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Giardiasis is an infection of the small intestine (duodenum and jejunum) caused by the parasite Giardia lamblia. It can affect humans and animals. It can cause chronic diarrhoea and malabsorption.

Giardia exists worldwide including in developed countries, but is more common in areas with poor sanitation.


  • Giardia lamblia
  • Flagellate protozoan – lives in duodenum or jejunum.
  • Incubation= 7days-3months
Giardia Lamblia
Giardia Lamblia


Faecal-oral or from pets or birds (humans are main reservoir of infection). Can be trams
Typically from drinking water contaminated with giardia cysts (killed by boiling but NOT chlorination)


Prevalence approx. 20-30% in developing countries
Also significant numbers of cases seen in USA


Trophozoite parasite multiplies in upper bowel by binary fission – large areas of mucosa may be colonized in heavy infection
  • Disrupts brush-border and affects enzyme activity.
  • Stimulates inflammatory cytokine response, secretion of fluid and electrolytes and cell damage.
Trophozoites encyst as then pass through the intestine and become infective.

Clinical features

Most infections are asymptomatic. Acute phase lasts 2 – 4 weeks.
Symptoms are worse in immunodeficiency.
  • (Sometimes Explosive) watery diarrhea (NON-bloody)
  • mild abdominal pain
  • bloating and nausea
  • steatorrhoea
  • low grade fever
  • Chronic diarrhoea with HIV


  • Malabsorbtion
  • Lactose intoloerance
  • Dehydration
  • Weight loss
  • Chronic inflammation can lead to increased risk of cancer


  • Stool antigen
  • Culture of blood/ urine/stool/bone marrow/duodenal aspirates
  • Microscopy of stool for cysts and trophozoites.


Metronidazole or tinidazole


Good personal hygiene
Access to clean water.

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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