An ultrastructural analysis of changes in surface architecture of intestinal mucosa following Giardia lamblia infection in mice.

The oral inoculation of Giardia lamblia trophozoites (Portland 1 strain) resulted in the establishment of infection by day 3-5 in NMRI mice. By 9-11 days postinfection, the trophozoites load reached maximum (acute phase) and later declined by day 17-21. The tissue sections from infected animals during the establishment phase of infection indicated limited changes in surface epithelium with normal villous length. Although trophozoites of G. lamblia were seen in all sections lying free in the lumen as discrete parasite, the active invasion by the parasite could not be demonstrated. During the acute phase of infection, fuzzy appearance of brush border, marked reduction in villous height and infiltration of intraepithelial lymphocytes were commonly seen in all tissues. Electron microscopic observation demonstrated large numbers of trophozoites of G. lamblia preferentially aggregated at the base of the villi. At some sites, adhesive marks indicating attachment of Giardia trophozoites were also seen by scanning electron microscopy. In addition, severe flattening and blunting of microvilli and occasional loss of basic morphology of intracellular organelles of columnar cells were noticed at the site of parasite colonization under electron microscopy. The brush border microvilli were noted to be damaged in areas where parasites were attached to surface epithelium with the help of suction discs. The morphological changes associated with Giardia infection tended to reverse as the parasite load declined by day 17-21. Thus we feel that malabsorption in giardiasis with total or varying degrees of morphological alterations of surface mucosa can be explained on the basis of reduced absorptive surface area.