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American Academy of Microbiology Colloquium, June 2006; Publication June 2007
Question the Colloquium addressed is whether MAP has evolved to infect human gastrointestinal tissue and whether once there it can cause disease.
28 participants met for 3 days to discuss and debate a number of questions surrounding MAP and human disease
Participants included microbiologists, human geneticists, immunologists, molecular biologists, food microbiologists, diagnostics developers, veterinarians, public health officials, gastroenterologists and patients.
Facts that DID NOT support existence of a link between MAP and CD:
Dairy farmers and others who may have greater exposure to MAP than the general population did not experience higher rates of CD in one study
There are some dissimilarities in the clinical and pathological presentation of CD and Johne’s disease
Cell-mediated immune responses to MAP or MAP antigens have not been demonstrated in CD patients.
No systematic studies, but CD has not been reported to worsen with progressive immunocompromise, such as happens with M. tuberculosis infections (exacerbated by HIV or anti-TNF α therapy)
In a controlled clinical trial, CD patients undergoing 6 months of antibiotic therapy did not maintain a sustained response to the drugs and the relapse rate after 2 years was similar in treated and control groups.
Blood samples from 58 subjects were blindly coded and investigated by three independent laboratories for the presence of Mycobacterium avium subspecies paratuberculosis (MAP) using MGITpara specialized media and nested PCR. Consequently, viable MAP was detected in 22/40 (55%) IBD (11/20 CD and 11/20 UC) compared to 4/18 (22%) NIBD (P<0.009). At least two centers detected MAP in 41% IBD samples compared to none (0%) in NIBD (P<0.0001). No sample was positive by all three centers. Despite result variability between centers, the study strongly demonstrates that using MGITpara culture media and nested PCR are essential for successful detection of MAP in human blood. Overall, the study supports a mycobacterial role in CD pathogenesis.
MAP in early onset CD 140 patients: 2 – 16 yrs age Prospective samples no medication Optimised DNA extraction Controlled, MAP specific PCR Long term culture for MAP (Kirkwood; Inflamm. Bowel Dis.2009) Bull, (2009) 0% 8% 16% PBMC PCR 0% 32% UC 0% 15% Non-IBD 40% 39% CD Biopsy Culture Biopsy PCR
Paratuberculosis and Crohn's Disease: Already beyond reasonable doubt Tim Bull
“ For MAP not to contribute to pathogenesis and merely to have a bystander role, it would be necessary to accept that despite its specific ability to cause chronic inflammation of the intestine in so many animals, including primates, it is somehow harmless to man.”
(Herman –Taylor et al., J. Med Microbiol, 2002)
“ The critical issue today is not whether MAP is associated with CD, but whether MAP causes CD or is only incidentally present, not an inciter or participant in the disease process.”
(Nacy et al. American Society for Microbiology 2008)
MAP Transmission regularly occurs from animals to humans
Can MAP actively invade and persist in human gut epithelium? Bull, (2009)
MAP Infection into human gut is an active process
Human foetal ileum xenographed to SCID mice
(Golan: J. Inf. Dis. 2009)
MAP M. smegmatis 3/9 donors 6/9 donors 9/9 donors Active Invasion Low Invasion Low Invasion Severe Inflammation Mild Inflammation No damage Epithelial damage No damage Bull, (2009)
MAP and HD5 HD5 expression is significantly reduced in the gut of CD patients. HD5 inhibits entry of MAP into human macrophage cell lines NOD2 mutation leads to HD5 depletion leads to MAP infection? Bull, (2009)
MAP Detection “ The association of MAP and Crohn’s disease, based on PCR or ELISA testing is well established” MAP +ve are 7 fold more likely in CD than Normals 10 – 40% presence of MAP in Non-STERILE and STERILE samples from Normals MAP is chronically and actively invading humans Bull, (2009)
MAP culture and VNC phenotype Viable Non-Culturable (lag) phase increases with repeated cycles of heat shock. Bull, (2009)
MAP culture and VNC phenotype MAP infection into human macrophages leads to Viable Non-Culturable (VNC) phenotype. Bull, (2009)
MAP culture and VNC phenotype MAP becomes Viable Non-Culturable (VNC) on intracellular entry Some Crohn’s Disease therapies are inhibitory to culture Immunotherapy (which aggravates MTB infection) does not promote MAP growth Negative MAP culture is NOT necessarily indicative of Negative MAP infection CD patients on some long term therapies may not be suitable for MAP culture studies Bull, (2009)
Summary MAP can and does Infect and persist in Crohn’s patients Respond to anti-MAP therapeutics in Crohn’s patients Exploit CD susceptibility gene defects to promote chronic persistence Generate a Th17 biased immune dysregulation that COULD lead to Crohn’s Disease Bull, (2009)
Verdict Viable chronic MAP infection is present in most patients with Crohn’s Disease MAP infection can cause the immune dysregulation that is the major predisposing factor to the development of Crohn’s Disease Bull, (2009)