Entamoeba histolytica (PCR)

The most important disease-causing amoeba in the human gut. Can cause invasive amoebiasis (amoebic dysentery) and liver abscess. PCR distinguishes it from harmless E. dispar.

How Entamoeba histolytica lives

Entamoeba histolytica is taken up as a cyst through contaminated water or food. In the small intestine the motile trophozoites hatch from it, migrate to the large intestine and feed there on bacteria. In most infected people that is where it stays: the amoebae live inside the gut without attacking the lining and are excreted as new cysts, which remain infectious outside the body for weeks. Under the microscope, E. histolytica, the harmless E. dispar and E. moshkovskii look the same; only detection of their genetic material tells them apart.

How Entamoeba histolytica attacks the gut lining

When the amoeba becomes invasive, it attaches to mucus and gut cells with a sugar-binding protein (Gal/GalNAc lectin). Cysteine proteases break down the protective mucus layer, antibodies and the connective tissue between the cells. Pore-forming proteins, the amoebapores, punch holes in the membranes of the gut cells, and the amoeba bites off pieces of living cells until they die. This is how flask-shaped ulcers form in the wall of the large intestine. Neutrophil granulocytes that are attracted are also killed and in the process release enzymes that enlarge the tissue damage – which explains the bloody, mucous diarrhoea and abdominal pain.

What happens when Entamoeba histolytica invades tissue?

From the ulcers, amoebae can enter the portal vein, which carries blood from the gut to the liver. In the liver they dissolve tissue and an abscess forms, with fever and pain in the right upper abdomen – sometimes only months after a stay in an area where the pathogen is widespread, and even without preceding diarrhoea. The lungs or brain are affected more rarely. In studies, invasive courses occurred more often in men, with malnutrition, during cortisone treatment and in pregnancy. E. histolytica is not part of the normal gut flora; if its genetic material is not found, it is absent from the sample.

The interpretation is given in your report.