Systemic Mycobacterium smegmatis infection in a dog

A 3-year-old female Basset Hound was examined because of fever and lameness of 2 months' duration. Physical examination revealed a small cranial abdominal mass, which had an ultrasonographic appearance of a large abdominal lymph node. Cytologic examination of an ultrasound-guided fine-needle aspirate of the mass revealed a few macrophages that contained numerous linear unstained structures consistent with mycobacteria. Intracellular acid-fast bacilli were identified in an aspirate that was stained with modified Ziehl-Neelsen. Exploratory laparotomy revealed wide-spread abdominal lymphadenopathy. Histologic examination of hepatic and lymph node biopsy specimens revealed chronic granulomatous hepatitis and lymphadenitis. Acid-fast organisms isolated after bacteriologic culturing of a mesenteric lymph node specimen were identified as Mycobacterium smegmatis. Because the prognosis was poor, the dog was euthanatized.