Malabsorption in giardiasis: presence of a luminal barrier (mucoid pseudomembrane). A scanning and transmission...

Investigations of the small bowel mucosa by scanning and transmission electron microscopy are reported in two coetaneous children with giardiasis. Serum immunoglobulins and mucosal architecture by light microscopy were normal in both, as well as activities of lactase, sucrase, and maltase. One of the children had suggestive evidence of malabsorption. Scanning and transmission electron microscopic examination of biopsied mucosa of the child with malabsorption suggested the following: increased secretory activity in crypts and increased cell damage, producing excess mucus containing extruded cytoplasm. It is hypothesized that the physicochemical properties of the mucoid material permitted ready interaction with the mucosal surface, the biochemical qualities of which could have been altered by the presence of the parasites. Close adherence of this mucoid layer to the surface gave it the aspect of a pseudomembrane which, by covering wide areas of the mucosal surface, probably functioned as an effective luminal barrier for nutrients. This pseudomembrane was not seen by light microscopy. Excessive secretion of mucus, its physicochemical and immunologic properties, and mucus-mucosal surface interaction could have been engendered by genetic and environmental factors, which need further study. Although some mucus was present in the mucosa of the other child, it was confined to the base of the villi, and did not cover the mucosal surface. The presence of a luminal barrier (mucoid pseudomembrane) may be added to the list of mechanisms implicated in causing malabsorption in giardiasis.