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.
7.
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.
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.
17.
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.
Notes de l'éditeur
An axostyle is a sheet of microtubules found in certain microbial eukaryotes. It arises from the bases of the flagella, sometimes projecting beyond the end of the cell, and is often flexible or contractile, and so may be involved in movement and provides support for the cell.
escape from a cyst or envelope, as in that stage in the life cycle of parasites occurring after the cystic form has beenswallowed by the host.
A string test, also called an "entero-test," is one type of test used to detect the presence of parasites in the upper part of the small intestine. Once established, these parasites can grow and thrive at your expense.
To have this test, you swallow a string with a weighted gelatin capsule on the end. The string is pulled out 2- 4 hours later. Any bile, blood, or mucus attached to the string is examined under the microscope. This is done to look for cells and parasites or parasite eggs.