Intestinal Mycobacterium avium Infection in Pet Dwarf Rabbits (Oryctolagus cuniculus).

Mycobacteriosis has been rarely described in pet rabbits (Oryctolagus cuniculus). Here we present two cases of intestinal mycobacteriosis from north-eastern Germany. The first adult rabbit was euthanized due to severe cardiovascular failure, hypothermia and chronic weight loss. Necropsy revealed cachexia and a focal, fibrinonecrotic lesion in the caecum. Histologically, severe granulomatous inflammation, with numerous multinucleated giant cells and abundant acid-fast bacilli, was detected under the fibrinonecrotic material in the abdominal wall adjacent to the caecal lesion, caecal lymph nodes, spleen, liver and lungs. Microbiological culture detected Mycobacterium avium subspecies hominissuis, Escherichia coli, Clostridium disporicum and Bacteroides ovatus. A retrospective assessment of 2,013 other pet rabbit necropsies, performed between 1995 and 2019, revealed one additional case of intestinal mycobacteriosis. This animal had been euthanized due to persistent hindlimb lameness and necropsy revealed comminuted fractures of the pelvic bones and multiple large liquefied abscess-like lesions in the caecal and colonic walls. Histology revealed granulomatous inflammation with acid-fast bacilli. Polymerase chain reaction on formalin-fixed, paraffin-embedded tissue identified the presence of M. avium spp. In contrast to European wild rabbits (Oryctolagus cuniculus) from Scotland, these findings indicate that intestinal mycobacteriosis is rare in pet rabbits from north-eastern Germany. Zoonotic potential should be considered due to the close contact between pets and their owners and the chronic course of the disease with an initial lack of clinical signs.