PURPOSE OF REVIEW: Though long hypothesized, the putative link between Mycobacterium avium paratuberculosis and Crohn's disease remains neither confirmed nor refuted. This article reviews published contributions that directly or indirectly address this question. RECENT FINDINGS: Epidemiologic studies, looking for M. avium paratuberculosis DNA in Crohn's tissue, show a strong association between the agent and this disease. Supporting data, however, are presently inconclusive on a causal role. Genetic studies provide indirect support for a role of mycobacteria in Crohn's disease, by identifying susceptibility genes that encode proteins implicated in innate immunity to intracellular bacteria. Clinical trial data support at least a short-term benefit for antimycobacterial therapy in Crohn's disease, but the microbial specificity of this response is presently unknown. SUMMARY: There appears to be a strong association between M. avium paratuberculosis and Crohn's disease, but the causality of this association is unknown. Consequently, the therapeutic implications of this association require further study. A number of critical questions about the biology of M. avium paratuberculosis remain unanswered. Data from studies of this organism, and its interaction with the immune system, can help address proposed reasons for or against a role of M. avium paratuberculosis in the etiology of Crohn's disease.
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