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Page last reviewed: 13/07/2011

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).

Diarrhoea is the most common symptom of giardiasis. Other symptoms can include vomiting, abdominal cramps, bloating and foul-smelling wind. Although these symptoms are often very unpleasant, giardiasis doesn't usually pose a serious threat to health. It can be easily treated.  

Read more about the symptoms of giardiasis.

When to see a doctor

You should visit your GP if you have symptoms of diarrhoea, cramps, bloating and nausea that last for more than a week.

Your GP may have to send some stool samples to be tested in a lab to confirm a diagnosis of giardiasis, but usually it's easily treated with medicine that kills the giardia parasite.

Read more about treating giardiasis.

How is giardiasis spread?

Most people become infected with giardiasis by drinking water that's contaminated with the parasite.

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 contaminated water.

Who is affected?

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

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

There are around 60 to 70 cases of giardiasis reported in Ireland each year. But the true number is likely to be higher as many cases go undiagnosed.

Around one third of cases are thought to be contracted abroad, but the person doesn't develop the symptoms until they return home.

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.

Risk areas for 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)

Page last reviewed: 13/07/2011

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 and abruptly or they can develop slowly over the course of a number of days.

Initial symptoms can include:

  • watery diarrhoea, which can be foul-smelling and explosive
  • abdominal cramps
  • vomiting
  • a mild high temperature of between 37-38ºC (98.6-100.4ºF)
  • producing foul-smelling wind (farts)
  • nausea (feeling sick)
  • bloating
  • indigestion
  • fatigue (extreme tiredness)
  • loss of appetite
  • weight loss, which can be as much as 4.5kg (10 pounds)

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

A small number of people go on to develop long-term (chronic) giadiasis, 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.

When to seek medical advice

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

If your child has diarrhoea, contact your GP if your child passes six or more watery stools in the space of 24 hours, or if their symptoms of diarrhoea persist for more than five days.

Dehydration is an excessive loss of fluids and minerals from the body.
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
Loss of appetite
Loss of appetite is when you do not feel hungry or want to eat.
Nausea is when you feel like you are going to be sick.
The sac-like organ of the digestive system. It helps to digest food by churning it and mixing it with acids to break it down into smaller pieces.

Page last reviewed: 13/07/2011

Giardiasis is caused by microscopic parasites known as Giardia intestinalis. The parasites live in the intestines of humans and animals. Most human infections are 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 goes to the toilet (passes a stool), some of the cysts inside the intestines can be passed out of the body inside the stool (faeces).

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

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

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 particularly in environments where there are many babies who frequently need their nappies changing, such as day care centres and nurseries.

There have been a number of cases where hikers and campers have developed giardiasis after drinking contaminated water from streams and lakes. Therefore, 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.

Sexually active gay men have an increased risk of contracting giardiasis as the giardia parasite can be passed from the anus (inside the bottom) to the mouth during sexual intercourse.  

A cyst is a fluid-filled sac or cavity in the body.

Page last reviewed: 13/07/2011

Giardiasis can be diagnosed by checking a person's stools (faeces) for giardia cysts.

A stool sample is usually sent to the microbiology laboratory in your nearest hospital to be tested.

Up to three stool samples may need to be taken over a number of days as giardia cysts aren't always passed out of the body each time you go to the toilet. If someone has typical symptoms of giardiasis, and the first sample tests negative, further samples may need to be tested in order to be certain.

Further testing

If repeated stool samples are negative but symptoms, such as bloating or pain continue, an endoscopy (telescopic examination of the intestines) may be recommended. Samples taken during the endoscopy may show the giardia parasite.

Page last reviewed: 13/07/2011

Giardiasis can usually be successfully treated using a medicine called metronidazole, which works by killing the parasites that cause the infection.

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 GP 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 rare (occurring in less than 1 in a 1,000 people).

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

  • nausea
  • vomiting
  • diarrhoea
  • stomach pain


If you're unable to take metronidazole, for example, you've previously had an allergic reaction to it, an alternative medication called tinidazole may be recommended.

Most people only need a one to three-day course of tinidazole. The risk of side effects is slightly higher, although these tend to be mild and improve as your body gets used to the medication. 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


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.
As a precaution, using metronidazole or tinidazole is not recommended during the first three months of pregnancy or if you're breastfeeding.

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 GP will be able to tell you if treatment is necessary.

Page last reviewed: 13/07/2011

Severe symptoms of diarrhoea can lead to rapid fluid loss and dehydration. Therefore it's important to keep drinking while you're sick.  

Dehydration is a potentially serious problem in the developing world where access to sources of clean water may be limited.

Symptoms of dehydration include:

  • dry, wrinkled skin
  • an inability to urinate
  • irritability
  • sunken eyes
  • in babies and young children - no tears being produced when they cry, and wetting their nappies much less that you'd expect

Dehydration can be treated by increasing fluid intake and using a type of treatment known as oral rehydration solution (ORS). ORS usually comes in sachets that are available over-the-counter from your local pharmacist. You dissolve them in water and they help to replace salt, glucose and other important minerals that your child loses through dehydration.



Malnutrition is a potential complication of long-term giardiasis. Malnutrition happens when the body doesn't receive enough nutrients. 

One of the main symptoms of malnutrition is unexplained weight loss. For most average adults, losing around a stone without trying to could be a sign of malnutrition.

In children, especially younger children, failure to grow (in weight and height) at the expected rate can be a sign of malnutrition.

Mild to moderate cases of malnutrition can be treated with a high-energy diet and dietary supplements.

More serious cases (which are uncommon - especially when associated with giardiasis) may require treatment in hospital.

Page last reviewed: 13/07/2011

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 and dry them with a clean towel. You should also encourage your children to wash their hands regularly.

Water safety

In Ireland, water purification systems makes 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's 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 that the bottle is properly sealed before using it.

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

Preventing the spread of infection

If you're diagnosed with giardiasis (or even if you have any 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're a sexually active gay man, 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).

Straight men and women who also have frequent anal sex also have an increased risk of infection.

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. 

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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