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Protozoal and fungal infections
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AGE  More common in early childhoodGENDER  Not significant factors
LIFESTYLE  Poor personal hygiene is a risk factorGENETICS  Not significant factors

Giardiasis is an intestinal infection with a protozoal parasite, often leading to diarrhoea.

© DK
This higly magnified image shows the parasite Giardia lamblia in a sample of tissue taken from the small intestine of a person with giardiasis.

Giardiasis is caused by a minute parasite known as Giardia lamblia, which infects the small intestine. Cysts (the dormant stages) of the parasite are excreted in the faeces of infected people and animals. The disease occurs mainly as a result of drinking water contaminated with cysts. The infection may also spread as a result of poor personal hygiene.

Infections are more serious in people with reduced immunity due to disorders such as HIV infection and AIDS or treatment with immunosuppressant drugs.

Giardiasis occurs mainly in developing countries. In developed countries, the infection usually affects children, walkers who drink from contaminated streams, and people who have returned from travelling in developing countries.

What are the symptoms of giardiasis?

Some people may not have symptoms, but, if symptoms do develop, they usually appear within 2 weeks of infection with the parasite and may include:

  • Diarrhoea.
  • Excessive flatulence and belching.
  • Bloating and abdominal pain.
  • Nausea.

If the symptoms last longer than a week, the infection may damage the lining of the small intestine, preventing the absorption of food and vitamins (see Malabsorption). This may result in weight loss and, in some cases, the blood disorder anaemia.

What might be done?

If your doctor suspects that you have giardiasis, you will probably be asked to provide a sample of faeces, which will be examined for the parasite cysts. If no parasites are found but your doctor still suspects you have the disease from your symptoms, he or she may recommend that you undergo upper digestive tract endoscopy to examine the inside of the small intestine. A sample of tissue or contents from the intestine may be removed during the procedure and examined under the microscope for evidence of infection. If giardiasis is diagnosed, your doctor will prescribe antibiotics, which usually kill the parasite in a few days. However, the infection may recur.

Can it be prevented?

If you are visiting a region where giardiasis occurs, you can prevent infection by boiling your drinking water for at least 10 minutes to kill the cysts. You should also follow strict standards of personal hygiene. Washing hands thoroughly after bowel movements and before preparing food should help to prevent the spread of the infection. You should avoid swimming unless you know the water is safe.


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