• irritable bowel syndrome
• diarrhoeal disease
• infectious diarrhoea
• mast cells

Human intestinal spirochetosis (HIS) has been recognised since the early days of histopathology but similar to Helicobacter pylori, its presence is inconsistently linked to disease so it is usually dismissed as a harmless commensal.1 The condition is caused by Brachyspira, a genus of anaerobic bacteria whose spiral form and periplasmic flagellae allows them to easily glide through colonic mucus which is their normally habitat. They were first reported in 1719 when Van Leeuwenhoekreported moving spiral ‘animalcules’ in his own stools. HIS can be identified from a blurry red fringe on the intercryptal epithelial surface seen throughout the colon in sections stained with H&E. Electron microscopy shows myriads of organisms lined up perpendicular to the mucosa, the proximal tip embedded in but not penetrating an invagination of the host cell membrane (figure 1). Conventional histology finds HIS in 0.4% in a hospital series in Japan and 2.3% in a population survey in Sweden2 but 39% in male homosexuals in the UK with a link to or0-anal contact but not HIV status.3 Many cases of HIS appear to be asymptomatic, one large Australian survey of 113 cases of HIS found only 10 cases with obvious inflammation, 6 of whom had other explanations for the inflammatory response.4 Detailed morphological examination in isolated case reports suggests that GI symptoms only occur when spirochetes invade beyond the …