Amoebiasis

Key facts

• Amoebiasis is an infection of the large intestine caused by Entamoeba histolytica, a single-celled parasite spread through contaminated food and water.
• Most people who pick up the parasite have no symptoms. When illness does develop, it typically causes diarrhea, often with blood or mucus, plus cramping and urgency.
• In a small number of cases, the parasite spreads beyond the gut, most often to the liver, causing an abscess with fever and pain on the right side of the abdomen.
• Treatment is a full course of an antiparasitic medicine such as ornidazole; stopping early can leave cysts behind and let the infection return.

What amoebiasis is

Entamoeba histolytica colonizes the large intestine after being swallowed in contaminated food or water. Many carriers never notice it: the organism can live in the gut for months without causing illness. When it does turn invasive, it damages the intestinal lining and can trigger anything from mild loose stools to severe dysentery.

Symptoms

Symptomatic amoebiasis usually starts with diarrhea, sometimes containing blood or mucus, along with abdominal cramping and a persistent urge to pass stool. Symptoms can take days to weeks to appear after exposure. Rarely, the parasite migrates through the bloodstream to the liver, producing an amoebic abscess: fever, right-sided abdominal pain, and a general feeling of being unwell. This form needs prompt medical attention.

How amoebiasis is treated

Intestinal amoebiasis responds well to nitroimidazole antiparasitic drugs. Ornidazole is one option; it works by disrupting the parasite's DNA and clearing the infection from the gut. Completing the full course matters even if symptoms ease within a day or two, since an incomplete course can leave cysts that let the infection recur or spread to others through continued shedding.

When to see a doctor

Get medical assessment if diarrhea is severe or bloody, if fever runs high, or if symptoms don't improve within a few days of starting treatment. Seek urgent care for fever combined with right-sided abdominal pain, which can signal a liver abscess.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.