Organism

Amoebiasis is infection caused by the single celled organism Entamoeba histolytica. This organism has 2 forms: the fragile adult amoeba and a hardy cyst form. The infection can involve either the gut, causing amoebic dysentery, or cause abscesses in other parts of the body, usually the liver.

Mode of Transmission

Amoebiasis is transmitted via food or water contaminated by faeces containing amoebic cysts. One common source of infection is lettuce grown in fields fertilised using 'night soil' (human faeces) or washed in contaminated water. Transmission can also occur sexually by oro-anal contact. Individuals with amoebic dysentery are less infectious than might be expected since they pass few cysts; most transmission occurs from asymptomatic individuals who produce large numbers of cysts. Cysts can survive for weeks or months in a moist environment outside the body.

Regions affected

Amoebiasis occurs world-wide, but is particularly associated with areas of poor sanitation and hygiene in the tropics. Outbreaks can occur in households and institutions.

Prevention

Individuals can avoid becoming infected with amoebiasis by avoiding uncooked vegetables, salads and unboiled water while travelling in the tropics. Hygiene, including hand washing is important. Sexual practices that promote the spread of amoebae should be avoided. Individuals known to be carrying the infection and producing cysts should be treated with antibiotics.

At a community level, it is important to provide adequate sanitation facilities and to protect public water supplies by filtration or boiling water for more than a minute. Chlorination of public water supplies is not always effective.
Immunisation

None available.

Symptoms/Signs

Many infections are asymptomatic but may result in chronic carriage of the organism, with great potential for transmission. Amoebic dysentery is an illness characterised by diarrhoea with blood and mucus, abdominal pain and fever. The incubation period may be as long as several months or more, but is usually 2-4 weeks. Once bowel symptoms appear they may rapidly become more severe with bowel perforation or major bleeding; alternatively, the diarrhoea may come and go over prolonged periods.

Amoebic abscesses occur after bowel infection (which may be asymptomatic or mild), following spread of the organism in the blood stream. They usually occur in the liver, but may rarely be found in the lungs, spleen or brain. Liver abscesses present typically with fever, liver enlargement and mild pain and tenderness over the site of the abscess.

Tests

Amoebiasis is diagnosed by finding amoebae in fresh stool samples. As the adult amoeba lives only for a short period outside the bowel, stool samples must be examined within an hour of being produced. The bowel can contain other types of amoeba which may be confused with Entamoeba histolytica; definitive diagnosis depends on finding red blood cells within the amoeba (a sign that the organism is penetrating the bowel wall and causing disease) or seeing the characteristic cyst form of Entamoeba histolytica.

Patients with amoebic liver abscesses may continue to shed amoebic cysts in their stool samples. Antibody tests are almost always positive in patients with amoebic abscesses, but are less reliable in amoebic dysentery. Amoebic abscesses can be visualised using ultrasound or CAT scans: a characteristic scan appearance coupled with a positive antibody response may be considered to be diagnostic.

Treatment

Acute amoebic dysentery and amoebic abscesses should be treated with the antibiotic Metronidazole.


Source:www.privatehealth.co.uk
Last Editorial Review: 25/1/2010