Disaccharidase deficiencies in Mongolian gerbils (Meriones unguiculatus) protected against Giardia lamblia.

The activities of the disaccharidases lactase, maltase, sucrase and trehalase were examined in gerbils during Giardia lamblia infections. In a primary infection with trophozoites, the activities of all four enzymes were reduced from day 10 post-infection (p.i.) and remained at low levels well past the elimination phase of the infection. However, during a challenge infection, the disaccharidase decreases were short-lived, with impairments being seen only on days 2 and/or 4 post-challenge (p.c.). Sucrase activity was not affected by a challenge infection. When 0.1 mg of a soluble extract of G. lamblia trophozoites was used to challenge gerbils previously exposed to the live parasite, the pattern and duration of enzyme deficiencies were comparable with those observed after the challenge with the live parasite. In addition, decreasing the extract dose used to challenge the gerbils led to smaller disaccharidase deficiencies. G. lamblia-infected gerbils were also challenged with a soluble extract of Entamoeba histolytica trophozoites, and this had no effect on the disaccharidase activities. Therefore, the presence of the intact parasite was not necessary to induce enzyme reductions in immune animals. In addition, the effects seen during the secondary infection were parasite-specific and may have involved the host's immune response to Giardia antigens. Immune gerbils were further challenged with the in vitro-released excretory/secretory products of G. lamblia. Under our experimental conditions, disaccharidase activities were found to be affected by these products in a manner that was inconsistent with the results of the live parasite challenge, and this merits further study.