Parasites In Humans
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Giardia Intestinalis

Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis) is a protozoan flagellate causing giardiasis in the small intestine. It attaches to the mucosa and absorbs nutrients that it gets from the intestinal wall. In addition to humans, Giardia intestinalis infects birds, cows, sheep, deer, dogs and cats. Giardiasis is found worldwide mostly in warm climates.

Giardia intestinalis lives as active trophozoites in the small intestine. Some trophozoites encyst into cysts which are released in a bowel movement. The feces might contaminate soil, water, food or surfaces such as bathroom sinks. The cyst has a protective shell and it can survive in the environment for many weeks (in cold water many months). You become infected after accidentally swallowing the microscopic cysts. Each cyst releases two trophozoites in the small intestine. They remain in the lumen where they can feed freely or attached to the mucosa by a ventral sucking disk. After eating enough, they go through another transformation and multiply by binary fission. The trophozoites encyst as they move towards the colon. Cysts are found more often in firm stool whereas both trophozoites and cysts are present in loose stool. Because the cysts become infective almost instantly after being passed out, the disease can be transmitted during anal-oral-sexual intercourse.

Giardia intestinalis life cycle

Common giardiasis symptoms include:

  • bloating
  • bad breath and farts
  • dehydration
  • diarrhea or greasy floating stools
  • fatigue
  • loss of appetite
  • nausea
  • stomach ache
  • weakness
  • weight loss.

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.

Giardia intestinalis

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.

Your health care provider makes the giardiasis diagnosis by examining stool samples under a microscope. Common microscopical techniques include: wet mount with iodine, trichrome or immunofluorescent 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.

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

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