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The case is unproved
Crohn's disease is an indolent chronic inflammatory disorder that may affect the entire alimentary tract, with inflammation through all layers of the intestine. Its pathogenesis is a mystery. Treatment remains non-specific and consists predominantly of immunosuppression.
The original description by Crohn suggested mycobacteria as a possible cause, given that chronic enteritis in animals, termed Johne's disease, was caused by tubercule bacilli. The many types of mycobacteria vary in their pathogenicity; some are saprophytic and rarely cause disease, while others are potentially pathogenic, particularly in immunocompromised patients. The pathogenicity of Mycobacteria paratuberculosis remains uncertain.
Research workers have tried for many years to culture mycobacteria from tissue affected by Crohn's disease, although generally without success. To unravel the complex mycobacteriology of chronic enteritis, investigators have developed sensitive methods to detect and characterise relevant pathogenic strains. Hermon-Taylor's group identified IS900, a DNA repetitive element, in an uncharacterised mycobacterial isolate from a patient with Crohn's disease. This was shown by DNA fingerprinting to be indistinguishable from M paratuberculosis, which causes enteritis in animals. The group suggests that assays based on polymerase chain amplification of highly specific DNA …