Health Centres - Amoebic dysentery
What is amoebic dysentery?
Amoebic dysentery (amoebiasis) is an infection of the intestine (gut) caused by an amoeba called
Amoebae are parasites that are found in contaminated food or drink. They enter the body through the mouth when the contaminated food or drink is swallowed. The amoebae are then able to move through the digestive system and take up residence in the intestine and cause an infection.
There are several different species of amoebae, but the most dangerous, such as
How do you get amoebic dysentery?
- as free amoebae (known as 'trophozoites')
- as infective cysts, which are a group of amoebae surrounded by a protective wall, that have been passed (excreted) in the carrier's faeces (human or animal).
If you swallow contaminated food that contains the free amoebae (trophozoites) hardly anything is likely to happen, because they usually die in the stomach on account of its acidity. On the other hand, cysts are particularly resistant to the acidic contents of the stomach and food contaminated with cysts represents a genuine risk of infection.
When the cysts reach the intestine of another person the individual amoebae are released from the cysts and are able to cause infection.
Amoebic dysentery is passed on by careless or negligent hygiene where contaminated food and drink is consumed without adequate heat treatment.
Salads washed with contaminated water are a common method of spread.
What does amoebic dysentery feel like?
Amoebic dysentery may not demonstrate any symptoms for long periods of time (months, even years). However, infected individuals still excrete cysts and, consequently, infect their surroundings.
When the amoebae attack, they damage the walls of the large intestine, causing ulceration and subsequent bleeding. The milder symptoms of this are stomach cramps (colic), painful passage of stools (tenesmus) and bloody, slimy diarrhoea, which is often foul smelling. However, the course of the disease can become complicated and alter radically if the amoebae break through the intestinal wall and its lining (peritoneum), causing peritonitis (inflammation of the peritoneum).
What can you do to help yourself?
In practice, the only way to avoid infection with amoebic cysts is to ensure that everything you eat or drink has been washed or sterilised properly and cooked thoroughly.
Drinking water can be made safe in two ways:
- by boiling it for 10 to 15 minutes (a little longer at high altitudes), and then cooling it rapidly and keeping it covered.
- by adding water-purifying tablets and then leaving the mixture to stand for at least 15 minutes before use.
Chemical methods of sterilisation do not, however, guarantee complete destruction of all possible harmful organisms.
Foods to avoid include salads, unpeeled fruit and ice cream. Ice cubes may also have been made with contaminated water, so avoid having drinks that contain ice cubes unless you are certain that the water used to make them has been sterilised.
Diagnosis
Anyone who develops bloody diarrhoea should see a doctor as soon as possible and ensure that they tell the doctor they have been travelling in the tropics, as amoebic dysentery does not normally occur in the UK.
In the presence of the classic symptoms of amoebic dysentery, the diagnosis can often be made by means of a stool analysis. If there are complications then further investigations, such as ultrasound, may be needed to confirm the diagnosis.
Bloody diarrhoea is seen in many other illnesses, but in tropical areas the diagnosis will typically be either amoebic dysentery or shigellosis (bacillary dysentery which is caused by bacteria).
Treatment
Amoebic dysentery is treated with metronidazole. Complications, such as perforation of the intestinal wall or the presence of abscesses within the body's organs, require specialist hospital treatment.
In an emergency, for instance if you have bloody diarrhoea and are on holiday in the tropics and cannot get medical help, you can treat yourself with metronidazole, eg two 400mg tablets, three times a day for five days. This is the dose for adults who are neither pregnant nor breastfeeding.
It is important to avoid drinking alcohol during treatment. Even if you have to treat yourself, it is important to see a doctor to ensure that the treatment has been truly effective.
As metronidazole requires a prescription, you could ask your own doctor to write a prescription in advance if you know that you will be travelling to remote tropical areas where access to a doctor or hospital may be difficult.
Such prescriptions need to be issued privately, ie the cost of the drug has to be paid in full to the pharmacist.
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