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For decades, Mycobacterium avium subspecies paratuberculosis (MAP) has been linked to the pathogenesis of Crohn's disease. Despite many investigations and research efforts, there remains no clear unifying explanation of its pathogenicity to humans. Proponents argue Crohn's disease shares many identical features with a granulomatous infection in ruminants termed Johne's disease and similarities with ileo-cecal tuberculosis. Both are caused by species within the Mycobacterium genus. Sceptics assert that since MAP is found in individuals diagnosed with Crohn's disease as well as in healthy population controls, any association with CD is coincidental. This view is supported by the uncertain response of patients to antimicrobial therapy. This report aims to address the controversial aspects of this proposition with information and knowledge gathered from several disciplines, including microbiology and veterinary medicine. The authors hope that this discussion will stimulate further research aimed at confirming or refuting the contribution of MAP to the pathogenesis of Crohn's disease and ultimately lead to advanced targeted clinical therapies.

Mycobacterium avium subspecies paratuberculosis (MAP) is suspected to be a causative agent in Crohn's disease. Recent evidence suggests that MAP can induce the expression of Matrix Metalloproteinases (MMPs), which are the main proteases in the pathogenesis of mucosal ulcerations in inflammatory bowel disease (IBD). Within the present study, we analysed whether oral MAP exposure can induce colonic MMP expression in vivo. In MAP exposed mice MAP and spheroplasts were visualized in intramucosal leukocyte aggregates. MAP exposed mice exhibited a higher colonic expression of Mmp-2, -9, -13, -14, Timp-1, Tlr2, Tlr6, Il-1β, and Tnf-α. Cell clusters of MMP-9 positive cells adjacent to intramucosal leukocyte aggregates and CD45(+) leukocytes were identified as the major cellular sources of MMP-9. Enhanced TLR2 expression was visualized on the luminal side of colonic enterocytes. Although MAP exposure did not lead to macroscopic intestinal inflammation, the observed MAP spheroplasts in intramucosal leukocyte aggregates together with increased colonic expression of toll-like receptors, pro-inflammatory cytokines, and MMPs upon MAP exposure represents a part of the host immune response towards MAP., (Copyright © 2012 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

Based on more than 30 literature references, the author tries to explain the phenomena of paratuberculosis in cattle. He gives a short description of the origin of the infection, the disease categories, the diagnostic problems and eradication. Also the human infection with the Mycobacterium known as Mycobacterium avium supspecies paratuberculosis (MAP)--a recognized pathogen in animals causing some or possibly all cases of Crohn's disease will be discussed. The conclusion is that until now no study gives evidence that MAP may be transmitted to humans through foods derived from cattle with MAP infection.

Although Crohn's disease is considered to be autoimmune in origin, there is increasing evidence that it may have an infectious cause. The most plausible candidate is Mycobacterium avium subspecies paratuberculosis (MAP). Intriguingly, Koch's postulates may have been fulfilled for MAP and Crohn's disease, even though they still have not been met for Mycobacterium leprae and leprosy. In animals MAP causes Johne's disease, a chronic wasting intestinal diarrhoeal disease evocative of Crohn's disease. Johne's disease occurs in wild and domesticated animals, including dairy herds. Viable MAP is found in human and cow milk, and is not reliably killed by standard pasteurisation. MAP is ubiquitous in the environment including in potable water. Since cell-wall-deficient MAP usually cannot be identified by Ziehl-Neelsen staining, identification of MAP in human beings requires culture or detection of MAP DNA or RNA. If infectious in origin, Crohn's disease should be curable with appropriate antibiotics. Many studies that argue against a causative role for MAP in Crohn's disease have used antibiotics that are inactive against MAP. However, trials that include macrolide antibiotics indicate that a cure for Crohn's disease is possible. The necessary length of therapy remains to be determined. Mycobacterial diseases have protean clinical manifestations, as does Crohn's disease. The necessity of stratifying Crohn's disease into two clinical manifestations (perforating and non-perforating) when interpreting the results of antibiotic therapy is discussed. Rational studies to evaluate appropriate therapies to cure Crohn's disease are proposed.

Mycobacterium paratuberculosis is the causative agent of Johne's disease, a chronic enteritis in ruminants. It has been suggested that Crohn's disease, a gastrointestinal disease in humans with similar clinical symptoms and histopathological findings, is caused by the same bacteria. Epidemiological data support Crohn's disease possibly being caused by an infectious agent. Recently, with improved culture techniques and the advent of polymerase chain reaction, M. paratuberculosis has been identified from tissues of increasing numbers of patients with Crohn's disease. However, conflicting data still occur and the case for M. paratuberculosis as the etiological agent of Crohn's disease can be neither proved nor disproved. The development of new diagnostic tests and comprehensive well-defined clinical studies will hopefully provide us with information about this association in the future.