What is amoebiasis?
Amoebiasis is an infection of the gut caused by a parasite called Entamoeba histolytica, which is found in most tropical areas. Most people living in these areas have some form of parasite living within their intestine, but in many cases they are not caused any serious harm by it. Amoebiasis may be present in the local population, who will usually have no symptoms but can pass the parasite to others. Travellers to tropical countries are therefore at high risk of contracting some form of parasite which may cause serious illness.
What are the symptoms of amoebiasis?
Amoebae such as Entamoeba histolytica usually live in the large intestine. If they live on the surface of the intestine there will usually be no symptoms. However, if the parasite invades the wall of the large intestine and forms a cyst, this may cause ulceration and bleeding. Recurrent bouts of diarrhoea will also occur, with the appearance of blood and slimy mucous in the bowel motions. Dehydration may occur if insufficient fluid is taken to replace the fluid lost as a result of the diarrhoea. Unlike diarrhoea caused by bacteria, amoebic dysentery has a gradual onset and does not usually cause the high temperature (fever) associated with bacterial infections.
Amoebic liver abscesses can sometimes occur in people with amoebic dysentery but in most cases they will not be accompanied by any bowel symptoms. Cysts travel from the intestine to the liver in about one in five cases of amoebiasis, but abscess formation is uncommon. Abscesses cause severe pain over the liver and a high temperature. They can be dangerous and need urgent medical treatment.
Once a person is infected, amoebae will persist in the intestine for months or years and, although there may be no symptoms for a long time, it is still possible to develop illness many years later. The amoebae pass out of the body as cysts which can then infect another person. Carriers with no symptoms should be treated to prevent both future illness and the risk of infecting other people with the parasite.
What treatment is available?
Metronidazole (eg, Flagyl®), a type of antibiotic, may be given (as tablets or as syrup) for amoebic dysentery or liver abscess or for other forms of amoebic disease. It may also be given to eradicate the parasite in carriers with no symptoms.
Tinidazole (Fasigyn®) is another antibiotic which may be given for amoebic dysentery or amoebic liver disease as an alternative to metronidazole. Tinidazole is given as tablets.
If a person has no symptoms but a stool sample confirms the presence of amoebic cysts, medical treatment will be prescribed. A 10-day course of diloxanide tablets is given to eradicate the parasite in carriers with no symptoms. Diloxanide may be given alone for chronic (long-lasting) infections or after a course of treatment with metronidazole or tinidazole to destroy any amoebae in the intestine.
Chloroquine tablets (as Avloclor®) may be used to treat amoebic hepatitis.
Rehydration is very important. Electrolyte solutions can be taken to replace fluid and salts that are lost as a result of the diarrhoea. Rehydration preparations include Dioralyte®, Electrolade® and Rapolyte®. Plenty of clear liquids such as water or juice should also be drunk.
What can be done to prevent amoebiasis?
It is important to be careful about food in tropical countries where all forms of travellers' diarrhoea may occur.
- Avoid foods that may have been cooked some time before. Freshly boiled food, eg, rice and sweetcorn, is safe to eat
- Avoid salads, shellfish, crab and prawns
- Avoid fruit and vegetables which can't be peeled; fruits which can be peeled, eg, avocado, bananas, citrus fruits and melon, are safe
- Do not have ice in drinks and drink only bottled water. Do not use tap water, even for brushing teeth
If a traveller has spent a long time in tropical countries, it may be advisable for them to have a stool test on returning home as amoebae may be present without symptoms and require treatment.
Fact sheet provided by MIMS
Date last reviewed: June 2014