• G. intestinalis was first noted by Antony van Leeuwenhoek:

 “All the particles aforesaid lay in a clear transparent medium, wherein I have sometimes also seen animalcules a-moving very prettily; some of ‘em a bit bigger, others a bit less, than a blood globule, but all of one and the same make.  Their bodies were somewhat longer than broad, and their belly was flatlike, furnisht with sundry little paws, where with they made such a stir in the clear medium and among the globules that you might e’en fancy you saw a pissabed (type of bug) running up against a wall; and albeit they made a quick motion with their paws, yet for all that they made but slow progress.”(4)


A Dutch tradesman born in 1632, van Leeuwenhoek is known as the “Father of Microbiology.”(2) He made this first known observation of (what is most likely) Giardia intestinalis when examining his own feces under his microscope.  Van Leeuwenhoek did not, however, make the connection between this observed creature and any pathology.

  • G. intestinalis was further studied and described by Vilem Lambl:

Two hundred years after van Leeuwenhoek, in 1859, a Czech physician named Vilem Lambl observed G. intestinalis in the stools of children with diarrhea, but believed the protazoa to be commensal and not responsible for the pathology (12).  The species was then named Giardia lamblia in his name. 


  • G. intestinalis recognized as pathogenic:

In the 1950s, a study done by RC Rendtorff identified infection in man after the introduction of small numbers of giardia cysts. (12,16)  In the 1960s, JD Karapetyan was able to culture G. intestinalis for the first time (12). Giardia was not confirmed as a pathogen until the late 1970s (1).