What is a parasite?
A parasite is a general term for any living thing that lives in, or on, another living organism. It may feed of its host, or obtain shelter using its host, but it contributes nothing to its host’s well-being or welfare. Human parasites include fungi, bacteria, viruses, protozoa and worms.
What is amoebiasis?
Amoebiasis is when your intestines (gut) become infected with the parasite Entamoeba histolytica (often abbreviated to E. histolytica). Entamoebae are a group of single-celled parasites that can infect both humans and some animals. There are at least six species of Entamoeba that can infect the human gut but only E. histolytica causes disease.
E. histolytica is an amoeba. An amoeba is the name given to any single-celled microscopic animal with a jelly-like consistency and an irregular, constantly changing shape. Amoebae are found in water, soil and other damp environments. They move and feed by means of flowing extensions of their body, called pseudopodia. Amoebae are a type of protozoa. Protozoa is a more general name for microscopic, single-celled organisms. Some protozoa, including E. histolytica, are important parasites of humans.
How do you get amoebiasis?
E. histolytica lives in the intestines (gut) of infected people. It can be passed out in their stools (faeces). The parasite can actually survive for weeks, or even months, in soil, fertiliser, or water that is contaminated with infected faeces. If another person then drinks the contaminated water or eats contaminated food, they too can become infected.
E. histolytica can also be present on the hands of an infected person if they follow poor hygiene practices (e.g. not washing and drying their hands properly after going to the toilet). If they are then in contact with another person, or prepare food for others, the parasite can enter another person’s mouth, start to multiply in their gut, and therefore amoebiasis can be passed on. Sexual transmission of E. histolytica is also possible, usually in men who have sex with men.
E. histolytica is more likely to infect people who live in developing countries where sanitation and hygiene is poor. In the UK, most people with E. histolytica infection have caught it whilst travelling abroad.
Most people who become infected with E. histolytica do not develop any symptoms. However, symptoms may develop if the parasite causes inflammation of the lining of your gut. In some people, E. histolytica can also get into the bloodstream from the gut and spread around the body to the liver, lungs and sometimes other organs. Note: the parasites can still be present in the stools of infected people who have no symptoms.
How common is amoebiasis?
It is estimated that around 1 in 10 people in the world is infected with E. histolytica. As mentioned above, not everyone develops symptoms. It is thought that, worldwide, about 40 to 50 million people infected with E. histolytica develop amoebic colitis or abscesses causing up to 100,000 deaths per year.
E. histolytica infection is particularly common in areas of Central and South America, Africa, and Asia. If you travel to such areas you may be at risk of infection. Ways to prevent infection are described below.
What are the symptoms of amoebiasis?
About 9 out of 10 people who are infected with E. histolytica have no symptoms. If infection does cause symptoms, they may be due to:
This is when the E. histolytica parasite causes inflammation of the lining of your intestine. ‘Colitis’ is a general term used for inflammation of the lining of the colon (the large intestine). ‘Amoebic’ refers to the fact that the colitis is caused by the amoeba E. histolytica. The disease is often mild and can just lead to abdominal pain and diarrhoea. However, more severe inflammation with ulceration of the intestinal lining can occur in some people and so-called ‘amoebic dysentery’ can develop. (Dysentery is any infection of the intestines, causing severe diarrhoea with blood and mucus.)
So, symptoms of amoebic dysentery include severe abdominal pain and diarrhoea which can contain blood and mucus. Fever may be another symptom but this is not common. You may also experience loss of appetite and weight loss. Symptoms can last for several weeks. Some people with amoebic colitis may just develop rectal bleeding (bleeding from their back passage) with no diarrhoea.
Severe amoebic colitis is known as ‘fulminant’ or ‘necrotising’ colitis. The person is very unwell with very severe bloody diarrhoea, very severe abdominal pain and a distended abdomen with tenderness when their abdomen is examined by a doctor. Fever is also present. Occasionally, perforation of the intestine (a hole in the intestine) may occur. This severe infection seems to be more common in certain groups of people, including the very young, pregnant women and those with underlying poor nutrition.
In a few people with amoebic colitis, an ‘amoeboma’ can develop. This is essentially a mass (or lump) of tissue that builds up or forms in the wall of the intestine due to the inflammation. It may cause a blockage of the intestine. Anaemia is another complication of amoebic colitis (due to blood loss in the bloody diarrhoea).
Note: if you develop diarrhoea after travelling abroad to places where E. histolytica is common, you should see your doctor so that amoebiasis or other infections can be excluded.
Amoebic liver abscess
This is when the E. histolytica parasite invades right through your gut wall, gets into your bloodstream, and passes in your bloodstream to your liver. Once in your liver, it can cause an amoebic liver abscess to form. (An abscess is any localised collection of pus in the body that is surrounded and walled off by damaged and inflamed tissues.) An amoebic liver abscess contains pus and liquified, dying liver tissue.
Symptoms include fever and right upper abdominal pain with tenderness in this area when a doctor examines you. You may become jaundiced and your liver may also become enlarged (again, a doctor may be able to tell this when they examine your abdomen).
Only 3-4 out of 10 people with an amoebic liver abscess have symptoms of amoebic colitis at the same time. However, many people with a liver abscess may recall an episode of bloody diarrhoea within the previous year. So, an amoebic liver abscess can develop some time after initial infection with E. histolytica. It can be many years in some people.
Spread from an amoebic liver abscess
Rarely, an amoebic liver abscess can rupture (burst) and lead to damage to your diaphragm (the thin muscle that separates your chest cavity from your abdominal cavity). This can allow spread of the abscess into your chest cavity, affecting your lungs and your pleura (the membrane that covers your lungs). Symptoms of such a complication include cough, difficulty breathing and pain in your chest when you breathe in.
Also, very rarely, in someone with an amoebic liver abscess, infection can spread to their brain and central nervous system. This can be very serious and needs quick treatment. Symptoms include headache, nausea, vomiting and confusion.
How is amoebiasis diagnosed?
Amoebiasis may be diagnosed when the E. histolytica parasite is seen in your stools after a stool sample is sent to the laboratory and examined under a microscope. Ideally, three stool specimens from different days should be examined. However, in many people with an amoebic liver abscess, E. histolytica may not be seen in their stools. Sometimes the parasite can be seen when fluid is drawn out of a liver abscess and examined under a microscope. A needle is passed through your skin into the abscess, usually using an ultrasound scan to guide the person performing the procedure.
Other methods to detect E. histolytica in your stools have also been developed, including stool antigen detection (looking for E. histolytica proteins in your stools). The infection may also be diagnosed using a blood test that looks for evidence of E. histolytica infection in your blood. (If you have infection, antibodies to E. histolytica are usually found in your blood. These are another type of protein that are made in response to E. histolytica antigen.)
Sometimes a colonoscopy is performed if you have bloody diarrhoea and other tests have been negative. A colonoscopy is when a thin, flexible telescope is passed through your anus into your colon to allow examination of your colon. A biopsy (tissue sample) taken at colonoscopy and examined under the microscope can show the parasites in your intestinal lining.
A liver ultrasound scan or a CT scan of your liver can show a liver abscess. Other tests may also be carried out if you have amoebic colitis or an amoebic liver abscess; for example, blood tests to look at your liver function, blood tests to look for anaemia, etc.
What is the treatment of amoebiasis?
If you have no symptoms but are found to have E. histolytica in a stool specimen, it is usually advised that you should be treated with medication to kill the parasite. The drug diloxanide furoate is commonly used. Treatment is advised because you can still pass on the infection to others even if you have no symptoms. The amoebae will still pass out in your stools. Also, you may still develop symptoms at a later stage.
The treatment of symptomatic amoebiasis then depends on your symptoms.
Antibiotics are needed to treat amoebic colitis. Metronidazole is the usual antibiotic that is used but tinidazole may be a good alternative. A second drug, usually diloxanide furoate, is then used to get rid of any parasites that may still be living in your gut. After treatment is completed, testing of a follow-up stool sample is advised to ensure that the parasites have been cleared.
If you have amoebic colitis, you are at risk of becoming dehydrated. Dehydration is when there is a lack of fluid in your body. It can occur if the water and salts that are lost in your stools are not replaced by your drinking adequate fluids. Therefore, drinking plenty of fluids is very important if you have amoebic colitis. Your doctor will advise you about how much fluid and what type of fluids you should drink.
You may be given special rehydration drinks. They are made from sachets that you can buy from pharmacies. (The sachets are also available on prescription.) You add the contents of the sachet to water. Rehydration drinks provide a good balance of water, salts, and sugar. The small amount of sugar and salt helps the water to be absorbed better from the gut into the body. They do not stop or reduce diarrhoea. Do not use home-made salt/sugar drinks, as the quantity of salt and sugar has to be exact.
If you do become severely dehydrated, you may need admission to hospital so that you can be given fluids intravenously (through a vein).
Occasionally, someone who develops fulminant colitis or bowel perforation may need surgery to remove part of their intestine.
Amoebic liver abscess
Antibiotics are also needed to treat an amoebic liver abscess. The same antibiotics are used and are usually very effective, clearing the abscess in most people. Again, a second drug, usually diloxanide furoate is then used to get rid of any parasites that may still be living in your gut. If you also have colitis symptoms, drinking plenty of fluids is essential, as described above.
If a very large amoebic liver abscess develops, or antibiotic treatment is not successful, surgery may be needed to drain the abscess. Surgery may also be needed if the liver abscess ruptures.
Preventing the spread of amoebiasis to others
If you or your child has amoebiasis, the following are recommended to prevent the spread of infection to others:
- Wash your hands thoroughly after going to the toilet. Ideally, use liquid soap in warm running water, but any soap is better than none. Dry your hands properly after washing. If your child wears nappies, be especially careful to wash your hands after changing nappies and before preparing, serving, or eating food.
- If a potty has to be used, wear gloves when you handle it, dispose of the contents into a toilet, then wash the potty with hot water and detergent and leave it to dry.
- Don’t share towels and flannels.
- Don’t prepare or serve food for others.
- If clothing or bedding is soiled, first remove any faeces into the toilet. Then wash in a separate wash at as high a temperature as possible.
- Regularly clean with disinfectant the toilets that you use. With hot water and detergent, wipe the flush handle, toilet seat, bathroom taps, surfaces and door handles at least once a day. Keep a cloth just for cleaning the toilet (or use a disposable one each time).
- You should stay off work, school, college, etc, while you have amoebiasis. Your doctor will advise you when it is safe to return. Avoid contact with other people as far as possible during this time.
- Food handlers: if you work with food and develop diarrhoea or vomiting, you must inform your employer and immediately leave the food-handling area. If amoebiasis is confirmed, you should inform your employer and stay away from work until your doctor advises it is safe to return.
If you have amoebiasis infection and you work with vulnerable groups of people such as the elderly, the unwell or the young, you should inform your employer.
What is the prognosis (outlook) for amoebiasis?
Most people who develop amoebic colitis or an amoebic liver abscess can be successfully treated with drugs to kill the parasite and eliminate it from the intestine. Occasionally, drug treatment does not get rid of the parasite completely and symptoms can recur.
In rare cases, fulminant colitis can develop and this causes severe illness and carries a worse outlook. If an amoebic abscess ruptures, or infection spreads to the central nervous system, again this has a worse prognosis.
If strict hygiene measures are not undertaken and precautions are not used when travelling to ‘at-risk’ areas, re-infection can occur.
Can amoebiasis be prevented?
In general, good hygiene is essential to prevent the spread of many infections to others and to reduce your chance of picking up infections from others.
Handwashing is the most important thing that you can do. In particular, always wash your hands and dry them thoroughly, and teach children to wash and dry theirs:
- After going to the toilet (and after changing nappies or helping an older child to go to the toilet).
- Before preparing or touching food or drinks.
- Before eating.
If you smoke, you should also wash your hands before smoking. The simple measure of washing and drying hands regularly and properly is known to make a big difference to the chance of developing many infections.
In addition to this, when travelling to areas with poor sanitation, you should avoid eating or drinking the following to help reduce your chance of getting amoebiasis. This is because amoebiasis is often passed on by drinking contaminated water or eating contaminated food. Avoid:
- Tap water
- Watered down fruit juices (for example, fruit juices that may be sold in the street)
- Ice cream
- Ice cubes
- Raw or undercooked meat
- Fruit that has already been peeled
- Mayonnaise or sauces
Sealed bottled water, tea, coffee and alcohol are thought to be safe to drink.
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