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Jai Ganesh

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Registered: 2005-06-28

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Amoebiasis

Amobiasis

Gist

Amoebiasis, a type of gastro, is a cause of diarrhoea among travellers to developing countries. It is caused by a parasite known as Entamoeba histolytica that infects the bowel. Amoebiasis most commonly affects young to middle-aged adults. Proper handwashing helps prevent the spread of amoebiasis.

The mild form of amebiasis includes nausea (a feeling of sickness in the stomach), diarrhea (loose stool/poop), weight loss, stomach tenderness, and occasional fever. Rarely, the parasite will spread the body beyond the intestines and cause a more serious infection, such as a liver abscess (a collection of pus).

Summary

Amoebiasis is the second leading cause of death from parasitic disease worldwide. The causative protozoan parasite, Entamoeba histolytica, is a potent pathogen. Secreting proteinases that dissolve host tissues, killing host cells on contact, and engulfing red blood cells, E histolytica trophozoites invade the intestinal mucosa, causing amoebic colitis. In some cases amoebas breach the mucosal barrier and travel through the portal circulation to the liver, where they cause abscesses consisting of a few E histolytica trophozoites surrounding dead and dying hepatocytes and liquefied cellular debris. Amoebic liver abscesses grow inexorably and, at one time, were almost always fatal, but now even large abscesses can be cured by one dose of antibiotic. Evidence that what we thought was a single species based on morphology is, in fact, two genetically distinct species--now termed Entamoeba histolytica (the pathogen) and Entamoeba dispar (a commensal)--has turned conventional wisdom about the epidemiology and diagnosis of amoebiasis upside down. New models of disease have linked E histolytica induction of intestinal inflammation and hepatocyte programmed cell death to the pathogenesis of amoebic colitis and amoebic liver abscess.

Details

When the gut (intestine) becomes infected with the parasite Entamoeba histolytica (often shortened to E. histolytica), the condition is known as amoebiasis.

E. histolytica lives in the intestines of infected people. It can be passed out in their stools (faeces). Infection often occurs after someone drinks water contaminated by infected faeces or eats food prepared or washed using contaminated water. 9 out of 10 people with amoebiasis do not develop any symptoms. In those who do develop symptoms, diarrhoea, which can be bloody, is the most common symptom. This symptom is also known as amoebic dysentery.

Those most at risk of amoebiasis include travellers to areas where amoebiasis is common (mostly countries with poor sanitation).

Treatment includes medication to kill the amoebiasis parasite and drinking plenty of fluids to prevent dehydration. If diarrhoea develops and persists for more than a week or so after travelling abroad to places where E. histolytica is common, medical advice should be sought so that amoebiasis or other infections can be excluded.

What is amoebiasis?

Amoebiasis is a condition in which the gut (intestines) becomes infected with the parasite E. histolytica.

Entamoebae are a group of single-celled parasites (living things that live in, or on, other living organisms) 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 amoebiasis disease.

Amoeba histolytica

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.
* Other damp environments.

They move and feed by means of temporary arm-like extensions of their body called pseudopodia.

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 on its host, or obtain shelter using its host, but it contributes nothing to its host's well-being or welfare.

Human parasites include:

* Fungi.
* Protozoa, such as amoeba.
* Worms.

How do you develop amoebiasis?

E. histolytica lives in the intestine of infected people. It can be passed out in their stools (faeces).

The amoebiasis 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 (for example, 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 and start to multiply in their gut, and therefore amoebiasis can be passed on.

Physical relationship transmission of E. histolytica is also possible, usually in men who have gender with men.

E. histolytica is more likely to infect people who live in developing countries where sanitation and hygiene are poor or in tropical areas. 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. 1 in 10 people with amoebiasis will develop symptoms.

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 are infected with E. histolytica. As mentioned above, only about 1 in 10 of these will develop symptoms.

It is thought that, worldwide, about 40 to 50 million people infected with E. histolytica develop amoebic dysentery, colitis or abscesses, causing up to 100,000 deaths per year. It is the third most common death from parasites worldwide.

E. histolytica infection is particularly common in areas of Central and South America, Africa, and Asia.

Amoebiasis symptoms

Amoebiasis symptoms may be due to:

* Amoebic colitis

The E. histolytica parasite can cause inflammation of the lining of the intestines. This condition is known as amoebic colitis.

'Colitis' is a general term used for inflammation of the lining of the large intestine (the colon). '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.

* Diarrhoea.
* Amoebic dysentery

More severe inflammation with ulceration of the intestinal lining can occur in some people and this is called amoebic dysentery. (Dysentery is any infection of the intestines, causing severe bloody diarrhoea.)

Symptoms of amoebic dysentery include:

* Severe abdominal pain.
* Diarrhoea which often contains blood and mucus.
* High temperature (fever) may be another symptom but this is not common.
* Loss of appetite and weight loss.

Symptoms can last for several weeks. Some people with amoebic colitis may just develop bleeding from their back passage (rectal bleeding) with no diarrhoea.

Anaemia is a complication of amoebic dysentery (due to blood loss in the bloody diarrhoea).

Necrotising' colitis

Severe amoebic colitis is known as 'fulminant' or 'necrotising' colitis. The person is very unwell with:

* Very severe bloody diarrhoea,
* Very severe abdominal pain.
* A swollen (distended) abdomen with tenderness when their abdomen is examined.
* Fever is also present.
* Occasionally, a hole (perforation) through the wall of the intestine may occur.

This severe infection seems to be more common in certain groups of people, including:

* Children, particularly babies and toddlers.
* Pregnant women.
* People with underlying poor nutrition.
* People drinking over the recommended levels of alcohol.
* People with a diagnosis of cancer.
* People taking steroid medication.

Additional Information

Amoebiasis, or amoebic dysentery, is an infection of the intestines caused by a parasitic amoeba Entamoeba histolytica. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include lethargy, loss of weight, colonic ulcerations, abdominal pain, diarrhea, or bloody diarrhea. Complications can include inflammation and ulceration of the colon with tissue death or perforation, which may result in peritonitis. Anemia may develop due to prolonged gastric bleeding.

Cysts of Entamoeba can survive for up to a month in soil or for up to 45 minutes under fingernails. Invasion of the intestinal lining results in bloody diarrhea. If the parasite reaches the bloodstream it can spread through the body, most frequently ending up in the liver where it can cause amoebic liver abscesses. Liver abscesses can occur without previous diarrhea. Diagnosis is made by stool examination using microscopy, but it can be difficult to distinguish E. hystolitica from other harmless entamoeba species. An increased white blood cell count may be present in severe cases. The most accurate test is finding specific antibodies in the blood, but it may remain positive following treatment. Bacterial colitis can result in similar symptoms.

Prevention of amoebiasis is by improved sanitation, including separating food and water from faeces. There is no vaccine. There are two treatment options depending on the location of the infection. Amoebiasis in tissues is treated with either metronidazole, tinidazole, nitazoxanide, dehydroemetine or chloroquine. Luminal infection is treated with diloxanide furoate or iodoquinoline. Effective treatment against all stages of the disease may require a combination of medications. Infections without symptoms may be treated with just one antibiotic, and infections with symptoms are treated with two antibiotics.

Amoebiasis is present all over the world, though most cases occur in the developing world. About 480 million people are currently infected with about 40 million new cases per year with significant symptoms. This results in the death of between 40,000–100,000 people a year. The first case of amoebiasis was documented in 1875. In 1891, the disease was described in detail, resulting in the terms amoebic dysentery and amoebic liver abscess. Further evidence from the Philippines in 1913 found that upon swallowing cysts of E. histolytica volunteers developed the disease.

Signs and symptoms

Most infected people, about 90%, are asymptomatic, but this disease has the potential to become serious. It is estimated that about 40,000 to 100,000 people worldwide die annually due to amoebiasis.

Infections can sometimes last for years if there is no treatment. Symptoms take from a few days to a few weeks to develop and manifest themselves, but usually it is about two to four weeks. Symptoms can range from mild diarrhea to dysentery with blood, coupled with intense abdominal pains. Extra-intestinal complications might also arise as a result of invasive infection which includes colitis, liver, lung, or brain abscesses. The blood comes from bleeding lesions created by the amoebae invading the lining of the colon. In about 10% of invasive cases the amoebae enter the bloodstream and may travel to other organs in the body. Most commonly this means the liver,[10] as this is where blood from the intestine reaches first, but they can end up almost anywhere in the body.

Onset time is highly variable and the average asymptomatic infection persists for over a year. It is theorized that the absence of symptoms or their intensity may vary with such factors as strain of amoeba, immune response of the host, and perhaps associated bacteria and viruses.

In asymptomatic infections, the amoeba lives by eating and digesting bacteria and food particles in the gut, a part of the gastrointestinal tract. It does not usually come in contact with the intestine itself due to the protective layer of mucus that lines the gut. Disease occurs when amoeba comes in contact with the cells lining the intestine. It then secretes the same substances it uses to digest bacteria, which include enzymes that destroy cell membranes and proteins. This process can lead to penetration and digestion of human tissues, resulting first in flask-shaped ulcerations in the intestine. Entamoeba histolytica ingests the destroyed cells by phagocytosis and is often seen with red blood cells (a process known as erythrophagocytosis) inside when viewed in stool samples. Especially in Latin America, a granulomatous mass (known as an amoeboma) may form in the wall of the ascending colon or rectum due to long-lasting immunological cellular response, and is sometimes confused with cancer.

The ingestion of one viable cyst may cause an infection.

Steroid therapy can occasionally provoke severe amoebic colitis in people with any E. histolytica infection. This bears high mortality: on average more than 50% with severe colitis die.

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