Response to treatment, relapse and outcome of two dogs treated for Mycobacterium avium infection

V. Coates, S. Taylor, C. D'Aout, C. Sanchez Jimenez, C. O'Halloran

Background

Mycobacterium avium, part of the non-tuberculous mycobacteria complex, causes opportunistic infections in dogs and has a typically poor prognosis due to systemic involvement. This report details the treatment, relapse, and outcomes of two atypical canine cases, highlighting the complexity of managing Mycobacterium avium infections with multidrug therapy.

Methods

Two cases were described:

-A 3-year-old male neutered Golden Retriever with nasal swelling and lymphadenopathy treated with enrofloxacin, clarithromycin, and rifampicin over multiple relapses.

-A 1-year-old male neutered Portuguese Podengo with polyarthritis and systemic M. avium infection treated with a combination of antibiotics including enrofloxacin and later modified to include pradofloxacin, doxycycline, and ethambutol due to relapse.

Diagnosis relied on clinical findings, imaging, and PCR testing for M. avium DNA. Treatments were monitored via clinical remission, imaging, and PCR outcomes.

Results

Case 1: Despite multiple relapses after treatment cessation, the Golden Retriever achieved long-term survival (82 months) with ongoing antibiotic therapy. Initial treatments led to remission, but relapses necessitated retreatment. The current condition is stable with treatment.

Case 2: The Portuguese Podengo had a shorter survival (38 months), with recurrent relapses and euthanasia after failing to achieve sustained remission despite aggressive multidrug therapy.

Limitations

Both cases represent unique presentations and responses to treatment, limiting generalizability. Long-term survival data are sparse, and reinfection versus recrudescence could not be definitively distinguished. PCR, while useful, cannot differentiate between live and dead bacteria, complicating treatment duration decisions.

Conclusions

Dogs with M. avium infections may achieve long-term survival with aggressive multidrug therapy, though relapses are common, and eradication remains unlikely. Treatment necessitates significant commitment, and ethical considerations about prolonged antibiotic use and zoonotic risks should be communicated to owners. Further research is needed to refine diagnostic and therapeutic approaches.

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