Giardia

Hazard IdentificationWhat is Giardia?Giardia is a single-celled flagellate protozoan parasite

belonging to the order Diplomonadida.The cells are unusual in having two nuclei. The species important in human illness is Giardia intestinalis

(previously referred to as G. lamblia, or G. duodenalis).

G. intestinalis is also found in a number of animals, including cattle, cats and dogs.

G. intestinalis is an obligate parasite and requires a host in order to multiply.

It is a cause of gastrointestinal infection (giardiasis) in humans and some other animals, and is found worldwide.

G. intestinalis has a two-stage life cycle, and exists in two forms.

1) Trophozoite: Pear-shaped flagellated 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 FoodsG. intestinalis is mainly associated with surface water that has been

polluted by human or animal faecesBut cysts have also been found in a number of unprocessed foods,

including: Root crops Lettuce Strawberries

G. intestinalis: 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 G. intestinalis is not normally associated with cooked and processed foods.

Any food that may come into contact with contaminated water during production, and where there is no subsequent process that will destroy cysts, may be at risk from G. intestinalis 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 that foodborn rout.

Hazard CharacterisationEffects on HealthG. intestinalis can cause an acute gastrointestinal infection in

humans.Children are especially vulnerable to infection. The mechanism by which it causes disease is unclear. The trophozoites probably attach to the epithelial cells lining

the gut, but do not invade the cells. They may produce a toxin in the small intestine, but this has

not been confirmed. The incubation time for the infection is usually between 1–3

weeks from ingestion of cysts.

The main symptom are: Diarrhoea Abdominal pain. Fever

In healthy adults, symptoms typically last for 1–2 weeks.The infection is generally self-limiting in most cases, but drug

treatment is sometimes required.However, in immunocompromised individuals, infection can

be more serious and long lasting, requiring hospital treatment, and occasional deaths have been recorded.

The infective dose is thought to be very low and ingestion of as few as 10 cysts.

Incidence and OutbreaksG. intestinalis is probably the most commonly reported

intestinal parasite in the developed world.The European countries with the highest reported incidence:

Estonia (24.28 cases per 100 000 people) Iceland (14.65 cases per 100 000 people)

The results also show that children aged 0–4 years were most commonly infected.

There are seasonal peaks of infection in spring and autumn. There were 20075 reported cases of giardiasis in the USA in

2005.

SourcesG. intestinalis is an obligate parasite and thus originates from

the host. The primary source of G. intestinalis is the faeces of infected

humans and animals, which may contain up to 109 cysts in a single day.

The cysts are extremely infectious and may be transferred to food via an infected food handler, or through polluted water used for crop irrigation or processing.

G. intestinalis cysts are larger than those of Cryptosporidium (9–12 µm diameter) and are relatively easy to remove from water using modern water treatment methods.

They are also less resistant to chlorine, but are not inactivated by the concentrations normally used to treat water.

They are much less likely to pass through water-treatment plants into the public water supply system.

Stability in FoodsG. intestinalis cysts are generally resistant to environmental

factors. Cysts can persist for months in cool and moist conditions. However, there is little information on their survival and

inactivation in foods.The cysts are relatively resistant to some sanitisers and

disinfectants, notably chlorine and ozone.G. intestinalis cysts are not heat resistant and are destroyed by

conventional milk pasteurisation. A temperature of 60–70 0C for 10 min is reported to inactivate

cysts completely.

Therefore, most controlled cooking processes used in food production should destroy any viable cysts in the product.

Oocysts can survive for significant periods at temperatures below 0 0C, especially in water

But frozen storage is reported to cause inactivation.

Control OptionsControl measures for G. intestinalis in food processing focus

largely on the control of contamination in water and the 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 should be obtained from suppliers practicing good agricultural practice.

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

Heat processing is an effective control against G. intestinalis cysts in food.

Normal milk-pasteurisation processes are effective, as are recommended ‘‘Listeria cook’’ processes for meat products (700C for at least 2 min).

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

Freezing foods for at least 7 days is also an effective control.

HygieneInfected food handlers are also a major G. intestinalis

contamination risk for foods that do not undergo any further processing, such as sandwiches and salads.

Good personal hygiene practice, especially hand washing, is an essential control .

Any staff suffering from gastroenteritis should be excluded from processing areas.

LegislationIt is not usually mentioned specifically in food safety and

hygiene law.