The frequency with which Giardia lamblia invades the biliary system and actually gains entrance to the gallbladder is still an unanswered question.
Clinical observations by ourselves and other workers1 have definitely verified the fact that giardial organisms are often found in the B fraction of bile obtained by the Meltzer-Lyon technic of duodenal drainage. This fact does not prove, however, that the parasites actually do invade the gallbladder. Hollander2 has pointed out that the hypertonic solution which is introduced into the duodenum to obtain the B fraction of bile causes liberation of fluid into the duodenal lumen and that this fluid may wash the giardial organisms from the deep crypts of the duodenal mucosa into the lumen and thus account for the presence of the parasites in the duodenal aspirate.
Reports of cases in the literature in which giardial parasites have been obtained from bile from the gallbladder
Hartman HR, Kyser FA, Comfort MW. INFECTION OF THE GALLBLADDER BY GIARDIA LAMBLIA. JAMA. 1942;118(8):608–609. doi:10.1001/jama.1942.62830080001010