Protozoa and includes E. coli (that's E. coli, not E. coli. Get the difference?), E. dispar, E. moshkovskii, E. gingivalis, E. hartmanni, E. histolytica, E. hartmanni, E. polecki.
Eating the cysts aka fecal-oral. Blech. It can also be a sexually transmitted disease (PubMed).
E. histolytica: Asymptomatic cyst passage. 90% of human infections asymptomatic or mildly symptomatic. Bloody diarrhea and amoebic liver abscess which can rupture into the pleura, pericardium and peritoneum. Often those with diarrhea don't get liver abscesses and those with liver abscesses often have no diarrhea.
Get and O&P to diagnose diarrhea and serology for liver disease. The abscess, when drained looks, but does not taste, like chocolate milk. It is rare to see the amoeba in the stain.
Severe disease can mimic appendicitis, ischemic bowel disease, tuberculosis and malignancy (PubMed). Travel history can be so important. But sometimes the paratsite comes with the food and people get amebiasis with no good exposure.
E. coli and E. dispar are commensals and can be ignored, although
E. dispar and E. moshkovskii look exactly like E. histolytica and occasionally cause disease.
Large abscess in the liver may benefit from percutaneous drainage.
In Japan, HIV patients seropositive for E. histolytica had an increased risk of developing invasive disease (PubMed).