Amoebiasis (amoebic dysentery): symptoms, diagnosis and treatment

Amoebiasis is an infection of the gut caused by a single-celled parasite, Entamoeba histolytica. Patient UK's professional reference explains that humans are the only reservoir, and that infection occurs by swallowing mature cysts in food or water, or on hands contaminated by faeces. The cysts release active parasites in the small intestine, which can invade the lining of the large intestine and cause ulcers.

From the bowel the infection can spread to other organs, most often the liver, and less often the lungs and brain. Asymptomatic carriers pass cysts in faeces, which is how the infection spreads, and the same source notes that cysts remain viable for up to two months.

The term amoebic dysentery is used when infection causes bloody diarrhoea. Most amoebiasis in the UK is imported by people who have travelled to or lived in areas with poor sanitation, although it can also spread within households and between sexual partners.

Patient UK says that most cases occur in developing countries where poor sanitation allows contamination of drinking water and food with faeces. In industrialised countries, risk groups include immunocompromised people and people in institutions. Travellers and immigrants are also at risk, and increased prevalence has been seen in men who have sex with men who engage in oral-anal sex.

Because the infection can persist silently, a person may be found to have it long after travel. Symptoms can also appear months after exposure.

About 90% of infections are asymptomatic. When symptoms occur, Patient UK says they begin with lower abdominal pain and diarrhoea and may progress to dysentery with blood and mucus in the stool. The incubation period may be as short as seven days, and tissue invasion mostly occurs during the first four months.

The NHS advises that diarrhoea and vomiting can usually be treated at home with plenty of fluids, but to call NHS 111 for bloody diarrhoea or bleeding from the bottom, diarrhoea for more than 7 days, vomiting for more than 2 days, or signs of dehydration, and to call 999 or go to A&E for vomiting blood, severe tummy ache or confusion.

If you have had diarrhoea after travelling abroad, especially with blood in the stool, fever or persistent symptoms, tell your GP about your travel history so that stool tests for parasites can be arranged. A fever with right-sided upper abdominal pain after travel needs prompt assessment because of the possibility of liver abscess.

Patient UK lists blood tests, stool examination and, for suspected invasive disease, serology and imaging. It notes that microscopy has low specificity, that E. histolytica must be distinguished from the non-pathogenic but identical-looking E. dispar, and that the World Health Organization now recommends specific stool testing such as cultures, antigen testing or PCR.

Antibody tests are positive in nearly 100% of cases of liver abscess and in most invasive bowel disease, according to the same source, and ultrasound, CT or MRI of the abdomen can show liver abscesses. Endoscopy with biopsy may be used in some cases. It adds that barium studies are contraindicated in acute amoebic colitis because of the risk of perforation.

Patient UK says that fluid and electrolyte replacement may be required, that metronidazole is the first choice for acute invasive amoebic dysentery, and that tinidazole is also effective. Treatment with either is followed by a 10-day course of diloxanide furoate to destroy any amoebae remaining in the gut.

For amoebic liver abscess, metronidazole and tinidazole are effective, with diloxanide furoate again given afterwards to clear the gut. It notes that abscesses resolve slowly and may increase in size during treatment, so clinical response, rather than repeated scans, is more important in monitoring progress. Diloxanide furoate is the drug of choice for asymptomatic people passing cysts.

Treatment should be directed by a clinician, ideally with infectious diseases advice.

UKHSA publishes interim public health operational guidelines for amoebiasis to support public health practitioners, environmental health officers and healthcare professionals to manage cases of E. histolytica infection, together with a template GP letter and patient information leaflet for confirmed cases.

The NHS advises on diarrhoea more generally to wash hands with soap and water frequently, to stay off school or work until you have not been sick or had diarrhoea for at least 2 days, to clean toilet seats, flush handles and taps daily, not to prepare food for others and not to use a swimming pool until at least 48 hours after symptoms stop.

On the NHS, a GP can arrange stool tests, and UKHSA's guidelines are intended for public health practitioners, environmental health officers and healthcare professionals managing confirmed cases.

Private travel clinics and GPs can arrange stool testing and consultation, often faster. Because specific tests such as PCR are needed to separate E. histolytica from harmless look-alikes, ask which test is being used, and share results with your NHS GP.