Aspergillus spp. Infection: Aspergillosis

Pulmonary aspergillosis, caused by A. fumigatus, A. niger, and A. flavus, is primarily of historical interest, but occurs sporadically among young rabbits. Infection is often sub- clinical, with pulmonary granulomas encountered in rabbits at necropsy.

Dermatophytosis: Ringworm

Clinical cases of dermatophytosis are uncommon in domestic rabbits. Disease is usually sporadic, but can

FIG. 6.56. Lung from a rabbit kit with pulmonary aspergillosis, illustrating fungal hyphae (methenamine silver stain).

also be epizootic within a rabbitry or colony. When present, lesions are usually located around the head and ears, sometimes with secondary spread to the paws. Affected areas are typically raised, circumscribed, and erythematous, with crusted surface and hair loss. Trichophyton mentagrophytes is most frequently involved, but Microsporum canis infections have also been recog­nized in rabbits. Microscopic examination of skin scrap­ings from the periphery of lesions cleared in 10% KOH should reveal the typical arthrospores. Examination of tissue sections for the characteristic fungi and culture on the appropriate media are both useful diagnostic proce­dures in confirming the diagnosis. On histopathology, characteristic changes include hyperkeratosis, epidermal hyperplasia, and folliculitis, with mononuclear and polymorphonuclear cell infiltration. Stains such as the methenamine silver and PAS staining procedures will demonstrate the typical arthrospores infesting infected hair shafts. Differential diagnoses include seasonal “molt,” hair loss in does during nest building, “barber- ing” in group-housed juvenile rabbits, and acariasis.

Dermatophytes are readily transmitted to susceptible human contacts; thus careful screening, culling, and slaughter are recommended. If animals are to be treated, oral griseofulvin has been used with some success, but it is potentially teratogenic in pregnant does. Rabbits may harbor pathogenic dermatophytes, particularly M. canis, as an inapparent infection. Normal rabbits have also been found to be culture-positive for T. verrucosum, M. nanum, M. gypseum, M. persicolor, and M. distortum.