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A 3‐year‐old male neutered Golden Retriever with nasal swelling and lymphadenopathy was diagnosed with diffuse Mycobacterium avium infection. Treatment with 9 months of enrofloxacin, clarithromycin and rifampicin was successful, but relapsed 10 months later with lymphadenopathy, skin plaques and testicular involvement. Repeat treatment for 12 months was effective but 15 months later a second relapse responded to the same therapy which is ongoing with survival from diagnosis of 82 months. A 1‐year‐old male neutered Portuguese Podengo was diagnosed with polyarthritis and M. avium infection and treated with enrofloxacin, clarithromycin and rifampicin for 4 months but relapsed, subsequently responding to combined pradofloxacin, rifampicin, doxycycline and ethambutol. After 12 months of treatment, M. avium was detected and treatment extended to 17 months before stopping when no organism was detected. Relapse occurred after 6 weeks, responding to retreatment but relapsing (polyarthropathy, lymphadenomegaly) after 15 months, with euthanasia 38 months after diagnosis. Dogs with M. avium are challenging to treat with frequent relapse; however, long‐term survival is possible. [ABSTRACT FROM AUTHOR]

A 1‐year‐old male neutered Portuguese Podengo dog was presented for lameness, inappetence, pyrexia, diarrhoea and abdominal moderate to severe lymphadenomegaly. Cytology of synovial fluid revealed neutrophilic inflammation in multiple joints suggestive of immune‐mediated polyarthritis. Cytology of fine‐needle‐aspiration material obtained from lymph nodes revealed macrophages with intracytoplasmic, rod‐like Ziehl‐Neelsen positive staining structures, indicative of mycobacteria. Four‐month treatment with enrofloxacin, rifampicin and clarithromycin resulted in clinical improvement and resolution of polyarthritis as evidenced on repeat synoviocentesis, but diarrhoea recurred, Ziehl‐Neelsen positive organisms were again found on lymph node cytology and analysis of the 16S rRNA‐gene using the Basic Local Alignment Search Tool facility resulted in a match to Mycobacterium avium with 100% sequence identity. Treatment was adjusted to include pradofloxacin, doxycycline, rifampicin and ethambutol and 3 months later the dog is clinically normal. Based on the literature search, this is the first time canine Mycobacterium avium infection associated with immune‐mediated polyarthritis is reported. Based on scoping searches, this is the first report of canine Mycobacterium avium infection associated with immune‐mediated polyarthritis. [ABSTRACT FROM AUTHOR]