Cutaneous Dermatophilosis in a Meadow Jumping Mouse (Zapus hudsonius)

A laboratory-housed, wild-caught, subadult, male meadow jumping mouse (Zapus hudsonius) presented with extensive scaling of the face, limbs, and tail and severe edema of the paws. Postmortem examination revealed marked distal limb edema with focal digital hematomas and white scales, scabs, and crusts affecting the majority of nonhaired skin. Histopathologic analysis revealed severe, multifocal, chronic-active exudative and proliferative dermatitis characterized by multilaminated crusts covering the epidermis. The epidermis was expanded by hyperkeratosis, acanthosis, and hyperplasia. The superficial dermis contained moderate edema, hemorrhage, and pigmentary incontinence, and was infiltrated by granulocytes and mononuclear cells. The laminated crusts contained numerous branching filaments of gram-positive coccoid bodies arranged in parallel rows, consistent with cutaneous Dermatophilus congolensis infection. This diagnosis was confirmed through bacterial culture and 16S rRNA PCR analysis. In the presented case, factors that might have contributed to disease progression include climatic conditions at the capture site and stress associated with trapping and laboratory housing.