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GIARDIA LAMBLIA

Giardia lamblia is a microscopic single-celled (protozoan) parasite that causes illness in humans by infecting the intestines. The disease can be transmitted by direct contact with infected animals and humans, or by consumption of water, food or beverages contaminated by the faeces of infected humans or animals. The illness caused by giardia infection is termed giardiasis.

Life Cycle

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the faeces. The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the faecal-oral route (hands or fomites). In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites). Trophozoites then multiply by longitudinal binary fission, remaining in the small intestine where they can be free or attached to the mucosa by a ventral sucking disk. Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in non-diarrhoeal faeces. Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible.

Incubation Period & Duration

Incubation Period
Usually 1 - 2 weeks (average 7 days).

Duration
Normally the illness lasts for 1 to 2 weeks, but there are cases (more commonly in adults) of chronic infections lasting months or even years. Chronic cases, both those with defined immune deficiencies and those without, are difficult to treat.

Symptoms

The initial short-lived acute phase:

gas or flatulence
nausea
abdominal cramps
diarrhoea - initially frequent and watery but later becomes bulky, sometimes frothy, greasy and offensive. Stools may float on water.

The subsequent chronic phase:

malaise
weight loss
dehydration
stools usually pale or yellow and are frequent and of small volume
occasionally episodes of constipation intervene, with nausea and diarrhoea brought about by the ingestion of food. Some people with giardiasis have no symptoms at all i.e. they are asymptomatic.

Sources/Associated Foods

Although Giardia is found in soil, food, or surfaces that have been contaminated with the faeces from infected humans it is most frequently associated with the consumption of contaminated water.
Foods implicated in foodborne outbreaks include fresh produce such as noodle salad, fruit salad, ice and raw sliced vegetables. These outbreaks were traced to food contaminated by infected food handlers. Cool moist conditions favour the survival of the organism.

Spread

Transmission routes are:

the consumption of contaminated water (primarily) and food (less commonly)
contact by animal-to-human (e.g. farm visits) or human-to-human (particularly in households and nurseries)
recreational exposure to contaminated water or land

Swallowing the parasite in any of the following ways may lead to infection:

Accidentally putting something into your mouth or swallowing something that has come into contact with faeces of a person or animal infected with Giardia
Swallowing recreational water contaminated with Giardia
Eating uncooked food contaminated with Giardia
Accidentally swallowing Giardia picked up from surfaces (such as bathroom fixtures, changing tables, nappy buckets, or toys) contaminated with faeces from an infected person.

The incidence of giardiasis is higher in (young) child day care centres that serve food, due to the potential for spread from nappy changing activities.
Spread within families is common.

Control

Practice good personal hygiene (especially hand washing) and protect others by not using or swimming in recreational waters if you are experiencing diarrhoea (essential when children are in nappies) and for at least 2 weeks after diarrhoea has stopped. This latter advice is because you can still contaminate water after your symptoms have ended. Indeed, outbreaks of giardiasis among recreational water users have been caused via this route.

Avoid water that might be contaminated
For example:

Do not drink untreated water from shallow wells, lakes, rivers, springs, ponds, and streams.
Do not drink untreated water during community-wide outbreaks of disease caused by contaminated drinking water.
Do not use untreated ice or drinking water when travelling in countries where the water supply might be unsafe.

Avoid food that might be contaminated

Wash and/or peel all raw vegetables and fruits before eating.
Use safe, uncontaminated water to wash all food that is to be eaten raw.
Avoid eating uncooked foods when travelling in countries that only have minimal water treatment and sanitation systems.

Exclusion/Return to Work Parameters

Cases in risk groups 1- 4 not to return until 48 hours after first normal stool.

[Group 1 - food handlers; Group 2 - health care workers; Group 3 - children under 5 in nurseries etc.; Group 4 - older children and adults who may find it difficult to implement good standards of personal hygiene]

Additional Information

Since 1986, in England and Wales there have been an average of about 5250 cases per year, with many being associated with foreign travel.
The overall incidence of infection in the United States is estimated at 2% of the population.
There may be up to 10⁷ (10 million) cysts per gram of faeces when excreted. The cysts are resistant to (adverse) environmental conditions.
Ingestion of just 25 - 100 cysts may cause disease, as contrasted to most bacterial illnesses where hundreds to thousands of organisms must be consumed to produce illness.
The disease mechanism is unknown at present, although current theories include:

that the organism produces a toxin
the organism obstructs the absorptive surface of the intestine
that there is some sort of synergistic relationship with some of the intestinal flora.

Giardiasis is more prevalent in children than in adults, possibly because many individuals seem to have a lasting immunity after infection.
Persons more likely to become infected include:

children who attend day care centres
child care workers
parents of infected children
international travellers
people who swallow water from contaminated sources
backpackers, hikers, and campers who drink unfiltered, untreated water
swimmers who swallow water while swimming in lakes, rivers, ponds, and streams

Giardia lamblia is the most common human parasite in developed countries.

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Friday 10 September 2010