Non-tuberculous Mycobacteria can Cause Disseminated Mycobacteriosis in Cats

Abstract

Mycobacteriosis caused by non-tuberculous mycobacteria (NTM) is a rising concern in human medicine both in immunocompromised and immunocompetent patients. In cats, mycobacteriosis caused by NTM is considered mostly to be a focal or dermal infection, with disseminated disease mostly caused by Mycobacterium avium. We describe three cases of disseminated mycobacteriosis in cats, caused by Mycobacterium malmoense, Mycobacterium branderi/shimoidei and M. avium, with no identified underlying immunosuppression. In all cases, extracellular mycobacteria were seen in the pulmonary epithelium, intestinal lumen and glomerular tufts, which could affect the shedding of the organism. The present study highlights the importance of mycobacteriosis as a differential even in immunocompetent animals. Considering the close relationship of owners and pets and the potential presence of free mycobacteria in secretions, cats should be considered as a possible environmental reservoir for mycobacteria.

Keywords: cat; mycobacteriosis; non-tuberculous mycobacteria.

Fig. 1

(A) Severe diffuse hepatomegaly (cat A). (B) Mesenteric mass (cat B), approximately 16 × 18 × 15 cm, soft and pale, weighing 500 g. (C) Severe lymphadenomegaly of the retropharyngeal lymph nodes (cat C). (D) Cytology of the mesenteric mass (cat B) showing markedly distended macrophages, giant cells and numerous unstained rod-shaped bacteria within the macrophages intra- and extracellularly. MGG.

Fig. 2

(A) Adrenal (cat A), showing a large area of necrosis with surrounding histiocytic infiltration and scattered giant cells. HE. Inset: closer view of the histiocytic infiltration. HE. (B) Abdominal mass (cat B), showing marked infiltration of enlarged macrophages. HE. Inset: high-power view of the diffuse histiocytic infiltration. HE. (C) Liver (cat C), showing multifocal nodular granulomas. HE. Inset: high-power view of a granuloma. HE. (D) Lung (cat B), showing multifocal large histiocytes within the alveolar walls. HE. Inset: acid-fast rods within the histiocytes and free in the alveolar space. ZN. (E) Kidney (cat B), showing mild basement membrane thickening in the glomeruli and multifocal aggregates of histiocytes within the glomerular tufts. HE. Inset: acid-fast rods within the glomerular tufts. ZN. (F) Small intestine (cat C) with focal epithelial ulceration. HE. Inset: numerous acid-fast rods within the ulcerated villus and free in the intestinal lumen. ZN.