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Giardia lamblia


Giardia lamblia, also known as Giardia intestinalis, Giardia duodenalis, Lamblia duodenalis or Lamblia intestinalis, is a flagellated protozoan parasite that specifically infects the small intestines of its host. It has a distinct characteristic of resembling an 'old man with eyeglasses' or a 'monkey face'.

It was first observed by Anton Van Leeuwenhoek in his own stools when he was suffering from diarrhea in 1681.

Appearance of a Giardia lamblia cyst and trophozoite.

Appearance of a Giardia lamblia cyst and trophozoite.


Having the knowledge on what G. lamblia looks like is essential for its diagnosis. There are two stages that can be found in the stool infected by the parasite:

  1. Cyst - can be found in the stool with formed consistency. It is necessary to have precautions when handling stools since this is the infective stage of the parasite.
  2. Trophozoite - can be found in the stool with watery consistency. Its motility can also serve as a diagnosis tool for the parasite.

The cyst is of oval or ellipsoidal in shape and has the size of 8-19 um. In stained smears, a 'halo effect' can be noted around the outer part of the cyst's wall.

Trophozoites, on the other hand, is a pear-shaped parasite measuring 10-20 um. When examined in a wet-mount slide, its 'falling leaf' motility can be demonstrated. It has two sucking disks in its ventral surface, constituting the 'old man with eyeglasses' appearance.

Life Cycle

The infection caused by G. lamblia starts in the ingestion of food contaminated of its cysts by the host. Cysts undergo excystation (exits the cyst stage) becoming trophozoites. The trophozoites will reproduce asexually through binary fission in the intestine. Some of these trophozoites undergo encystation (entering the cyst stage) before reaching the rectum. Both trophozoites and cysts are passed out in the feces but due to its motility, only cyst can survive in the environmental change and can live weeks up to months in cold water.

The life cycle of Giardia lamblia.

The life cycle of Giardia lamblia.

Pathogenesis and Clinical Manifestations

Giardiasis or lambliasis is the disease caused by the parasite G. lamblia.

G. lamblia uses its two sucking disks to facilitate attachment in the intestinal cells which can cause intestinal irritation to the host. The parasite is able to avoid the host's immune system by attaching itself in the villi or within the intestinal mucus. This attachments can cause the alteration of substances absorption in the intestines leading to deficiencies.

In acute infections, symptoms include abdominal pain, cramps, diarrhea, excessive flatulence where the gas expelled resembles the smell of a 'rotten egg'. Other clinical manifestations include bloating, nausea, anorexia and malaise.

Chronic infections may demonstrate steatorrhea (fat malabsorption; presence of fats in feces) where stools float on toilet water. Other patients complain of alternation of diarrhea and constipation.


Examination of the patient's stool specimen is still the most utilized method in the diagnosis of giardiasis. Cysts are often found in formed feces while trophozoites are often demonstrated in watery specimens.

Duodenal aspiration specimens may also be used for diagnosis. The specimen can be obtained through gastroduodenoscopy or through nasogastric insertion. In this specimen, trophozoites are expected to be examined.

String test is usually done if other laboratory methods can't demonstrate the presence of G. lamblia in a suspected host. The test is done by attaching a gelatin capsule at the end of a very long string. The capsule is swallowed by the patient while the other end of the string stays outside the patient's mouth, taped on his or her cheek. After four to six hours, the string is pulled by a health professional and examines the dissolved capsule for the presence of the parasite.

String test is also called Enterotest. Due to its difficult procedure and highly uncomfortable to the patient, the test is now slowly being replaced by endoscopy.

String test or Enterotest for the diagnosis of giardiasis.

String test or Enterotest for the diagnosis of giardiasis.

Treatment and Prevention

There are four drugs often used for human infection: metronidazole, tinidazole, nitazoxanide and albendazole. Metronidazole is the first drug utilized when diagnosed of giardiasis. However, this drug is not advised for pregnant patients since it is mutagenic and carcinogenic in bacteria and mice respectively. These four drugs have different duration of use and side effects when taken.

G. lamblia is most often transmitted through contaminated water. Boiling the water used for drinking for at least five minutes is the best way to prevent infection from the said parasite. Better sanitation in food preparation and organized sewage system can also minimize the giardiasis.

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