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Diagnosis | Mycobacteriosis

Lab Animal volume 35, pages 20–22 (2006)Cite this article

Mycobacteriosis in frogs and other amphibians typically presents as single or multiple, sometimes ulcerated, cutaneous and subcutaneous nodules or swellings of granulomatous dermatitis and cellulitis. Lesions can be cutaneous or systemic, or develop in combination as in this case5. The infection may be localized as a dermatitis and cellulitis, or invasive and fatal due to the presence of disseminated granulomas7. In frogs, the digital tips, digital webs, oral cavity, hindlimbs, feet and skin are the most frequent sites of infection. An infected frog may undergo wasting despite a good appetite due to the compromise of the intestinal tract and associated organs where mycobacterial granulomas have formed or due to systemic effects2. Other key clinical signs in frogs may be a moribund appearance, a coelomic effusion or septicemia. Gross pathological changes in systemic mycobacteriosis typically include multiple firm, well-circumscribed tan to gray nodules of varying sizes in the liver, kidneys, spleen, lungs, and intestinal tract. Pink to red encapsulated nodules may be present in the fore and hind limb muscles. Splenomegaly and hepatomegaly may also be present. The virulence of the mycobacteria, degree of host resistance, and the size and location of the bacterial inoculum determine the severity of the lesion8.

Other mycobacterial species known to cause opportunistic amphibian infections include M. ranae (M. fortuitum), M. xenopi, and M. ranicola8,9. These acid-fast, cold-water mycobacteria can be routinely cultured from many aquaria and are common commensals on amphibians' skin. M. ulcerans is a water-borne pathogen that causes necrotizing skin lesions5. M. chelonae was detected in a Xenopus laevis colony in association with focal, non-healing ulcerated skin wounds10.

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Figure 2: Photomicrograph of ventral mandibular skin and subcutaneous tissue of the African clawed frog in Figure 1.

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Acknowledgements

The authors gratefully acknowledge the contributions of Drs. Stephen Smith and Michael Stoskopf for their expertise in mycobacterial disinfection, and of Mr. Tornby O. Hall and Ms. Barbara Welker for their dedicated care of laboratory animals.

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Diagnosis | Mycobacteriosis. Lab Anim 35, 20–22 (2006). https://doi.org/10.1038/laban0506-20

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