The Role of Infection in Inflammatory Bowel Disease: Initiation, Exacerbation and Protection

Inflammatory bowel diseases are disorders involving the chronic inflammation of the gastrointestinal tract marked by episodes of exacerbations interspersed with remissions in genetically susceptible individuals. Over the past several years, advances have been made in understanding the pathomechanisms underlying these diseases. The realisation that both exogenous pathogens and pathogens endogenous to the host's microbiota are a fundamental part of the disease stimulation, progression and exacerbation has crystallized. Mycobacterium paratuberculosis, Listeria monocytogenes and Clostridium difficile, as well as viruses such as measles, mumps, rubella, Epstein-Barr virus and cytomegalovirus, have been implicated in disease causation and propagation. Conversely, helminthes and Helicobacter pylori are being investigated in relation to their potentially protective or beneficial effects on disease progression, and they are increasingly becoming a part of the biological treatment options used today. In this review we present the contrasting roles of various pathogens, providing evidence of their importance and contribution to the spectrum of IBD.