Naser SA et al. (2004) Culture of Mycobacterium avium subspecies paratuberculosis from the blood of patients with Crohn's disease. Lancet 364: 1039–1044

Since Crohn's disease is clinically and histopathologically similar to tuberculosis, leprosy and paratuberculosis, it has been suggested that the disease is caused by a mycobacterial infection. Several studies have detected Mycobacterium avium subspecies paratuberculosis (MAP) in tissue samples and breast milk from patients with Crohn's disease. Results have been inconsistent, however, and the role of this organism in the etiology of the disease remains controversial. A recent study by Naser and colleagues has shown that viable MAP was detected more frequently in peripheral blood from Crohn's disease patients than in controls.

The study included 28 patients with Crohn's disease, 9 with ulcerative colitis and 15 individuals with no inflammatory bowel disease. Whole blood samples (4 ml) were taken from each participant and the buffy coat layer was used either for genomic DNA extraction for PCR analysis, or for culture.

A MAP-specific DNA fragment was amplified by PCR from a higher proportion of the Crohn's disease samples (46%) and ulcerative colitis samples (44%) than in the controls (20%). Positive MAP cultures were obtained from 50% of the patients with Crohn's disease and 22% of those with ulcerative colitis, whereas all control cultures were negative for MAP.

The study provides more evidence that MAP may be involved in the etiology of Crohn's disease, and Naser et al. recommend that larger studies be performed to investigate this further.