Hi, Old Mike, sorry for the delay. I am in a vacation with my family with busy schedules and limited access to Internet. It had been a pleasure to have exchanged thoughts, ideas and information over the email, and thanks for your interest in my opinion on the possible link between Mycobacterium avium subsp. paratuberculosis (MAP) and IBD, especially Crohn’s disease (CD).
Not like saccharin and sucralose, MAP as the possible cause of Crohn’s disease had been suspected for about a century, with extensive studies by some researchers, especially in the last several decades. Despite that, the results remains highly controversial, largely because the conflicting “facts” in almost every aspects. To my knowledge, there is also a big discrepancy between the incidence of IBD and contamination of MAP in some countries. For instance, Sweden had been one of the countries with the highest incidence of IBD, including both CD and ulcerative colitis (UC), but MAP contamination had been extremely low (see Sternberg Lewerin S et al. Control of paratuberculosis in Sweden. Proceedings of the 9th International Colloquium on Paratuberculosis 2007, p. 319-323.
http://www.paratuberculosis.info/web...ories/pdfs/274). Back to 1952, MAP had been included in the Swedish Epizootic Act (SFS 1999:657). According to this legislation any suspicion of MAP is notifiable for animal owners, veterinarians or other professionals with animal contact, regardless of the species of the animal. Moreover, it required the Swedish Board of Agriculture must investigate all suspect cases and take all necessary means to eradicate and prevent the spread of the infection, if confirmed. As the result, although there were a few sporadic cases of MAP infection in cattle since 1993, all the cases were directly or indirectly linked to the imported animals, with all cases being beef herds, but none in dairy herds. The negative finding of domestically originated MAP in the more than 1.5 million of cattle and about half a million of sheep all over the country suggested the extremely low, if not zero, MAP contamination in Sweden, despite the very high incidence of CD and UC seen in many cities in Sweden like Stockholm, Uppsala, Orebro, Malmo, and Gothenburg.
In addition, there were also many conflict results regarding other aspects on the suspected link between MAP and IBD. Although some studies (like the one in Forest Virginia) suspected that contamination of MAP in the pasteurized milk or the water supply may cause CD in human, other studies failed to show any increased risk for dairy farmers with a more direct and certain contact with MAP through the infected animals (Jones PH, et al. Crohn's disease in people exposed to clinical cases of bovine paratuberculosis. Epidemiol Infect 2006;134:49-56). Although study indeed found MAP in the lymph nodes of feral cats on the contaminated farm, they did not had the signs of IBD (Palmer MV et al. Isolation of Mycobacterium avium subsp paratuberculosis (Map) from feral cats on a dairy farm with Map-infected cattle. J Wildl 2005;41:629-35).
At beginning people were suspected a similar origin for both Johne’s disease in cattle and CD in humans as they both showed the obstructive damage near the end of the ileum. However, as shown in some of the recent studies, there was a shift of CD from the small intestine to large intestine over time and the involvement of only large intestine has become the main form for CD (the Crohn’s colitis). I suspected that IBD now would be more mimic the commonly seen IBD in pet dogs and cats rather than the Johne’s disease in cattle (Qin X. What is human inflammatory bowel disease (IBD) more like: Johne's disease in cattle or IBD in dogs and cats? Inflamm Bowel Dis. 2008 Jan;14(1):138). There were also many other fundamental differences between Johne’s disease and CD. For instance, large amounts of MAP can be found in the mucosa or feces of cattle with Johne’s disease, which can be transmitted to healthy herds; in contrast, the bacteria are hardly seen in the tissues and feces of patients with CD, and IBD in general is regarded as noncontiguous. Although studies showed higher rates of existence of MAP in gut tissue of CD patients by the high sensitive methods such as the PCR detection of the IS900 DNA segments, there are also increase in other bacteria such as Helicobacter spp., Listeria monocytogenes and Escherichia coli, suggesting this could be just reflected the weakening of gut barrier and increased gut permeability (Tiveljung A, et al. Presence of eubacteria in biopsies from Crohn's disease inflammatory lesions as determined by 16S rRNA gene-based PCR. J Med Microbiol 1999;48:263-8). Finding of viable MAP in patients with CD would be important evidence for the possible link. However, the more rigorous test organized by NIH failed to repeat and confirm these findings (Van Kruiningen HJ. Where are the weapons of mass destruction - the Mycobacterium paratuberculosis in Crohn's disease? J Crohns Colitis 2011;5:638-44). Therefore, it would be no surprising that there are many deep believers on both sides. Both sides think they hold enough scientific evidences. However, one thing would be true: one side must be wrong, along with the many “solid scientific facts”.