Giardiasis is a gastrointestinal infection caused by a single celled microscopic parasite called Giardia lamblia. This parasite can be carried by both people and animals. It is a common cause of both childhood and travellers' diarrhoea. The infection is, however, more commonly found in children than adults.

Although the parasite has a global distribution it has been found to be the major cause of childhood diarrhoea in developing countries and is also very common in Eastern Europe and across the USA.

The infection can present with a range of symptoms including diarrhoea, nausea, flatulence, stomach cramps, indigestion and loss of appetite. It is thought that about 15% of infected people show no symptoms at all. However where they do occur these symptoms can last for several weeks leading to dehydration and a loss of weight. In underdeveloped countries where the patient may already be malnourished such dehydration and loss in weight may lead to death.

Direct contact with an infected host is not required for transmission as the parasite is able to survive an extended time in the environment in the form hardy cysts. Ingestion of only a few of these cysts can lead to infection. It can survive in water but is killed by the chlorination process common in potable water treatment plants. It has been found in rivers, ponds, lakes and even Jacuzzis!

Fruit, vegetables and salads that have come into contact with soil contaminated with human or animal waste and then inadequately washed is another common source of infection. Giardia can also be transmitted by contact with objects such as contaminated towels or toilet seats.

Although, as has been stated, it can be found globally certain groups of people are more commonly infected by the parasite. These are travellers to developing countries where there may be inadequate washing facilities. Children in nurseries where there can be direct faecal contamination as a consequence of this their adult care givers are also at a higher risk of infection. Also couples involved in certain sexual practices where direct faecal-oral transmission is possible are at a higher risk.

The time between ingesting the parasite and the start of the symptoms is usually 7 to 15 days but it may be as short as 5 days or as long as 4 weeks.

Diagnosis requires laboratory examination of stool samples where both the cysts and the motile forms of the parasite can be detected microscopically. As excretion of the parasite can be intermittent multiple tests may be required before diagnosis is confirmed.

Although some people recover without any treatment in others the symptoms can persist for an extended time, sometimes weeks or possibly even months. Fortunately the parasite is susceptible to antibiotics and patients can be cured with a course of a suitable drug such as metronidazole. While taking this drug patients must refrain from drinking alcohol.

As with all infections prevention is better than treatment. Good hygiene practices, a protected or treated source of drinking water along with the proper preparation of fruit and vegetables will markedly reduce the number of people catching this little parasite.

Learn more about this author, Alison Bowler.
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