Bacteroides fragilis – an overlooked cause of abortion in the mare?

Overview

• This study reports the identification of Bacteroides fragilis as a potential cause of abortion in a pregnant mare, a connection not previously recognized in equine medicine.
• The findings suggest that anaerobic bacteria like B. fragilis may be underdiagnosed contributors to equine abortion due to limited use of anaerobic cultures.

Background

• Bacteroides fragilis is a type of anaerobic, gram-negative bacterium.
• It is known to cause abortion in cattle and humans but had not been linked to abortion in horses before this case.
• Equine abortion investigations traditionally use limited anaerobic culturing, potentially missing anaerobic pathogens.

Case Description

• A mare near late-term pregnancy exhibited symptoms including purulent vaginal discharge, fever, and peripheral swelling (edema).
• Due to these signs, preterm delivery was medically induced.
• The delivered foal was weak and was euthanized shortly after birth.

Diagnostic Findings

• Necropsy of the foal and placenta showed severe inflammation (allantochoroiditis) involving the entire corpus segment of the allantochorion (placental tissue).
• Histological examination found necrosuppurative choroiditis with multiple colonies of gram-negative bacilli and lung inflammation (suppurative bronchioalveolitis) in the foal.
• Anaerobic culture of the chorion revealed a mixed bacterial population dominated by Bacteroides fragilis.

Implications

• This is potentially the first documented case linking B. fragilis with equine abortion.
• The presence of B. fragilis suggests anaerobic infections may play a more significant role in equine reproductive losses than previously recognized.
• Diagnosis of such infections requires routine inclusion of anaerobic culturing techniques in abortion investigations.
• These findings highlight the need to reconsider diagnostic protocols to better detect and understand causes of equine abortion.

Conclusion

• Bacteroides fragilis should be considered a possible abortifacient in mares, alongside its established role in other species.
• Enhanced diagnostic approaches including anaerobic cultures will improve detection of anaerobic pathogens in equine abortions.
• Further research is necessary to determine the prevalence and impact of B. fragilis and similar anaerobes in equine reproductive health.