A hypothesis for explaining the geographical distribution of Crohn's disease

The etiology of Crohn's disease (CD) remains unknown, although there is epidemiological evidence supporting an environmental influence. Recent molecular techniques, including polymerase chain reaction, have renewed interest in a possible etiological role of Mycobacterium paratuberculosis, which has been isolated from a number of CD patients. The organism causes a chronic enteritis in animals called paratuberculosis, a condition with many clinical and pathological similarities to CD. This review compares the epidemiology of paratuberculosis in animals with the epidemiology of CD in humans. There is considerable overlap of regions with high prevalences of paratuberculosis and CD. This finding adds support to the implication of M paratuberculosis in the etiology of CD.