this ppt will helpful for a quick review in parasitology for medical students

1. Allen Rojer
AB Psychology, Study For MD

2. Morphology
• G. lamblia has two morphological stages:
the trophozoite and the cyst.

3. Trophozoites: Present in the small intestine, replicative formsCyst: 4 nuclei, cell wall; protects parasite from hypotonic lysis

4. Morphology - Trophozoite
• The trophozoite is pear shaped, with a broad anterior and
much attenuated posterior.
• It is 10-12µm long and 5-7µm wide, bilaterally symmetrical,
and has two nuclei.
• It is also relatively flattened, with a large sucking disk on
the anterior ventral side, which serves as the parasite’s
method of attachment to the mucosa of the host.
• The trophozoite also has two median bodies and four pairs
of flagella.

5. Morphology - Cyst
• It is the infective stage of parasite.
• A fully mature cyst is oval or ellipsoidal in shape and measures 8-12µm in
length and 7-10µm in breadth.
• Cyst is surrounded by a thick cyst wall. Cytoplasm is granulated and is
separated from the cyst wall by clear space.
• The axostyle lies more or less diagonally.
• A cyst contains 4 nuclei.
• The remaining of flagella and the margins of sucking disc may be seen
inside the cytoplasm.

6. Life Cycle
Life cycle of G. lamblia is simple and
completes in a single host, man.
No intermediate host is required.

8. • Infection is acquired orally by ingestion of cyst from contaminated hand
or water or food.
• Excystation occurs in the stomach and in the duodenum in the presence
of gastric acid, pancreatic enzymes (chymotrypsin and trypsin).
• Each cyst excysts to produce two trophozoites in the duodenum within 30
minutes of ingestion.
• These trophozoites multiplies in the intestine by bunary fission. Then they
adhere to enterocytes through their ventral sucker.

9. • Some of the trophozoites then pass down on the large intestine where they
again encyst in the presence of neutral pH and bile salts.
• The process of encystation begins with the appearance of encystation
specific secretory vesicles (ESVs) in the cytoplasm of trophozoites,
followed by production of cyst wall within 15 hours.
• Within 24 hours after appearance of ESVs, the trophozoite is covered with
these cyst wall proteins, resulting in formation of cyst.

10. • Formation of cyst begins by shortening of flagella followed by
condensation of cytoplasm and finally secretion of thick hyaline cyst wall.
• These encysted trophozoites then undergo another phase of nuclear
division and produces quadrinucleated(4) mature cyst.
• The cysts which are the infective form of parasite are excreted in faeces
and life cycle is repeated.

11. Diagnosis
• Diagnosis is made by finding trophozoites or cysts or both in diarrheal stools.
• In formed stools (e.g., in asymptomatic carriers), only cysts are seen.
• An enzyme-linked immunosorbent assay (ELISA) test that detects Giardia antigen in
the stool is also very useful. Tests for antibody in the serum are not routinely
available.
• If those tests are negative and symptoms persist, the string test, which consists of
swallowing a weighted piece of string until it reaches the duodenum, may be useful.
• The trophozoites adhere to the string and can be visualized after withdrawal of the
string.

15. Treatment
The treatment of choice is Metronidazole (Flagyl) or
Quinacrine hydrochloride.

16. • Quinacrine has been used as an
antimalarial drug and as an
antibiotic. It is used to
treat giardiasis
• Metronidazole is
an antibiotic that needs to be
taken for five to seven days. It can
cause nausea and leave a
metallic taste in your mouth.

18. Prevention
• Prevention involves drinking boiled, filtered, or iodine-treated water in endemic
areas and while hiking..
• Proper disposal of human feces.
• Maintenance of good and proper personal hygiene.
• Health education at individual as well as community levels.
• No prophylactic drug or vaccine is available.