Dermatitis and Corynebacterium bovis infection in athymic nude rats (Rattus norvegicus)

Corynebacterium bovis (Cb) is a bacterium that causes a flaking dermatitis characterized histologically by orthokeratosis, acanthosis, intracorneal bacterial colonies and variable dermal inflammation in immunodeficient mice. Although Cb has been shown to establish dermal colonization in rats, its impact on the skin of immunodeficient rats remains poorly defined. This case series characterizes cutaneous lesions in 22 naïve or experimentally manipulated NIH-Fox1^rnu (nude) rats and evaluates the association between Cb infection and dermatitis over a 5-year period. Histologically, all rats had orthokeratosis and dermatitis/folliculitis, 21/22 had acanthosis, 15/22 had bacterial presence and 9/22 had transepidermal/transfollicular keratinocyte apoptosis. Additional variable findings included furunculosis, pustules, dermal oedema and perivascular dermatitis. Inflammatory infiltrates consisted of CD3-positive lymphocytes and Iba1-positive macrophages located predominantly at the dermoepidermal junction. Corynebacterium bovis was isolated from the skin of 15/22 affected rats, and in-situ hybridization confirmed intracorneal/intrafollicular colonies of Cb in 3/11 rats examined. Nude rats also developed cutaneous lesions that corresponded histologically with a lymphocytic dermatitis, the distribution of which was often independent of Cb colonies. This study documents the first spontaneous Cb infection with dermatitis in nude rats. The frequent isolation of Cb from the skin raises the question of whether alterations in the cutaneous microbiome of nude rats may contribute to the immune modulation of dermatitis, warranting further investigation.