Entamoeba Histolytica can cause a severe form of dysentery which can be lethal, particularly if it invades the lungs, liver or brain. It has a similar mode of transmission to Giardia and can also be caught from contaminated feces. What makes it so dangerous is that it can rapidly become invasive and pathogenic when the body becomes stressed from either physical or psychological problems.
There are a large number of species of amoeba which parasitize the human intestinal tract. Of these Entamoeba histolytica / dispar are the only species found to be associated with intestinal disease. Although many people harbor this organism world wide, only about 10% develop clinically invasive disease thus the parasite has been shown to present as two very differing clinical presentations. There is the commensal or non-invasive luminal form where the parasite causes no signs or symptoms of disease. There is also the pathogenic or invasive form where the parasite invades the intestinal mucosa and produces dysentery and may give rise to extra-intestinal lesions via the blood, mainly to the liver.
The invasive and non-invasive strains of E. histolytica can be differentiated by isoenzyme electrophoresis and the application of molecular biology has confirmed the presence of two distinct species with the same morphological features. The pathogenic or invasive species has retained the name E. histolytica and the non-pathogenic, non-invasive species has been named E. dispar.