Hepatic <i>Mycobacterium heckeshornense</i> infection in a dog with cavitary lung disease.

A 9-year-old neutered male cairn terrier dog was initially presented because of inappetence, increased respiratory effort, and occasional coughing. A cavitary lung mass was diagnosed using CT and removed with lung lobectomy. Histopathology of the mass revealed necrosuppurative inflammation with acid-fast rod bacteria in macrophages, with <i>Mycobacterium</i> spp. a possible cause. Routine bacterial culture of a lung-lesion swab was negative for growth. The dog improved and did not show any clinical signs for 9 mo after the surgery, at which time a second recheck CT scan and bloodwork revealed diffuse hepatopathy and peritoneal effusion. The dog was hospitalized 3 d after this recheck because of signs of acute abdomen with vomiting, melena, polyuria, and polydipsia. Cytology of liver fine-needle aspirates revealed marked pyogranulomatous inflammation with acid-fast rod bacteria in histiocytes; phylogenetic analysis of hsp65 PCR amplicons from that tissue identified sequences identical to <i>Mycobacterium heckeshornense.</i> No other bacteria were isolated on a routine bacterial culture of a liver swab. Hepatic mycobacteriosis was treated with long-term enrofloxacin, clarithromycin, and doxycycline. The dog improved slowly, and the liver enzymes returned to normal after 4 mo of treatment. This is the first reported case of <i>M. heckeshornense</i> infection in a dog. Diseases caused by non-tuberculous mycobacteria such as <i>M. heckeshornense</i> are generally not reportable due to low risk of transmission between and to humans, but the zoonotic potential warrants further research in the future. Key clinical message: Dogs without overt immunodeficiency can be at risk of <i>M. heckeshornense</i> infection and can develop life-threatening pathology affecting multiple organs. However, clinical resolution can be achieved even in a severely affected dog. If <i>Mycobacterium</i> is suspected, it is important to consult with diagnostic laboratories to ensure correct samples are obtained and correct analytical procedures are used.