What is giardiasis, and how does one get it?

Written by: Dr Aathavan Loganayagam
Edited by: Conor Lynch

This article sheds light on a medical condition known as giardiasis, an illness which animals spread to humans. On hand to tell us more about the disease, including the symptoms, diagnosis, and treatment, is revered London-based consultant gastroenterologist, Dr Aathavan Loganayagam

What is giardiasis?

Giardiasis is a zoonotic disease (one passed from animals to humans) caused by a flagellate protozoan, Giardia lamblia. Encased in a hard, shell-like cyst, the organism is found in the digestive tract of humans and many animals (domestic and wild).


How does one get giardiasis?

People can only become infected with giardia by swallowing the parasite, but it takes as few as 10 cysts to cause infection. Anything that comes into contact with faeces from infected humans or animals can become contaminated with giardia, but it is usually spread by: 


  • touching contaminated surfaces such as bathroom taps or door handles
  • drinking water containing the parasite
  • accidentally swallowing infected water while swimming
  • eating uncooked food that contains the parasite
  • contact with someone who has giardiasis


Once inside their host, the microscopic cysts rapidly multiply. An infected person can shed millions of cysts a day in their faeces.


Where exactly is giardia found in the world?

Giardia occurs worldwide, particularly during the summer months. People are particularly prone to infection when travelling in countries where the parasite is common in its human and animal populations.


The highest incidence is in South and Central Asian countries, where it’s estimated that one in three people have or have had giardia. It is also quite common in the Middle East and South America. However, giardiasis also occurs in developed countries. In fact, it’s the most common internal parasitic disease affecting humans worldwide.


What are the main symptoms?

Symptoms of giardiasis normally appear after between one to two weeks after infection, but can occur as quickly as two days. In otherwise healthy people, symptoms of giardiasis may last from between two to four weeks. For those with few or no symptoms, giardia infection can clear up completely without treatment in a fortnight.


However, giardia can result in diarrhoea (often with foul-smelling, greasy stools), abdominal cramps, bloating, flatulence, fatigue, and nausea. Typically, there is a gradual onset of two to five loose stools per day and increasing fatigue.


Sometimes, upper gastrointestinal symptoms are more prominent, and weight loss may also occur over time. Fever and vomiting, however, are quite uncommon. Some sufferers, particularly infants and pregnant women, are at higher risk of dehydration.


How is giardiasis diagnosed?

For severe symptoms or persisting diarrhoea, a stool sample is needed to be collected and sent to the laboratory for testing. Until recently, up to three stool samples were required. Since most cases of giardia are found in the first sample, only one sample is needed nowadays.


How is the illness treated?

Medication containing tinidazole, metronidazole, nitazoxanide, paromomycin, furazolidone, or quinacrine, can reduce the symptoms of giardiasis and speed up recovery.


How can one prevent getting giardiasis?

Following the safe food and water guidelines is the best way to prevent giardia. If you are uncertain if water you intend to drink is safe, first boil it for one minute and allow it to cool before drinking. Chemical disinfectants or filters are also effective.


One of the most important and effective ways to avoid illness is regular hand washing, especially before handling food.


Dr Aathavan Loganayagam is a highly qualified and skilled consultant gastroenterologist who specialises in giardiasis amongst many other gastrointestinal-related medical conditions. Schedule an appointment with him today via his Top Doctors profile.

By Dr Aathavan Loganayagam

Dr Aathavan Loganayagam trained in medicine at Guy’s, King's and St. Thomas’ medical schools. He then underwent rigorous structured specialty training in gastroenterology and general internal medicine in the well respected South London training programme.

He then spent two years during postgraduate training as a research and endoscopy fellow at Guy’s and St Thomas’ Hospitals, London. His research was in the fields of pharmacogenetics, inflammatory bowel disease and gastrointestinal malignancy. He has received awards and grants for outstanding research work, including the prestigious NHS Innovation London Award.

Dr Loganayagam has numerous publications in peer reviewed journals on all aspects of gastroenterology. He is actively involved in clinical research. He has particular local expertise in the practice of personalised medicine and the utilisation of novel therapeutic agents in the treatment of complex inflammatory bowel disease. He is currently the lead clinician for endoscopy at Queen Elizabeth Hospital, Woolwich.

Diagnostic and advanced therapeutic endoscopy remains a major part of his clinical expertise, including assessment and treatment of inflammatory bowel disease, strictures, polyps and cancers.

Dr Loganayagam is an approachable doctor who takes pride in his communication skills with patients. He is keen to ensure that patients are fully informed and involved in all aspects of their care.

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