Infection of an equine placenta with a novel mycobacterial species leading to abortion.

This research paper covers the study of a 25-year-old pregnant horse who, despite medical treatment, had an abortion due to infection of her placenta by a new species of mycobacteria, a genus of bacteria that usually doesn’t cause much inflammatory response.

Case Presentation and Diagnosis

• The horse was a 25-year-old American Quarter Horse mare, who had developed a vaginal discharge that progressively worsened over a week.
• Ultrasound showed increased thickness of the uterus and placenta and signs of chorioallantoic edema or swelling in the chorion (outermost membrane surrounding an embryo) and allantois (a sac-like structure involved in nutrient exchange).
• Despite medical treatment, the horse had an abortion two days after initial presentation.
• Post-mortem examination revealed a thickened, brown chorionic surface in the right horn and body area of the uterus and fluid-filled sacculations on the allantoic surface of the umbilical cord, allantoamnion, and chorioallantois.
• The bacterium identified was a non-branching acid-fast organism from the Mycobacterium Runyon IV group, which was unusual as it did not trigger a significant granulomatous inflammatory response unless villar necrosis (death of cells) occurred.
• After using Ziehl-Neelsen staining that confirmed the presence of acid-fast bacteria cells, the bacteria were found to reside in areas of the gravid horn and the cervical star area.

Discovery of a Novel Mycobacterium Species

• Further analysis of the genetic material from the bacteria isolated showed that it was a new species, not previously known to science.
• The 16S ribosomal RNA gene and the rpoβ gene, which encodes the β subunit of RNA polymerase, were both sequenced, revealing the bacterium to be a rapidly growing novel species of mycobacteria.
• This new species was implicated as a potential cause of abortions in horses.

Significance and Implications

• Mycobacteria are rarely reported as a cause of placenta-related complications and abortion, but their presence in this case suggests that they should be considered when diagnosing cases of chronic placentitis that extend beyond the cervical star area.
• The findings of this research may lead to a better understanding of infectious causes of abortion in equines, as well as the development of more effective prevention and treatment strategies.