Giardiasis is a gastrointestinal infection caused by the parasite Giardia (lamblia). Transmission usually occurs from person to person or through contact with contaminated water.

What is Giardiasis?

Giardia lamblia is an intestinal parasite with a flagellum. Giardiasis is a parasitic infection of the intestines that occurs in humans and in many different animals and pets. Most of the Giardiastrains found in these animals are not contagious for humans. 


Giardiasis occurs in all ages. In healthy individuals, the infection does not cause any symptoms or gastrointestinal infection (gastroenteritis). Symptoms appear 1 to 3 weeks after infection:

  • diarrhea
  • abdominal cramps
  • nausea
  • gas and foul-smelling stools.

The symptoms disappear spontaneously in healthy individuals.

Giardiasis can cause chronic diarrhea, abdominal cramps, bloating, emaciation and fatigue. People with a weaker immune system may display a more serious illness that also lasts longer.


The disease occurs all over the world, but is particularly frequent in regions with poor hygiene because the parasite is excreted in the feces. The contamination occurs from person to person. or indirectly via food or water, or directly


The infection is mainly transmitted from person to person or via contaminated water.

To prevent transmission, hygiene regulations must be strictly followed. 

  • Wash and clean hands:
    • after going to the toilet to prevent spreading
    • after changing diapers
    • before cooking.
  • Clean the toilet, taps and door handles regularly
  • Use clean water and clean sanitary facilities. If this is not possible, like when you are on vacation, for example, only drink water that you know has been boiled/disinfected first.


Diagnosis is made by detecting the parasite in the stool or via an intestinal biopsy. It may be necessary to repeat this examination after a few weeks if no diagnosis could be made on the basis of the first stool sample.

Risk groups

The disease is more likely to be severe in patients with a weakened immune system.


Healthy individuals without symptoms do not need treatment. If necessary, individuals can be treated with metronidazole, which is an antiparasitic agent.

Sciensano plays a role in the epidemiological surveillance of Giardia in Belgium. This is done in cooperation with the laboratories and the regional authorities.

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