Atlas of foodborne infections
transmitted by contaminated food and water

Atlas of Patogens Contents Information sources Glossary Administration

Entamoeba histolytica

CZ: améby
EN: entamoeba

Occurrence:
Meat and Meat Products
Fish and Fish Products
Fruits and Vegetables
Water and Beverages


Category:
Parasites


Foodborne Disease:
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amebosis - gastrointestinal distress, dysentery (with blood and mucus); ulcerative and abscess pain.

Worldwide, with higher incidence of amebiasis in developing countries.  In industrialized countries, risk groups include male homosexuals, travelers and recent immigrants, and institutionalized populations.


Description:
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Several protozoan species in the genus Entamoeba colonize humans, but not all of them are associated with disease.  Entamoeba histolytica is well recognized as a pathogenic ameba, associated with intestinal and extraintestinal infections.  The other species are important because they may be confused with E. histolytica in diagnostic investigations.

Aa single celled parasitic protozoa, that infects predominantly humans and other primates. Diverse mammals such as dogs and cats can become infected but usually do not shed cysts (the environmental survival form of the organism) with their faeces, thus do not contribute significantly to transmission. The active (trophozoite) stage exists only in the host and in fresh faeces; cysts survive outside the host in water and soils and on foods, especially under moist conditions on the latter. When swallowed they cause infections by excysting (to the trophozoite stage) in the digestive tract.

Amebosis (or amoebiasis) is the name of the infection caused by E. histolytica. Infections that sometimes last for years may be accompanied by no symptoms, vague gastrointestinal distress, dysentery (with blood and mucus); ulcerative and abscess pain and, rarely, intestinal blockage. Onset time is highly variable. The amoeba's enzymes help it to penetrate and digest human tissues; it secretes toxic substances. Human cases are diagnosed by finding cysts shed with the stool. In heavy infections, the motile form (the trophozoite) can be seen in fresh faeces. Amebiasis is transmitted by faecal contamination of drinking water and foods, but also by direct contact with dirty hands or objects as well as by sexual contact. In the majority of cases, amoebas remain in the gastrointestinal tract of the hosts.

The infection is "not uncommon" in the tropics and arctics, but also in crowded situations of poor hygiene in temperate-zone urban environments. It is also frequently diagnosed among homosexual men. All people are believed to be susceptible to infection, but individuals with a damaged or undeveloped immunity may suffer more severe forms of the disease.


Pictures:

Entamoeba histolytica
Source: Life cycle of genus Entamoeba
Entamoeba histolytica
Source: trophozoit in feces
Entamoeba histolytica
Source: trophozoits in fecal smear

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