion, and umbilical cord were preserved for further examination and embedded in paraffin blocks.
• The liver, kidney, lung, and allantochorion samples were tested for bacterial culture. A gram-positive bacillus bacterium was discovered. Based on the bacterium’s characteristics, it was identified as Corynebacterium pseudotuberculosis.

Implications and Significance

• The detected bacterium, Corynebacterium pseudotuberculosis, is known to cause deep subcutaneous abscesses, ulcerative lymphangitis, and internal abscesses in horses. It has been associated with some reported cases of abortion, but this study represents the first detailed description of the pathological effects of this infection on both the fetus and the placenta.
• The source of infection and how the bacterium entered the horse’s system are still unknown. Previous recorded abortions attributed to Corynebacterium pseudotuberculosis infection were believed to have arisen from primary subcutaneous or internal abscesses in the mares, but in this case, no such abscesses were noted.