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Giardiasis (giardia)

3-minute read

Key facts

  • Giardiasis is an infection of the small intestine, spread by hand to mouth contact with the giardia parasite from infected water or faeces.
  • You may have no symptoms, but some people can have diarrhoea, stomach cramps and nausea that may last for months.
  • If you have giardiasis, you should drink plenty of water.
  • You may need to take antibiotics.
  • You can prevent giardiasis by practicing good hygiene and boiling untreated water before drinking, for example if you travel to countries with poor water quality.

What is giardiasis?

Giardiasis is an infection of the small intestine caused by a parasite called giardia. It can cause long-lasting symptoms and serious problems, especially in children. It’s one of the most common waterborne diseases worldwide.

What are the symptoms of giardiasis?

The most common symptoms are:

  • diarrhoea, which may be pale, greasy and smelly
  • stomach cramps or bloating
  • excessive gas or flatulence (wind)
  • nausea
  • fatigue

Symptoms of giardiasis start 3 to 25 days after infection with the parasite. They may last for months (especially if left untreated) and long-term effects may include significant weight loss and malnutrition. Some people can develop irritable bowel syndrome after having giardiasis. Some people do not develop symptoms but they can still pass the disease to others.

CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

What causes giardiasis?

Giardiasis is caused by the parasite giardia duodenalis, also known as giardia lamblia or giardia intestinalis.

You can catch giardiasis if you swallow contaminated:

  • water
  • food
  • faeces (poo)

Outbreaks are common in childcare centres if carers practice poor hygiene after changing nappies.

Travellers and hikers can be infected from drinking or swimming in contaminated water.

Some countries have poor water quality and food hygiene practices, so you need to be careful when visiting these countries. You should not drink untreated water from rivers or lakes anywhere.

How is giardiasis diagnosed?

If you think you or your child has giardiasis, see your doctor. They may send a sample of your stool (poo) to be tested for giardia.

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How is giardiasis treated?

Many people with giardiasis get better without treatment. Your doctor may need to prescribe antibiotics.

People with diarrhoea, especially babies and young children, need to drink plenty of fluids to avoid dehydration. Your doctor may recommend rehydration therapy of glucose / electrolyte solution, or diluted fruit juice for children who refuse this solution.

Can giardiasis be prevented?

To help prevent the spread of giardia, always practice good personal hygiene, for example:

  • Wash hands properly, especially after going to the toilet, before handling food and after every nappy change.
  • Do not share linen, towels or eating utensils with other people who have symptoms.
  • Boil water before drinking if you suspect contamination.
  • Keep infected people from childcare, pre-school, school or work until they have not had any diarrhoea for at least 24 hours.
  • Do not use swimming pools for at least 2 weeks after diarrhoea has completely stopped.

Treating infected people reduces the spread of the giardia parasite.

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Last reviewed: July 2022


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Giardiasis is an infection mainly of the small intestine caused by the parasite Giardia lamblia. Giardiasis has been reported in humans and in a variety of animals. To prevent infection wash hands thoroughly and don't drink untreated water.

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