Diagnostic histopathology of infections of the luminal gastro-intestinal tract: ‘small blue dots’, worms and sexually transmitted infections of the distal gastro-intestinal tract

Infectious diseases of the luminal gastro-intestinal (GI) tract are a major cause of morbidity and mortality worldwide. Most are not biopsied, and when they are, do not produce specific microscopic appearances. This review focuses on infectious agents of the luminal GI tract which are likely to find their way to the desk of the UK histopathologist, and present diagnostic difficulties. For that reason, relatively common infections, such as candidal and herpes viral oesophagitis, giardiasis and cytomegalovirus infection are omitted. This review instead concentrates on the less well recognized protozoal and helminthic infections and their differential diagnoses. Also discussed is an area of rising importance in the UK, sexually transmitted infections of the distal GI tract; as the histological appearances may be non-specific, a high index of suspicion is required, and the histopathologist may have the opportunity to be the first to suggest the diagnosis.