Chronic osteoarthritis caused by <i>Propionibacterium australiense</i> infection in a captive sand gazelle

Osteoarthritis is a common cause of morbidity and mortality in geriatric gazelles. <i>Propionibacterium australiense</i> has been reported as a cause of systemic granulomas in cattle, but there are no descriptions of this bacteria infecting other species nor causing osteoarthritis, to our knowledge. An 8-y-old, castrated male, sand gazelle (<i>Gazella leptoceros leptoceros</i>) was managed for chronic, intermittent, progressive osteoarthritis of the right tarsus. Serial biopsies revealed pyogranulomatous dermatitis with intralesional bacteria. Serial diagnostic imaging identified osseous and soft tissue proliferation with draining tracts. Treatments over 1 y included broad-spectrum antibiotics, anti-inflammatories, joint debridement, and infusion with platelet-rich plasma and stem cells. Despite therapy, lameness persisted, azotemia developed, and subsequently, the animal was euthanized. On postmortem examination, the periarticular tissue of the right tarsus was markedly expanded by pyogranulomas and fibrosis. Histologically, the synovium, joint capsule, and overlying soft tissues were markedly expanded by pyogranulomas and numerous gram-positive and acid-fast-negative filamentous bacteria surrounded by Splendore-Hoeppli material. Within the joint, there was regionally extensive cartilage ulceration, osteonecrosis, osteolysis, and pannus formation. PCR assay of affected formalin-fixed, paraffin-embedded tissue amplified segments of 16S rRNA and β subunit of bacterial RNA polymerase (<i>rpoB</i>) genes with 99.7% and 95.6% identity to <i>P. australiense</i>. This bacterium should be considered a differential for chronic pyogranulomatous osteoarthritis in gazelles.