Cutaneous Dermatophilosis in a Meadow Jumping Mouse (Zapus hudsonius)

Abstract

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.

Figure 1.

Meadow jumping mouse (Zapus hudsonius), external lesions. (A) White flakes, thick crusts, and scabbing on nonhaired skin of the feet and tail. (B) Small, round, pale-tan papules (diameter, <1 mm) on the face (white arrows). (C) Severe edema of the distal hindlimbs. Hematomas on multiple digits (black arrows). Papules similar to those on the face were present on the hindlimbs (red arrow) and forelimbs (not pictured).

Figure 2.

Meadow jumping mouse (Zapus hudsonius), affected skin. (A) Multilaminated crusts, resulting from extensive orthokeratotic and parakeratotic hyperkeratosis and intracorneal pustules (white arrows), expand the dermal architecture. Hematoxylin and eosin stain; magnification, 40×. (B) Hyperplasia characterized by prominent branching rete ridges, and frequent mitotic figures in the stratum basale (black arrows). Hematoxylin and eosin stain; magnification, 200×. (C) Intracorneal pustules characterized by low to moderate numbers of granulocytes. Hematoxylin and eosin stain; magnification, 400×. (D) The epidermal surface contained crusts composed of cellular debris and degenerate granulocytes admixed with numerous long branching filaments of coccoid organisms. Hematoxylin and eosin stain; magnification, 600×. Insert: affected epidermal surface; Modified Gram stain; magnification, 600×.

Figure 3.

Dermatophilus congolensis, morphologic characteristics of bacterial colonies cultivated from affected skin. (A) Colonies were gray to white, raised, irregularly shaped, and β-hemolytic, with a rough surface. (B) Organisms were gram-positive with coccoid morphology and formed large aggregates of branching filaments. Gram stain; scale bar, 10 μm.