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Wednesday, January 07, 2009

One of the Causative organisms for Crohn's disease is Mycobacterium paratuberculosis

Question 82
One of the Causative organisms for Crohn's disease is
a.       Mycobacterium paratuberculosis
b.      Chlyamidia
c.       ??
d.      ??
a. Mycobacterium paratuberculosis
Harrison 16th Edition Page 1777
Crohn disease is an idiopathic, chronic inflammatory disorder of the bowel that involves any region of the alimentary tract from the mouth to the anus.
IBD may have an as yet undefined infectious etiology. Three specific agents have received the greatest attention, Mycobacterium paratuberculosis, Paramyxovirus, and Helicobacter species. The immune response to a specific organism could be expressed differently, depending upon the individual's genetic background. Although M. paratuberculosis had initially been identified in CD patients, further studies have not confirmed a disease association. In addition, antimycobacterial agents have not been effective in treating CD. A role for the measles virus or paramyxoviruses in the development of CD has been suggested based on an increase in the incidence of CD in England that paralleled use of the measles vaccine. However, studies in the United States have not substantiated this finding. In an animal model of IBD, Helicobacter hepaticus has been implicated as a trigger for the inflammatory response; evidence in people is lacking
Although there are many similarities between ulcerative colitis and Crohn disease, there are also major differences in the clinical course and distribution of the disease in the gastrointestinal tract. The inflammatory process tends to be eccentric and segmental, often with skip areas (i.e., normal regions of bowel between inflamed areas). Whereas inflammation in ulcerative colitis is limited to the mucosa (except in toxic megacolon), gastrointestinal involvement in Crohn disease is transmural. Among children with Crohn disease, the initial presentation most commonly involves ileum and colon (i.e., ileocolitis) but may involve the small bowel alone in about 40% (50% of children have terminal ileitis alone) or colon alone in about 10% (granulomatous colitis). Crohn disease may rarely present in the first years of life. As with ulcerative colitis, Crohn disease tends to have a bimodal age distribution with the first peak beginning in the late teens.
Several factors have been suggested in causation of crohns disease:
Ä     Genetic - in up to 20% of patients with Crohn's disease there is another family member affected by Crohn's or ulcerative colitis.
Ä     Low intake of fibre from fruit and vegetables has been associated with the development of Crohn's
Ä     Immune mechanisms - may be a down-regulating of the normal mucosal immune response in Crohn's


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