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Amoebiasis / Amoebic Dysentery : Definition, Types, Causes, Symptoms, Diagnosis and general treatment of Amoebiasis/ Amoebic Dysentery

Amoebiasis is a common infection of the human gastro­intestinal tract. It has a world wide distribution. It is.a major health problem in the whole of Chi,na, South East and West Asia and Latin America, especially Mexico. Globally it was estimated that, in 1981, 480 million people carried E. histolytica in their intestinal tract and approximately one-tenth of infected people, i.e., 48 million suffered from invasive amoebiasis. It is probable that invasive amoebiasis, accounts annually for 40,000 to 110,000 deaths in the world (3). Prevalence rates vary from as low as 2 per cent to 60 per cent or more in areas devoid of sanitation (4). In areas of high prevalance. Amoebiasis occurs in endemic forms as a result of high levels of transmission and constant reinfection. Epidemic water-born infections can occur if there is heavy contamination of drinking water supply.

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 is a parasitic infection of the large intestine. Amoebiasis can affect anyone, most commonly affects young to middle-aged adults. The term "amoebiasis" has been defined as the condition of harbouring the protozoan parasite Entamoeba histolytica with or without clinical manifestations. The symptomatic disease occurs in less than 10 per cent of infected individuals.

The symptomatic group has been further subdivided into intestinal and extraintestinal amoebiasis. Only a small percentage of those having intestinal infection will develop invasive amoebiasis. The intestinal disease varies from mild abdominal discomfort and diarrhoea to acute fulminating dysentery. Extraintestinal amoebiasis includes involvement of liver (liver abscess), Iungs, brain, spleen, skin, etc. Amoebiasis is a potentially lethal disease. It carries substantial morbidity and mortality. It is the simplest organism of the animal kingdom which belongs to the class of Rhizopoda, order of Amoebida, genus of Entamoeba and species of E.Histolytica.

Causes of Amoebiasis

Amoebiasis is causes by a parasite that can live in humans without making them ill, or it can make a person very sick by going into organs like the liver or heart.

The parasite only lives in humans, and can be spread from person to person. People can get the disease by eating food, or drinking water that contain the parasite. A person may also spread the disease by not washing their hands after going to the toilet or changing a nappy, and then handling food for other people.

Amoebiasis is caused by potentially pathogenic strains of E. histolytica. Recent studies have shown that E. histolytica can be differentiated into at least 18 zymodemes (a zymodeme is a population of organisms differing from similar populations in the electrophoretic mobilities of one or more enzymes). It has furthermore been shown that pathogenic strains are all from particular zymodemes; that non, invasive strains are from quite distinct zymodemes; that invasive strains can give rise to faecal cysts, and the organisms breed true . The iso-enzyme characteristics do not, however, determine why a particular zymodeme is able to invade. Isoenzyme electrophoretic mobility analysis have so far identified 7 potentially pathogenic and 11 non-pathogenic zymodems.

Forms of Amoebasis / Amoebic Dysentery

E. histolytica exists in two forms - vegetative (trophozoite) and cystic forms. Trophozoites dwell in the colon where they multiply and encyst. The cysts are excreted in stool. Ingested cysts release trophozoites which colonize the large intestine. Some trophozoites invade the bowel and cause ulceration, mainly in the caecum and ascending colon; than in the rectum and sigmoid. Some may enter a vein and reach the liver and other organs.

The trophozoites are short-lived outside the human body; they are not important in the transmission of the disease. In contrast the cysts are infective to man and remain viable and infective for several days in faeces, water, sewage and soil in the presence of moisture and low temperature. The cysts are not affected by chlorine in the amounts normally used in water purification, but they are readily killed if dried, heated (to about' 55 deg C) or frozen.

How its spread

Amoebiasis may occur at any age. There is no sex or racial difference in the occurrence of the disease. Amoebiasis is frequently a household infection. When an individual in a family is infected, others in the family may a Iso be affected. Specific a ntiamoebic antibodies are produced when tissue invasion takes place. There is strong evidence that cell-mediated immunity plays an important part in controlling the recurrence of invasive amoebiasis . Amoebiasis occurs when the parasites are taken in by mouth. People with amoebiasis have Entamoeba hisolytica parasites in their faeces. The infection can spread when infected people do not dispose of their faeces in a sanitary manner or do not wash their hands properly after going to the toilet. Contaminated hands can then spread the parasites to food that may be eaten by other people and surfaces that may be touched by other people. Hands can also become contaminated when changing the nappies of an infected infant. Amoebiasis can also be spread by:

Faecal-oral route. This may readily take place through intake of contaminated water or food. Epidemic water-borne infections can occur if there is heavy contamination of drinking water supply. Vegetables, especially those eaten raw, from fields irrigated with sewage polluted water can readily convey infection. Viable cysts have been found on the hands.and under finger nails. This may lead to direct hand to mouth transmission.

Sexual transmission by oral-rectal contact is also recognized, especially among male homosexuals. (Hi) Vectors such as flies, cockroaches and rodents are capable of carrying cysts and contaminating food and drink.

Symptoms of Amoebiasis / Amoebic Dysentery

Most of the cases may not have any symptoms at all and function only as carriers and also function as spreaders, polluting the areas wherever they go. The disease symptoms usually start after a period of 7-15 days of infection which is called the incubation period. The symptoms are in two forms:

1. By burrowing the intestines and making ulcers, which bleed and cause anaemia or other diseases due to added infection
2. Absorbing the food from the host or letting out toxic substances in the intestines

Usually symptoms start with diarrhoea (watery stools) and abdominal pain (mostly in right hypochondrium)

Poor appetite or fear of food due to abdominal pain and loose stools

Later, with increased intensity of the infection, fever, nausea and bloody stools i.e. characteristic amoebic dysentery with slimy mucous occurs and complicate the condition

In due course, the patient loses weight and stamina

Sometimes allergic reactions can occur throughout the body, due to release of toxic substances or dead parasites inside the intestines.

Diagnosis of Amoebiasis / Amoebic Dysentery

Stool examination - Microscopic examination for identifying demonstrable E.H cysts or trophozoites in stool samples is the most confirmative method for diagnosis. Trophozoites survive only for a few hours, so the diagnosis mostly goes with the presence of cysts. But fresh warm faeces always show trophozoites. The cysts are identified by their spherical nature with chromatin bars and nucleus. They are noticed as brownish eggs when stained with iodine.
Biopsy also can point out E.H cysts or trophozoites.
Culture of the stool also can guide us for diagnosis.
Blood tests may suggest infection which may be indicated as leucocytosis (increased level of white blood cells), also it can indicate whether any damage to the liver has occurred or not.
Ultrasound scan - it should be performed when a liver abscess is suspected.

Treatment of Amoebiasis / Amoebic Dysentery

Symptomatic cases: At the health centre level, symptomatic cases can be treated effectively with metronidazole orally and the clinical response in 48 hours may confirm the suspected diagnosis. The dose is 30mg/kg/day, divided into 3 doses after meals, for 8-10 days. Tinidazole can be used instead of metronidazole. Suspected cases of liver abscess should be referred to the nearest hospital. (ii) Asymptomatic infections: In an endemic area, the concensus is not to treat such persons because the probability of reinfection is very high (3). They may however be treated, if the carrie is a food handler. In non-endemic areas they are always likely to h treated. They should be treated with oral diiodohyroxyquin, 650 ml t.d.s. (adults) or 30-40 mg/kg/day (children) for 20 days, or ore diloxanide furoate, 500 mg t.d.s. for 10 days (adults).

At present there is no acceptable chemoprophylaxis for amoebiasis. Mass examination and treatment cannot be considered solution for the control of amoebiasis.

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