Study of Giardia – Classification and Life Cycle

Classification of Giardia

Phylum :- Protozoa
Subclass :- Sarcomastigophora
Class :- Zoomastigophorea
Order :- Diplomonadida
Genus :- Giardia

Study of Giardia - Classification and Life Cycle

Comments on Giardia

  • It is live in the intestine of man as an endoparasite and cause Giardiasis
  • It has two nuclei and bears four flagella on either side of the body
  • Its fee on vitamins and amino acids contained in food within the intestine.
  • Giardia intestinalis trophozoites are pear-shaped and 10–20 µm long.
  • Other characteristics include: flagella, median bodies, sucking disks and two big nuclei.
  • Giardia intestinalis cysts are oval to ellipsoid and 8–19 µm long
  • Immature cysts have two nuclei, whereas mature cysts have four.

Causal Agent :- Giardia intestinalis is a protozoan flagellate (Diplomonadida). This protozoan was initially named Cercomonas intestinalis by Lambl in 1859. It was renamed Giardia lamblia by Stiles in 1915 in honor of Professor A. Giard of Paris and Dr. F. Lambl of Prague. However, many consider the name, Giardia intestinalis, to be the correct name for this protozoan. The International Commission on Zoological Nomenclature is reviewing this issue.

Life Cycle of Giardia

Study of Giardia - Classification and Life Cycle

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages)

  • The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites)
  • In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites)
  • Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk.
  • Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in non-diarrheal feces.
  • Because the cysts are infectious when passed in the stool or shortly afterward, person-toperson transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear.


It inhibits the intestine of man and other vertebrates like rat, rabbit, dog, cat etc.


  • Bad breath and farts.
  • Dehydration.
  • Diarrhea or greasy floating stools.
  • Fatigue.
  • Loss of appetite.
  • Nausea & Stomach ache
  • Weakness

Diarrhea can be fatal, if you do not drink enough water with salt and glucose. Another not so recognizable effect is the lack of B12-vitamin. This is due to the impaired absorption (malabsorption) in the damaged intestinal wall. 50 % of giardiasis cases are asymptomatic. Symptoms begin usually within two weeks after becoming infected. In healthy individuals the sickness normally persists up to three weeks, but sometimes longer.


By examining stool samples under a microscope. Common microscopical techniques include: wet mount with iodine, trichrome or immune fluorescent antibody staining and/or enzyme immunoassays. Several stool samples are usually needed on different days because cysts and trophozoites are not always present in the feces. Trophozoites can also be found from duodenal fluid or from biopsies taken during endoscopy

Mode of Transmission

It occurs by ingestion of food or water containing protozoan cysts. It is transmitted by unprotected sexual intercourse.


It accomplished with antimicrobial drugs such as: metronidazole, nitazoxanide (good for treating children), tinidazole, paromomycin, quinacrine and furazolidone.


Prevention is achieved by protected sexual intercourse and good personal hygiene.

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