Mycobacterium spp. Infections

Although laboratory mice are susceptible to experimental infections with Mycobacteria, naturally occurring infections are rare. An outbreak of M. avium-intracellulare infection in B6 mice, but not C3H/HeN or B6C3F1, has been documented.

The authors have observed similar outbreaks. Mycobacterium avium-intracellulare complex organisms can be isolated from soil, water, and sawdust, which was the presumed origin of the infection in mice. Infected mice were subclinical. At necropsy, there were a few subpleural 1-5-mm diameter tan-colored masses in lung. Microscopic findings consisted of focal accumulations of epithelioid cells, foamy macrophages, and lymphocytes in alveolar spaces and septa, with variable amounts of necrosis and neutrophilic leukocyte infiltration. Many of the mice had microgranulomas with occasional Langhans-type giant cells in liver parenchyma and mesenteric lymph nodes. Large numbers of acid-fast bacilli were visualized in some lesions. There has been a rise in interest in using the mouse as a model for nontuberculous mycobacterial infections because of their importance in AIDS patients. B6 mice have emerged as the preferred susceptible mouse strain for such studies. It is now known that B6 and BALB/c mice carry a susceptibility (Bcg^s) allele, and DBA/2 and C3H/He carry a resistance (Bcg^r) allele that is a determinant of phagocytic host defense mechanisms that control intracellular pathogen infections. Definitive diagnosis can be made by demonstrating acid-fast organisms in granulomas and isolation of Mycobacterium. Differential diagnoses for pulmonary granulomas should include M. pulmonis and C. kutscheri infections, as well as lesions associated with the administration of Freund's adjuvant.

Another form of mycobacterial infection has been reported, which involved tail infections with M. chelonae in several types of immunocompromised mice, including RAG1, T-cell receptor, and Fas^lpr null mice, as well as thymectomized mice. Lesions consisted of focal granu- lomata and osteomyelitis of the tail, resulting in grossly apparent nodular swellings.

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Source: Barthold Stephen W., Griffey Stephen M., Percy Dean H.. Pathology of Laboratory Rodents and Rabbits. 4th Edition. — Wiley-Blackwell,2016. — 384 p.. 2016

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