The infection is caused by a parasite called "Entamoeba histolytica." (EH)

These are microscopic one-celled parasites commonly known as amoebas. Entamoeba histolytica exists as two forms in contaminated food and drink

As free amoebae (known as "trophozoites")

As infective cysts, which are a group of amoebae surrounded by a protective wall, which have been passed in the faeces of the carrier (human or animal).

As these parasites live in the large intestine, they travel in the feces of infected people, and can contaminate water supplies in places where sanitation is poor.

The parasite spreads by

The contamination of fruits and vegetables grown in areas where human feces are used as fertilizer.

Dirty hands of infected people especially after bowel movement when they don't wash their hands properly.

Once amoebas enter the mouth, they travel through the digestive system and settle in the large intestine. A harmless strain of the parasite (Entamoeba dispar) can live in the intestine without causing damage.

E. Histolytica can also sometimes live in the intestine without causing symptoms, but it can cause severe disease-

These amoebas may invade the wall of the intestine and can cause small ulcers and inflammations leading to amoebic dysentery.

These amoebas also may pass into the bloodstream and sometimes travel to the liver and rarely, to the brain, where they can form pockets of infection leading to abscesses.