Histologic characteristics of human intestinal spirochetosis in operatively resected specimens

Human intestinal spirochetosis (HIS), one of the zoonoses, is caused by colonization by Brachyspira species bacteria within the large intestine. Histologic diagnosis of HIS is usually established by finding “fringes” on the colonic surface epithelium in biopsy specimens. However, its histologic characteristics, especially beneath the colonic mucosa, have not been elucidated. The present study was designed to examine the histologic characteristics of HIS in operatively resected specimens. We reviewed operatively resected (colectomy or appendectomy) specimens obtained in six consecutive years at a single medical center. HIS was diagnosed histologically by finding “fringes”. Immunohistochemical study using anti-Treponema pallidum antibody, which cross-reacts with Brachyspira, was additionally performed. A total of 848 (M:F = 477:371; median age, 59 years; 12–94 years) colectomy and/or appendectomy cases were examined, and the seven cases (0.8%) diagnosed as having HIS were all male (1.5% of male cases). Four HIS cases (0.8% of 508 colectomy cases (1.4% of 285 male-cases)) were colectomy cases with cancers, and the other three (0.9% of 340 appendectomy cases (1.6% of 192 male-cases)) were appendectomy cases for acute appendicitis. Our study revealed (1) a heterogeneous distribution of diagnostically important “fringes” within the large intestine, (2) an ileal presence of Brachyspira, (3) superficial location of HIS-related findings among anatomical wall layers, and (4) the presence of Brachyspira or its derivatives within macrophages in the lamina propria and immune apparatus (lymphoid follicles in superficial wall structures (lamina propria or submucosa) and lymph nodes). Investigation using operatively resected specimens might help elucidate the characteristics of HIS. Brachyspira may have immunogenicity in humans.