Reviewed by Saskia Knight, Nutritionist
On 22 Jan 2025
What is Giardia lamblia?
Giardia lamblia (also known as Giardia duodenalis) is a parasite that infects the small intestine, causing giardiasis, a gut infection characterised by prolonged watery diarrhoea, stomach cramps, and bloating which can typically last for 6 weeks. It is highly contagious and one of the most common intestinal parasites worldwide and affects both humans and animals.
Giardia is spread through a number of ways, mostly through contaminated food, water, or close contact with an infected person or animal.
How does Giardia lamblia spread?
Giardia lamblia spreads when someone swallows the parasite’s cysts through contaminated food, water, or direct contact with another individual or animal that has been infected. The cysts, which act as a protective outer shell, allow the parasite to survive outside the body for weeks to months (for example, in soil or water). Once ingested, the cysts 'hatch' in the small intestine, releasing the active form of the parasite, which attaches to the gut lining and causes infection.
Common ways Giardia can spread:
Contaminated water: Drinking or accidentally swallowing untreated water from rivers, lakes, or wells is a common source of infection, especially during camping or hiking trips. Drinking water contamination is more common in developing countries where water treatment infrastructure may be less advanced or effective.
Contaminated food: Raw or unwashed fruits and vegetables, particularly those that have been washed with untreated water, can be contaminated with Giardia.
Contaminated surfaces: Touching surfaces that have been touched by an infected person.
Person-to-person transmission: The parasite spreads easily in environments such as nurseries, care homes, and households. Poor hand hygiene after using the toilet or changing nappies can lead to infections spreading to others. It can also be spread during sexual intercourse, particularly anal and oral sex.
Animal contact: Infected animals, including pets, livestock, or wildlife, can carry Giardia cysts in their faeces, which can contaminate water sources or surfaces.
Is Giardia found in the UK?
Yes, Giardia is present in the UK. In 2017, there were 4,793 reported cases of giardiasis in England and Wales, making it the most common intestinal parasite infection in the region.
What symptoms does Giardia lamblia cause?
Giardiasis can cause many uncomfortable digestive symptoms that usually appear 1 to 2 weeks after exposure to the parasite. However, side effects can affect individuals differently with some people not experiencing any symptoms at all.
Common symptoms:
- Watery diarrhoea
- Stomach cramps and bloating
- Nausea or vomiting
- Fatigue
- Loss of appetite
- Weight loss
- Greasy or pale stools that float (due to poor fat absorption)
- Excessive gas and belching
Giardia Lamblia, Cryptosporidium, Cyclospora and many other types of gut parasites can share many of the same symptoms. Parasites will typically cause a number of unpleasant digestive symptoms.
How long does Giardiasis last?
If treated promptly with medication, symptoms usually resolve within a few days to a week. However, without treatment, giardiasis can last for several weeks or even months. In some cases, symptoms may appear to improve but then return (known as relapsing symptoms).
Can you have Giardia without symptoms?
Yes, some people can carry Giardia without showing any symptoms (asymptomatic carriers). However, even without symptoms, they can still spread the parasite to others through poor hygiene.
When should you seek medical advice?
You should seek medical attention if you experience:
- Diarrhoea lasting more than 7 days
- Severe stomach pain or bloating
- Signs of dehydration (dry mouth, dizziness, or little to no urination)
- An inability to keep food or fluids down due to vomiting
- Unintentional weight loss
Who is most at risk of Giardia infections?
While giardiasis can affect anyone, some groups are more high-risk than others.
Travellers: People visiting regions with poor sanitation or untreated water supplies.
Campers and hikers: Those drinking untreated water from rivers, lakes, or streams.
Children in nurseries or daycare settings including workers and carers: Giardia spreads easily in these environments.
How is Giardiasis diagnosed?
The only way to diagnose Giardia is through a stool test which checks for the cysts of the parasite in the stool. The parasites cysts can appear intermittently so may not be present in every stool, therefore it is recommended to test multiple stool samples over a few days to confirm the presence of Giardia.
Our recommended testing method is PCR (Polymerase Chain Reaction) testing which we find to be the most accurate method to detect Giardia DNA in the stool.
Our gut parasite stool test identifies 22 types of parasites, pathogenic bacteria and viruses, making it one of the most advanced tests available in the UK.
The gut parasite test can also be paired with our comprehensive gut microbiome test kit, to provide you with a full picture of your gut health. The gut microbiome test will provide you with a detailed report on your overall gut health as well as personalised recommendations on nutrition and supplements to help increase your gut diversity.
How to Test for Giardia lamblia at home
Whilst you can take a stool sample at home, it will need to be sent to a lab for testing to identify the parasite within your stool.
Home stool sample kits allow you to collect a stool sample easily and send it to a lab for analysis. These non-invasive tests can identify the presence of parasites like Giardia and provide results within a few days.
We recommend testing for a wide range of parasites, pathogenic bacteria and viruses to help get to the bottom of any symptoms that you are experiencing.
How is Giardiasis treated?
Giardiasis usually requires antibiotics to help clear the infection. If left untreated, the infection can persist for weeks or even months, however with antibiotics such as Metronidazole, the infection can clear within just 7 days.
In rare cases, alternatives or a longer course of treatment may be needed if the infection is severe or if symptoms relapse.
References
https://www.gov.uk/research-for-development-outputs/drugs-for-treating-giardiasis-192197
What helps with recovery?
Since Giardia can cause an imbalance in the gut microbiome, it’s important to support your recovery with gut-friendly foods and maintain adequate hydration.
Foods to eat:
High fibre diet: Including foods like - fruits, vegetables, whole grains, nuts, legumes, and seeds. Introduce fibre to your diet slowly and remember to drink plenty of fluids.
Probiotic-rich foods: Yoghurt, kefir, and fermented vegetables help replenish healthy gut bacteria that may have been destroyed during antibiotic treatment.
Hydrating fluids: Oral rehydration solutions (ORS) or drinks containing electrolytes help prevent dehydration.
Foods to avoid:
Alcohol, caffeine, greasy foods, spicy foods, and sugary snacks, as they can irritate the gut and worsen diarrhoea symptoms.
Read our guide on good gut foods for a full breakdown of foods that can help to improve your gut health.
Can Giardia infections be prevented?
While it is difficult to completely avoid exposure to Giardia, you can reduce your risk by following a number of safeguarding measures.
Food safety:
Wash fresh fruits and vegetables thoroughly.
Cook food thoroughly, as heat kills the parasite.
Water safety:
Drink bottled, boiled, or filtered water when travelling in high-risk areas.
Avoid swallowing water when swimming in lakes, rivers, or public swimming pools.
Hygiene:
Wash your hands thoroughly with soap and water after using the toilet and before eating or preparing food.
Teach children good hygiene habits to prevent the spread of infections in nurseries and schools.
The role of gut health in recovery
A healthy gut microbiome can support recovery from Giardia infections by helping to reduce inflammation and strengthen your immune system. Eating a balanced diet that includes probiotic and prebiotic foods can help rebalance your gut bacteria after infection.
Reference
https://pmc.ncbi.nlm.nih.gov/articles/PMC7835142/
Conclusion
Giardia lamblia is a common intestinal parasite that spreads through contaminated food, water, and direct contact. While infections can cause unpleasant digestive symptoms, giardiasis is treatable with medication and usually resolves quickly with the right care. By practising good hygiene, following food and water safety guidelines, and supporting your gut health, you can reduce your risk of infection and recover more effectively if you become infected.
It is important to note that many different types of parasites may cause similar symptoms, so when testing for a parasite, you should try and test for many different types at the same time. Other common parasites that we test for include, Cryptosporidium, Cyclospora and Entamoeba histolytica.
