Mast-cell rich perivascular dermatitis accompanying the ulcerative lesions resulting from infection of Staphylococcus aureus in C57BL/6 mice

Introduction C57BL/6 mice and strains on the C57BL/6 mice are uniquely susceptible to ulcerative dermatitis. Ulcerations are seen in the dorsal scapulae, torso, shoulder and facial sites. These lesions are accompanied by severe pruritis-induced self-trauma, progressing from super facial excoriations to deep ulcerations (Sundburg et al 1994; Kastenmayer et al 2006). Though the etiology of this ulcerative dermatitis is not clarified, investigators proposed multifactorial etiology such as immune-complex vaculitis (Sundburg et al 1994), primary follicular dystrophy (Sundberg et al 2011), strain-related behavioral manifestation (Garner et al 2004; Williams et al 2012) and development hairinduced oronasal inflammation (Duarte-Vogel et al 2011). Health monitoring of SPF and conventional animals (mice and rats) was performed in our laboratory center. During this health monitoring program, it was occasionally encountered severe ulcerative dermatitis in C57BL/6 strain mice. It was found that the development of the unique skin lesions was closely associated with the opportunistic infection with Staphylococcus aureus (S. aureus). The purpose of this study was to investigate the health status of mice and rats in our laboratory animal facilities [specific pathogen free (SPF) and conventional facilities]. The incidence of S. aureus was compared between SPF and conventional rodents. In addition, severe ulcerative dermatitis in C57BL/6 strain mice was investigated for their macroscopic and microscopic changes.