Mycobacterium fortuitum Infection Associated With Septic Arthritis and Mycobacteremia in a Dog From Northern California

Mycobacterium fortuitum mycobacteremia and arthritis were diagnosed in a Briard dog from northern California. The dog was evaluated for lameness and had a history of immunosuppressive treatment and splenectomy for refractory immune thrombocytopenia. Cytological examination of synovial fluid from the right tarsus indicated marked suppurative inflammation with intralesional acid-fast bacteria. Mycobacterium fortuitum was cultured from joint fluid and blood; identification was based on PCR sequencing. Diagnosis was complicated by initial misidentification of the organism as an Actinomyces species. The dog was successfully treated with clarithromycin and enrofloxacin. The dog was later treated for a Grade III mast cell tumor of the thoracic limb with radiation therapy and chemotherapy and then died 2 years after the diagnosis of mycobacteremia because of extradural hemangiosarcoma of the spine.