Mycobacterium genavense detection in a blood smear from a domestic ferret

The domestic ferret is sensitive to mycobacterial infections, which are likely underdiagnosed. There are limited reports of therapy for mycobacteriosis in ferrets and most have failed. A ferret in poor body condition revealed marked organomegaly on diagnostic imaging. The complete blood count revealed a mild pseudoeosinophilia, which might be attributed to negatively stained bacilli phagocytised by monocytes observed in the blood smear. Ziehl–Neelsen stain was performed and showed acid‐fast bacilli within monocytes. Fine‐needle aspirates of the spleen and liver revealed the same finding. Mycobacterium genavense was identified by PCR and DNA sequencing from peripheral blood. Treatment with rifampicin, clarithromycin and enrofloxacin was initiated. The disseminated mycobacteriosis was suspected from the observation of bacilli on the blood smear. After 16 months, the ferret is still undergoing treatment. To prevent recurrence, continued monitoring of drug toxicity and effective therapy will be maintained even after the resolution of clinical signs (mostly organomegaly).