Entamoeba histolytica, commonly referred to as amoebas, is a protozoal parasite of the gut which is found in about 5-10% of the population, but around 20-30% of gay men. It is transmitted by oral-faecal contact when food or water supplies are contaminated, or during oral-anal sexual contact (rimming).

Symptoms and diagnosis

Symptoms can vary from none to very severe. Active infection causes bloody diarrhoea, wind, nausea and pain in the lower abdomen.

Infection can be diagnosed by examining a sample of stool (faeces) for the presence of the Entamoeba. These organisms can be present in the form of dormant cysts or active organisms known as trophozoites. A false negative result can be obtained if you are taking antibiotics, laxatives, antacids that contain castor oil or milk of magnesia, anti-diarrhoea medicines containing bismuth or kaolin (such as Pepto-Bismol), or you have had a barium meal or enema for X-ray purposes within the last fortnight. If symptoms continue even though the test is negative, it is worth having the test repeated.

Treatment

It usually responds well to standard anti-parasitic therapy with metronidazole (800mg three times a day for 10 days).