CYTOCHEMICAL STUDIES OF GIARDIA DUODENALIS

Giardiasis is a common waterbone intestinal disease and is caused by the
flagellated protozoan Giardia lambia. The trophozoite, or motile stage,
attaches to the microvillus border of the host intestinal epithelium by an
attachment organelle called the ventral disc. The attachment of the
trophozoite to the intestinal epithelium has been suggested to lead to the
symptoms of giardiasis which include diarrhea and malabsorption. Recent
evidence shows that the specific activity of enzymes found on the apical
surface of the intestinal cells in experimental animals and man is reduced
when trophozoites are present. The organism is transmitted via a cyst
stage. After ingestion of the cyst the organism actively leaves the cyst
to establish a new infection. The purpose of the studies proposed here are
to elucidate the mechanism of trophozoite attachment, study lysosome-like
vacuoles of the trophozoite which may affect the host epithelium and to
determine the mechanism of excystation. The specific objectives of this
proposal are: 1) to investigate the cytoskeleton of the attachment
organelle by detection of actin filaments by TEM, 2) to investigate the
cytochemical localization of lysosomal enzymes in the trophozoite at the
fine structural level, 3) to determine the ability of the trophozoite to
sequester foreign substances, including host glycoprotein, 4) to determine
the mechanism of excystation by cytochemical localization of acid
hydrolases, immunocytochemical localization of contractile protecins, and
in vitro excystation with use of inhibiting agents of lysosomes and
constractile protein.