Gastro-intestinal, Hepatic, Pancreatic, and Biliary Infections

The gastro-intestinal tract (GIT) hosts the most numerous and diverse reservoir of microbes in humans. There is increasing interest in the relationship between the GIT microbiome and human health. Obesity, diabetes, allergy, and a number of inflammatory diseases have been linked with the human GIT microbiome. Infections of the GIT arise either as a result of a change in the relationship between the commensal microbes colonizing the GIT (endogenous infection) or entry in to the GIT of a micro-organism which causes disease (exogenous infection). Commensals most commonly invade host tissues as a result of compromised defensive barriers. Disease associated with exogenous infection can be toxin-mediated, or associated with local or systemic invasion of the host. Endogenous infections are usually polymicrobial. In the mouth the aetiology, presentation, and anatomical associations have led to the description of a number of syndromes. Peritonsillar infection with involvement of the internal jugular vein is Lemierre’s syndrome, which is particularly associated with infection with Fusobacterium necrophorum. ‘Trench mouth’ is a severe form of ulcerative gingivitis, so named because in the absence of oral hygiene it was a relatively common diagnosis among those in the trenches during the First World War. Ludwig’s angina is a severe infection of the floor of the mouth which spreads in to the submandibular and sub-lingual space, often following a tooth-related infection. Deep neck infections are more common in children than adults and can involve the parapharyngeal, retropharyngeal, peri-tonsillar, or sub-mandibular spaces. Children with deep neck infections are more likely than adults to present with cough and respiratory distress. Oesophagitis has a wide range of potential aetiologies. Fungi (particularly Candida species) are probably the most common microbial cause of oesophagitis. Fungal infection of the distal oesophagus is thought to play an important role in the pathogenesis of disseminated fungal infection. Risk factors for fungal infection include poor oral intake, exposure to antibiotics, immunocompromise (HIV, steroids, cancer treatments), gastric acid suppressants, and damage to mucosal integrity (naso-gastric tubes, acid reflux, varices). Bacteria (including Mycobacteria, Actinomycetes, Treponemes), parasites, and viruses (herpes simplex, cytomegalovirus) are rarer infectious causes of oesophagitis.