Entamoeba histolytica and Entamoeba dispar are distinct species; clinical, epidemiological and serological evidence.

The name of the causative organism of invasive amoebiasis, Entamoeba histolytica, was first introduced in 1903, even though this intestinal amoeba had been recognised since 1875. The marked disparity between the number of infected individuals and those with invasive amoebiasis resulted in a number of explanatory hypotheses being proposed. Although none of these were universally accepted, Brumpt's concept of two morphologically identical species gained increasing acceptance 50-60 years later when technology became available to investigate this anomaly. Sargeaunt spear-headed this drive by establishing the value of isoenzyme electrophoresis for studying the host-parasite relationship. From this foundation, incorporation of clinical, epidemiological and serological parameters to studies of the parasite resulted in the conclusion that a species complex comprising two morphologically identical amoebae was implicated with the disease. The two organisms have been named E. histolytica and Entamoeba dispar. The former is a pathogen and is responsible for invasive amoebiasis, while the latter is a gut commensal. Demonstration of the existence of this species complex has subsequently been confirmed by studies on the nucleic acids from several independent laboratories. The acceptance of E. histolytica and E. dispar as distinct species has had a major impact on our understanding of amoebiasis and its clinical management.