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Diagnosis | Bacterial pseudomycetoma

Lab Animal volume 39, pages 72–73 (2010)Cite this article

Bacterial pseudomycetoma (also known as cutaneous bacterial granuloma, botryomycosis, staphylococcic actinophytosis, granular bacteriosis and bacterial pseudomycosis) is an uncommon dermatological disease in veterinary medicine1,2. The nomenclature of the disease is not unified and can be somewhat confusing. The original name 'botryomycosis' suggests a fungal disease, which was later found to be caused by bacteria2. The term 'mycetoma' is used to describe a fungal or aerobic actinomycete disease, characterized by tumefaction of the involved tissue, formation of draining sinus tracts to the exterior of the involved area and the appearance in diseased tissues of microcolonies (variously described as grains, granules or sclerotia) of the etiological agent3. In pseudomycetoma, only tumefaction, ulceration and discharge are present3. In the human medical literature, there is a distinction between the visceral and cutaneous manifestations of bacterial pseudomycetoma4. Cutaneous bacterial pseudomycetoma has been reported in the veterinary literature in horses5,6, cattle5,7, sheep5, dogs1,2,8, cats5,8, pigs5,9, mice10, a zebra11 and a hamster12. Visceral bacterial pseudomycetoma has been reported in horses, cattle and guinea pigs13. Myocarditis has been reported in porpoises14, and there is one report of mammary disease in an elephant15.

The pathogenesis of bacterial pseudomycetoma is not well understood. It may be that the infection is introduced either by local trauma to the skin or by a foreign body acting as a nidus for the granular formation2. Subsequently, a fine equilibrium is formed between the patient's immune response and the virulence of the pathogen, resulting in its isolation without complete eradication2. In some cases, the condition can be a type of bacterial sensitivity2. The granulomas are formed because of an exaggerated immune response of the body to non-branching bacteria that form compact bacterial colonies, resulting in chronic non-healing pyogranulomatous skin lesions2,7,8. The disease is usually manifested as solitary or multiple nodules involving all skin layers and subcutis and, in rare cases, can invade nearby muscle and bone1,2,4. The lesions typically have a purulent exudate with white sand-like granules1,2.

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Figure 2: Photomicrograph (10× objective) of an affected skin biopsy sample taken from the hamster in Figure 1 stained with hematoxylin and eosin.
Figure 3: Photomicrographs (40× objective) of an affected skin biopsy sample taken from the hamster in Figure 1.

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Diagnosis | Bacterial pseudomycetoma. Lab Anim 39, 72–73 (2010). https://doi.org/10.1038/laban0310-72

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