Download E. histolytica

Entamoeba
 Hazard Identification
 What 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 nonpathogenic.
 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 Foods
 E. 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 water
 Does 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 Characterisation
 Effects on Health
 E. 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 Outbreaks
 E. 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.
 Sources
 E. 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 Foods
 E. histolytica are relatively resistant to environmental factors,
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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 treatment
But the cysts are reported to be destroyed by 1% solutions of
sodium hypochlorite.
 Control Options
 Control measures for E. histolytica in food processing focus
largely on the 1- control of contamination in water and the 2management of infected food handlers.
 Processing
 Care 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.
 Hygiene
 Infected 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.
 Legislation
 E. histolytica is not usually mentioned specifically in food
safety and hygiene law.