Mycobacterium bovis pneumonia in an imported cat
Josepha DeLay, Mirjana Savic, Olga Andrievskaia, Felix Gwak
Animal Health Laboratory, University of Guelph, Guelph, ON (DeLay); Canadian Food Inspection Agency, Ottawa, ON (Savic, Andrievskaia); Ashcott Veterinary Clinic, Scarborough, ON (Gwak)
AHL Newsletter 2023;27(3):28.
Mycobacterium bovis was confirmed as the cause of granulomatous pneumonia in a 1-year-old Oriental Longhair cat submitted to the AHL for postmortem examination. The cat had died unexpectedly following a short period of weight loss and lethargy. Antemortem clinical evaluation and treatment had not been pursued. The cat was imported to Canada from China 4 months prior to death.
Significant gross postmortem lesions were limited to the thoracic cavity. Lungs had a diffuse mottled tan-gray color and multiple small foci of hemorrhage (Fig. 1). Lung parenchyma was firm, and lungs failed to collapse. Tracheobronchial lymph nodes were enlarged to approximately 2-3x normal size, and had a diffuse light red color on the capsular surface and upon sectioning.
Figure 1. Gross lesions of M. bovis granulomatous pneumonia in a cat. Lungs are firm, mottled tan-gray with multiple hemorrhagic foci, and failed to collapse.
Histologically, lung lesions were severe and diffuse. Aggregates of macrophages infiltrated and effaced most alveoli, obscuring normal pulmonary architecture (Fig. 2). In some sites, inflammatory cell aggregates were centered on small foci of coagulation necrosis. Small loose clusters of lymphocytes, few neutrophils, and scant fibrin were occasionally intermingled with epithelioid macrophage. Hemorrhage flooded low numbers of alveoli. In tracheobronchial lymph nodes, multiple small clusters of plump epithelioid macrophages in cortex and medulla were occasionally centered on small necrotic foci.
Figure 2. Histologic lesions of M. bovis granulomatous pneumonia in a cat. Alveoli are infiltrated and normal pulmonary architecture is obscured by large numbers of densely packed macrophages intermingled with fewer lymphocytes and neutrophils, and small necrotic foci (arrow) (H&E stain).
In lung sections stained with Ziehl-Nielsen and Fite's stains, rare faintly-staining, short acid-fast intracellular bacilli were detected in macrophages. The morphology and staining features of the bacilli were compatible with mycobacteria. No fungi were detected in lung sections stained with periodic acid-Schiff (PAS) stain.
Mycobacterial testing in lung samples from the cat was carried out by the Canadian Food Inspection Agency (CFIA). Nucleic acid of the Mycobacterium tuberculosis complex was detected in lung by PCR. The M. tuberculosis complex of organisms includes M. tuberculosis, M. bovis, and several other highly pathogenic, genetically-related mycobacteria causing similar disease conditions in animals and humans. The isolate from lung in this cat was confirmed as M. bovis by culture and subsequent speciation by a combination of biochemical tests and whole genome sequencing.
M. bovis infection in cats and other species is typically associated with ingestion of unpasteurized milk or inadequately cooked or raw meat from infected cattle. Lesions in cats most frequently involve the gastrointestinal tract and associated lymph nodes. Localization of M. bovis organisms to the respiratory tract, as in this cat, has been described in some cases. Gross lesions in this cat were unusual in the diffuse distribution of lung lesions without distinct nodule (tubercle) formation.
Increased importation of pets to Canada necessitates that veterinarians adopt a broader consideration of differential etiologic diagnoses and zoonotic risks when examining and treating these animals. Imported animals may have been exposed to pathogens that are not present in Canada. Information about an animal’s country of origin or travel history should be included in the clinical history for new patients. Veterinarians and staff should use appropriate personal protective equipment (PPE) when handling animals potentially infected with zoonotic pathogens.
M. bovis is a federally (Canada) and provincially (Ontario) reportable pathogen, and both CFIA and the Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) must be notified of detection of this pathogen. Federal and provincial public health agencies must also be notified due to the significant zoonotic risk posed by M. bovis. AHL
References
1. O’Halloran C, et al. Feline tuberculosis caused by Mycobacterium bovis infection of domestic UK cats associated with feeding a commercial raw food diet. Transbound Emerg Dis 2021;68:2308-2320.
2. Greene CE, Bunn-Moore DA. Mycobacterial infections: Infections caused by slow-growing mycobacteria. In: Infectious Diseases of the Dog and Cat, 3rd edition. Greene CE, ed. Elsevier, 2006:462-477.