A study in this week’s issue of THE LANCET suggests that Crohn’s disease may be caused by Mycobacterium avium subspecies paratuberculosis (MAP), the same bacterium that causes a similar intestinal disorder (known as Paratuberculosis or Johne’s disease) in cattle, sheep, and goats.
Crohn’s disease, a form of inflammatory bowel disease (IBD) with at least one million diagnosed cases worldwide, resembles some aspects of tuberculosis, leprosy, and paratuberculosis. The role of MAP, first identified from a person with Crohn’s disease 20 years ago, remains controversial. Saleh A Naser (University of Central Florida, USA) and colleagues used microbiological and molecular biology techniques to investigate the presence of MAP in the blood of 28 individuals with Crohn’s disease, nine with ulcerative colitis, and 15 without inflammatory bowel disease.
The live bacterium (viable MAP) was cultured from the blood of 14 (50%) patients with Crohn’s disease, two (22%) with ulcerative colitis, and none of the people who did not have IBD.
Dr Naser comments: “This is the first study designed to culture MAP from human blood. We detected viable MAP in peripheral blood in half of patients with Crohn’s disease and none in those people who did not have IBD. The two ulcerative colitis patients with viable MAP may represent misdiagnosis or possible co-infection cases. Detection of Viable MAP in the blood of Crohn’s disease patients suggests that MAP infection in this IBD may be systemic. In addition to the fact that the outcome of our study contributes to the evidence that MAP might be a cause of Crohn’s disease, it is of great interest to address the epidemiologic source of MAP in these patients. A multi-centre, larger-scale investigation is urgently needed”.
In an accompanying commentary (p 1013), Warwick S Selby (Royal Prince Alfred Hospital/University of Sydney, Australia) concludes: “This report by Naser et al may still fall short of proving that MAP is one of the causes of Crohn's disease but as with similar studies it raises many important questions. The findings now need to be replicated in other laboratories. Whatever one’s view, MAP cannot continue to be ignored in Crohn's disease. Funding bodies, laboratory and clinical researchers must clarify with some urgency, once and for all, whether this organism is important in Crohn's disease or is merely a curious bystander. This is not just for the patients but also in the interest of public health”.