Oh Giardia!

Giardia lamblia (aka: G. duodenalis or G. intestinalis)

Don’t be tricked by these cute looking flagellated protozoans! They are often up to mischief, causing acute or chronic diarrhea with greasy foul-smelling stools, increased flatulence, abdominal pain, bloating, nausea and less commonly vomiting, fever, tenesmus, skin rashes and even swelling of joints. How can such a little creature cause such messy symptoms? By shear number. They cause mucosal damage as they try to adhere to the intestinal walls with their sucking disks. In addition, they create enzymatic messes, including thiol proteinases and lectins, which accumulate and cause destruction to the beautifully balanced brush border and flatten the villi. Inflammation of the mucosa causes cytokine release, resulting in the stimulation of the host immune system, turning this micro-battle into a messy war.

Life cycle: Giardia has two forms: an infectious cyst form that can survive in moist environments for long periods of time and a trophozoite form, which looks like the Giardia on the Daily Doodle. When cysts enter the GI tract, they transform into trophozites in the small intestine where they can stick to the intestinal walls using their suction disc. Note: they do not invade the mucosa epithelium, they just suction cup themselves to the surface. They can multiple through binary fission, creating multiples of themselves. The trophozoites that are unsuccessful at adhering to the surface are swept down to the large intestine where they transform back to a cyst in preparation for fecal excretion with the hope of infecting another unsuspecting person. How does Giardia accomplish its infectious goals? By transmission via cyst-contaminated water of food, direct fecal-oral transmission (PLEASE WASH YOUR HANDS!), direct person to person transmission and less commonly, direct animal to person transmission. It takes 1-4 weeks for the Giardia to incubate with onset of symptoms in 1-2 weeks.

Diagnosis: How can we catch these critters red-handed (of should I say, red-flagellated)? – by looking for trophozoites or cysts in fecal specimen, duodenal fluid or biopsy samples or by looking for Giardia antigens. Direct fluorescent antibody (DFA) staining is the “gold standard” for detection of Giardia cysts.

Treatment: Treat all symptomatic cases! Sometimes, Giardia infections are asymptomatic and treatment is not usually recommended, however, treatment may help reduce risk of transmission and comorbidities. The most widely used treatment is metroniazole (send Giardia away on the Metro-train…). It is recommended to avoid lactose-containing foods for at least one month after therapy because 20-40%  of patients develop lactose-intolerance which can last weeks or even months after treatment (1).

How can we help stop Giardia infections? By proper HAND-WASHING! For a quick review on proper hand-hygiene, click here.




  1. F. Munoz, “Treatment and prevention of giardiasis”. Uptodate.com. November 4, 2013. Link: http://www.uptodate.com/contents/treatment-and-prevention-of-giardiasis?detectedLanguage=en&source=search_result&search=giardia&selectedTitle=1~66&provider=noProvider
  2. K. Leder and P. Weller, “Epidemiology, clinical manifestations, and diagnosis of giardiasis”. Uptodate.com. November 5, 2013. Link: http://www.uptodate.com/contents/epidemiology-clinical-manifestations-and-diagnosis-of-giardiasis?detectedLanguage=en&source=search_result&search=giardia&selectedTitle=2~66&provider=noProvider
  3. Giardiasis. In DynaMed [application database]. EBSCO Information Services. November 4, 2013.


01/26/11 – “Giardia” by Michiko Maruyama. Medical Daily Doodle.

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