Clinical and Pathological Comparison of Paratuberculosis and Crohn's Disease

Crohn's disease is a chronic systemic inflamma­tory condition presenting primarily with gastro­intestinal pathology. It is a debilitating disease, which typically leads to weight loss, abdominal pain, diarrhoea and obstruction, among others (Chiodini, 1989).

‘Corresponding author: shannon.duffy@mail.mcgill.ca © CAB International 2020. Paratuberculosis: Organism, Disease, Control, 2nd Edition (eds M.A. Behr et al.)

FISH, fluorescence in situ hybridization; MAP, Mycobacterium avium subsp. paratuberculosis; PCR, polymerase chain reaction.

comparative pathology studies have emphasized that both disease tissues display relatively the same frequency of granulomatous enteritis, lymphoplasmacytic enteritis, oedema and lym- phangiesctasia (Zarei-Kordshouli et al., 2019).

However, differences have been observed between these two conditions. A comparative pathological study between 29 Crohn's disease, 17 ulcerative colitis and 35 bovine paratubercu­losis samples described Crohn's disease lesions as more destructive than paratuberculosis, as defined by the degree of damage to the epithe­lium, ulcer and fissure formation, among others (Momotani et al., 2012). Conversely, a recent study found that vasculitis was observed in near­ly all paratuberculosis tissues and only a small percentage of Crohn's disease tissues. The most prominent pathological difference between clas­sical paratuberculosis and Crohn's disease is the ability to readily visualize acid-fast bacteria in the diseased tissue from cattle (Zarei-Kordshouli et al., 2019). The detection of MAP in tissues of humans with Crohn's disease has proven incon­sistent or unsuccessful, a fact that will be dis­cussed in more detail in a future section.

Together, these observations demonstrate that the rationale implicating MAP in Crohn's disease is backed by the many similarities with paratuberculosis. However, it is noted that gran­ulomatous pathology is not pathognomonic for a single aetiology; other granulomatous conditions range from a wood splinter to beryl­liosis and include bacterial infections (e.g. lep­rosy) and fungal infections (e.g. histoplasmosis). Furthermore, while differences in pathologi­cal presentation between paratuberculosis and Crohn's disease might argue against a common aetiological agent, Crohn's disease is generally accepted to develop due to a combination of genetic, immune and environmental factors. Given the differences in genetics, immunology and environmental exposures between humans and cattle, the final clinical and pathological outcomes of a similar microbial exposure need not be identical.

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