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


Faecal-oral/ from pets or birds
(humans are main reservoir of infection)
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 fissionàlarge areas of mucosa may be colonized in heavy infection
àDisrupts brush-border and affects enzyme activity.
àStimulates inflammatory cytokine response àsecretion 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
low grade fever
Chronic diarrhea with HIV


lactose intoloerance
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) currently works as a GP Registrar and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University. 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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