Parasites and Biliary stones

Giardiasis ٥٨
the alkaline, protease-rich juice of the proximal duodenum (Adam,
2001).
Excystation yields the release of 2 motile trophozoites,which
replicate by binary fission and principally inhabit the proximal small
intestine. The trophozoites do not invade the epithelium; instead, they
appear to adhere to the epithelial surface by suction with a ventral disk,
although the precise molecular mechanism by which this occurs is
unknown. Trophozoites encyst in the jejunum, in a process that is
triggered by a particular composition of biliary secretions. In vitro studies
have suggested that encystation is activated by deprivation of cholesterol
from the environment (Lujan et al., 1996).
Pathogenesis and pathology:
Excystation of ingested cysts occurs in the stomach and duodenum.
Released trophozoites reproduce by binary fission and in the small bowel
attached to the mucosal surface. G. lamblia in feces encysts and is passed
into the environment, continuing the cycle (Owen et al., 1979 and
Bingham and Meyer, 1979).
Acute and chronic diarrhea with weight loss and growth retardation
are the clinical presentations of symptomatic giardiasis. The mechanisms
through which G. lamblia causes disease are not known. Postulated
mechanisms include mechanical obstruction and interference in
absorption of fats and fat-soluble vitamins caused by trophozoite
attachment to the mucosa ,direct irritation of the mucosa by the sucking
disk (Owen et al., 1979 and Erlandsen and Chase, 1974), bacterial
overgrowth and bile salt deconjugation (Tandon et al., 1977). Osmotic
diarrhea from a parasite caused reduction in intestinal mucosal
disaccharidase (Hoskins et al., 1967) and production of an enterotoxin
(Meyer and Radulescu, 1979).