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Giardiasis (gee-ar-dye-a-sis) is an infection of the digestive system caused by tiny parasites called Giardia intestinalis (also known as Giardia lamblia, or Giardia duodenalis).

is the most common symptom of giardiasis.

Other symptoms can include abdominal cramps, bloating and

. Although these symptoms are often unpleasant, giardiasis doesn't usually pose a serious threat to health and can be easily treated.

Read more about the

symptoms of giardiasis

When to see a doctor

See your doctor if you have symptoms of diarrhoea, cramps, bloating and nausea that last for more than a week, particularly if you've recently travelled abroad.

Your doctor may have to send some samples of your faeces to be tested in a laboratory to confirm a diagnosis of giardiasis. Up to three samples may need to be taken over a number of days to help ensure a correct diagnosis.

Giardiasis is usually treated successfully with

medicine that kills the giardia parasite. In most cases, medicines called metronidazole or tinidazole are used.

Read more about

treating giardiasis

How is giardiasis spread?

Most people become infected with giardiasis by drinking water contaminated with the Giardia parasite, or through direct contact with an infected person.

The giardiasis infection can also be passed on if an infected person doesn't wash their hands properly after using the toilet, then handles food that's eaten by others. Food can also be contaminated if washed with infected water.

Practising good hygiene – such as regularly washing your hands with soap and water – and taking care when drinking water in countries with poor levels of sanitation can help to reduce your risk of developing giardiasis.

Read more about the

causes of giardiasis
preventing giardiasis

Who is affected?

Giardiasis occurs almost everywhere in the world, but is particularly widespread where access to clean water is limited and sanitation is poor.

It can affect people of all ages but is most common in young children and their parents. This is because activities such as nappy changing increase the risk of infection.

Most cases of giardiasis are one-off, but small outbreaks can sometimes occur in households, among family members, or at nurseries. Larger outbreaks are usually traced to contaminated water sources, such as drinking wells or water parks.


The symptoms of giardiasis usually begin 4-10 days after a giardiasis infection has occurred, but they can appear up to three weeks later.

They can begin suddenly or they can develop slowly over a number of days.

Common symptoms include:

You may also experience vomiting and a mild fever of 37-38ºC (98.6-100.4ºF), although these symptoms are less common.

If left untreated, the symptoms can persist for around one or two months before gradually improving.

A small number of people develop long-term (chronic) giardiasis, which causes persistent or repeated bouts of diarrhoea that can last for up to two years. In children, long-term giardiasis can result in a failure to grow at the expected rate. The medical term for this is failure to thrive.

However, long-term giardiasis is rare among people who have been treated for the condition.

Read more about

treating giardiasis

When to seek medical advice

Visit your doctor if you have symptoms of diarrhoea, cramps, bloating and nausea that last for more than a week.

If your baby or child has diarrhoea that has lasted for more than two or three days, or they have had six or more episodes of diarrhoea in the last 24 hours, you should take them to see your doctor.


Giardiasis is caused by microscopic parasites known as Giardia intestinalis.The parasites live in the intestines of humans and animals. In most cases, the infection is caught from other humans.

In most cases, the parasites don't cause any symptoms, and people have no idea that they're infected. In parts of the world where giardiasis is widespread, an estimated one in five people could be infected.

How giardiasis is spread

While inside the intestines, the parasites form a hard protective shell known as a giardia cyst.

When someone with the giardiasis infection passes faeces, some of the cysts inside the intestines can be passed out of the body inside the faeces.

Giardia cysts can survive outside the body for several weeks or months.

Once outside the body, giardiasis is usually spread by drinking water that's been contaminated with infected faeces. This most commonly occurs in countries that have poor sanitation and limited access to clean water.

Giardiasis can also be spread through direct contact between people.

Less commonly, giardiasis is spread when an infected person doesn't wash their hands properly after going to the toilet and transfers the parasites onto surfaces, utensils or food. Anyone who touches an infected surface, uses infected utensils, or eats contaminated food can transfer the parasites into their mouth and become infected.

Who's at risk?

Parents or childcare workers who change the nappy of a baby with giardiasis have an increased risk of developing the condition by accidentally transferring infected faeces into their mouth.

The risk is higher in environments where there are many babies and frequent nappy changing, such as day care centres and nurseries.

There have been a number of cases of hikers and campers developing giardiasis after drinking contaminated water from streams and lakes. You should always avoid drinking untreated water (water that hasn't been boiled or chemically treated) even if it looks clean.

A small number of outbreaks of giardiasis have been linked to recreational water areas, such as water parks and swimming pools, which have become contaminated with the giardiasis parasites.

People travelling to parts of the world where standards of water hygiene are poor have an increased risk of developing giardiasis. However, due to the time it takes for symptoms to appear after becoming infected, most people won't have any symptoms until they return home.

People who have regular anal sex are also at an increased risk of contracting giardiasis, as the giardia parasite can be passed from the anus (back passage) to the mouth during sexual intercourse.

Read about

preventing giardiasis
for advice about reducing your risk of developing the condition.


Giardiasis can usually be successfully treated with medicines that kill the parasites responsible for the infection.


Most commonly, an

called metronidazole is used.

It is usually taken in tablet form (orally). The recommended course of treatment will depend on factors such as your age and body weight, but it can range from a three- to 10-day course.

Your doctor or pharmacist will be able to give more detailed instructions for your individual circumstances.

Metronidazole is well tolerated in adults and children. Serious side effects are relatively rare.

The most commonly reported side effects are usually mild ones affecting the digestive system, such as:

Metronidazole can also cause dizziness and drowsiness (see below).


A medicine called tinidazole is sometimes used as an alternative to metronidazole.

Most people only need one dose of tinidazole. Like metronidazole, tinidazole can have an adverse effect on the digestive system. Side effects include:

  • nausea
  • vomiting
  • loss of appetite
  • diarrhoea
  • stomach pain or cramps
  • headache
  • tiredness
  • unpleasant metallic taste in your mouth
  • darkening of your urine

See [giardiasis medicines information] for more information about metronidazole and tinidazole.


On rare occasions, some people feel dizzy or sleepy while they're taking metronidazole. If this happens to you, avoid driving or using power tools or machinery.

Don't drink alcohol while taking metronidazole or tinidazole, or for 48 hours after finishing your dose. Mixing alcohol with these types of medication can make the side effects worse.

Metronidazole should be used with caution if you're pregnant or breastfeeding, as advised by your doctor.

If you're diagnosed with giardiasis, other members of your household may be advised to have treatment. This may be recommended as a precautionary measure just in case they've also been infected. Your doctor will be able to tell you if treatment is necessary.


Giardiasis can often be prevented by practising good hygiene and taking some common-sense precautions.

Wash your hands

The most effective way to prevent giardiasis is to wash your hands regularly, particularly:

  • after going to toilet
  • after changing a nappy
  • before handling and eating food

Wash your hands with soap and water for at least 15 to 20 seconds, making sure that you clean the front and back of your hands. After washing your hands, rinse, then dry them with a clean towel. You should also encourage your children to wash their hands regularly.

Water safety

Water purification systems make it very unlikely that tap water could be contaminated by giardiasis. However, avoid drinking untreated water from rivers and lakes in this country and when travelling abroad.

Recreational facilities, such as swimming pools, paddling pools and water parks can sometimes become contaminated, particularly if they're used by younger children who may accidentally soil themselves while in the water. Avoid drinking the water when using such a facility. Giardia parasites can survive in chlorinated water, so you should not assume that chlorinated water is safe.

If you're going camping, it is recommended that you boil water before drinking it.

Travelling abroad

If you're travelling to countries where giardiasis is widespread and sanitation is poor, drink bottled water only. Make sure the bottle is properly sealed before using it. You should also use bottled water when brushing your teeth.

Also avoid eating raw fruit and vegetables as they may have been handled by someone with giardiasis.

Places where giardiasis is widespread include:

  • sub-Saharan Africa – all the countries south of the Sahara Desert, such as South Africa, Gambia and Kenya
  • south and southeast Asia, particularly India and Nepal
  • Central America
  • South America
  • Russia
  • Turkey
  • Romania
  • Bulgaria
  • the countries of the former Yugoslavia (Croatia, Serbia and Montenegro, Slovenia, Macedonia, and Bosnia and Herzegovina)

Preventing the spread of infection

If you're diagnosed with giardiasis (or even if you have an episode of diarrhoea that's not diagnosed), it's very important to take precautions to prevent other members of your household becoming infected. You should:

  • wash your hands regularly
  • not cook or handle food that will be eaten by other members of your household
  • avoid sharing utensils or towels

It's recommended that you stay away from work or college and avoid swimming pools until you have been completely free of symptoms for 48 hours. Similarly, your child should stay away from school or nursery until they have been completely free from symptoms for 48 hours.


If you have frequent anal sex, make sure that you wash your hands after handling a condom that's been used during anal sex and after touching the anus (back passage).

The sexual practice known as ‘rimming’, in which one partner kisses or licks the other partner’s anus, also leads to an increased risk of infection. Due to the increased risk of giardiasis and other types of infection, this practice is not recommended.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.