Hepatic Mycobacterium heckeshornense 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 Mycobacterium 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 Mycobacterium heckeshornense. 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 M. heckeshornense infection in a dog. Diseases caused by non-tuberculous mycobacteria such as M. heckeshornense 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 M. heckeshornense infection and can develop life-threatening pathology affecting multiple organs. However, clinical resolution can be achieved even in a severely affected dog. If Mycobacterium is suspected, it is important to consult with diagnostic laboratories to ensure correct samples are obtained and correct analytical procedures are used.