Entamoeba

Hazard IdentificationWhat is Entamoeba?Entamoeba is a single-celled protozoan parasite belonging to

the subphylum Sarcodina. The species important in human illness is Entamoeba

histolytica,

But several species are also found in humans, notably Entamoeba dispar, which is morphologically indistinguishable from E. histolytica, but much more common and non-pathogenic.

E. histolytica is also found in: non-human primates other mammals, including cats and dogs.

E. histolytica is an obligate parasite and requires a host in order to multiply.

It has been recognized as a cause of gastrointestinal disease (amoebiasis) in humans for many years and is found worldwide, but is particularly prevalent in developing countries.

E. histolytica has a two-stage life cycle, and exists in two forms. 1) Trophozoite: active stage multiplies within the gastrointestinal tract of the host. excreted in the host’s faeces but die quickly. Is not transmissible stage in the cycle

2) Cyst: Spore-like resistant cysts within the small intestine. excreted in the host’s faeces. transmissible stage in the cycle

Occurrence in FoodsE. histolytica is mainly associated with surface water that has

been polluted by human faeces.But cysts may also be present in a number of unprocessed

foods, including fruit and vegetables, if polluted water has been used for irrigation or processing.

E. histolytica:Does not grow in foods or in waterDoes not multiply in the environment outside of a suitable

host.

Cysts are destroyed by heat and E. histolytica is not normally associated with cooked and processed foods, unless recontamination from an infected food handler has occurred.

Any food that may come into contact with contaminated water or infected food handlers during production, and where there is no subsequent process that will destroy cysts, may be at risk from E. histolytica contamination.

However, food is not a major vehicle for the transmission of the parasite.

The waterborne and person-to-person transmission routes are thought to be much more common.

Hazard CharacterisationEffects on HealthE. histolytica can cause an acute gastrointestinal infection

(amoebiasis) in humans.Trophozoites:

Multiply in the gastrointestinal tract (particularly in the colon)

Occasionally invade the cells of the intestinal. Produce toxins.

Cyst: The cysts are infectious

The incubation time is usually between 1 to 4 weeks from ingestion of cysts.

The majority of cases are asymptomatic.But about 10% of those infected suffer mild gastroenteritis

symptoms of 1-slight diarrhoea and 2- abdominal discomfort.

In some cases, more severe symptoms “amoebic dysentery” and can be fatal : acute colitis bloody diarrhoea Fever

Immunocompromised individuals are particularly vulnerable to severe infections.

The infective dose is thought to be very low (in theory, a single cyst)

Incidence and OutbreaksE. histolytica is probably the most commonly reported

intestinal parasite worldwide.The true figure for the number of cases of infection with E.

histolytica is now estimated to be about 50 million worldwide. The infection is also estimated to cause between 50 000 and

100 000 deaths each year, mostly in developing countries. Waterborne and person-to-person transmission are more

important than foodborne outbreaks.

SourcesE. histolytica is an obligate parasite and thus originates from the

host. The primary source of E. histolytica is faeces of infected humans. Carriers may shed up to 15 million cysts each day in faeces. The cysts may be transferred to food via:

Infected food handler Polluted water used for irrigation or processing.

E. histolytica cysts are larger than those of Cryptosporidium (10–15 µm diameter) and are relatively easy to remove from water using modern water treatment methods, such as filtration.

Stability in FoodsE. histolytica are relatively resistant to environmental factors,

except heat and desiccation. E. histolytica cysts are destroyed by heating at temperatures

above 50 0C and by conventional milk pasteurisation. Therefore, most controlled cooking processes used in food

production should destroy any viable cysts in the product.The cysts are relatively resistant to chlorine at the levels used

in conventional water treatmentBut the cysts are reported to be destroyed by 1% solutions of

sodium hypochlorite.

Control OptionsControl measures for E. histolytica in food processing focus

largely on the 1- control of contamination in water and the 2-management of infected food handlers.

ProcessingCare should be taken to ensure that raw-food ingredients and

products that do not undergo further processing do not come into contact with contaminated surface water.

Fresh produce and other raw foods should only be washed/processed using potable quality water.

Heat processing is an effective control against E. histolytica cysts in food.

Normal milk-pasteurisation processes are effective, as are recommended ‘‘Listeria cook’’ processes for meat products (70 0C for at least 2 min).

Reheating cooked foods to at least 74 0C will destroy cysts immediately.

HygieneInfected food handlers are also a major contamination risk of

E. histolytica for foods that do not undergo any further processing, such as sandwiches and salads, and for the recontamination of cooked foods.

Good personal hygiene practice, especially hand washing, is an essential control and any staff suffering from gastroenteritis, especially following foreign travel, should be excluded from processing areas.

LegislationE. histolytica is not usually mentioned specifically in food

safety and hygiene law.