Giardia lamblia (Giardiasis) : Habitat, Lifecycle,Clinical Manifestations, Laboratory Diagnosis , Treatment, Prevention and Control

Author : Roshni Nepal

Phylum – Sacrcomastigophora

Sub – phylum – Mastigophora

Class – Flagellata

Genus – Giardia

Species – lamblia

Giardiasis is an infection of small intestine, caused by a microscopic parasite called Giardia lamblia (upto 20µm). Giardiasis spreads through contact with infected people, through ingestion of parasitic cyst in contaminated water and food. Cysts are instantly infectious once they leave the host through feces (poop). An infected person might shed 1-10 billion cysts daily in their feces (poop) and this might last for several months. Pet dogs and cats also frequently contract giardia. They reside in the upper small intestine of host body.

Habitat and geographical distribution

G. lamblia inhabits duodenum and the upper part of jejunum of man. Giardiasis can be found all over the world. However, it’s more common in overcrowded developing countries that lack sanitary conditions and water quality control.

Life cycle of G. lamblia

Cysts are resistant forms that are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces. 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 occurs, which releases trophozoites (each cyst produces two trophozoites). Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small intestine, where they can be free or attached to the mucosa by a ventral sucking disk. Encystation occurs as the parasites moves toward the colon (large intestine). 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-to-person transmission is possible.

Fig – Life cycle of G. lamblia

Clinical manifestation of amoebiasis

After (1-3) weeks of incubation, first symptom of infection can be seen. In some cases, people infected with Giardia have no symptoms.

Acute symptoms include

  • Diarrhea
  • Gas
  • Greasy stools that tend to float
  • Stomach or abdominal cramps
  • Upset stomach or nausea/vomiting
  • Dehydration (loss of fluids)

Other, less common symptoms include itchy skin, hives, and swelling of the eye and joints. Sometimes, the symptoms of giardiasis might seem to resolve, only to come back again after several days or weeks. Giardiasis can cause weight loss and failure to absorb fat, lactose, vitamin A and vitamin B12. In children, severe giardiasis might delay physical and mental growth, slow development, and cause malnutrition.

Laboratory diagnosis

i. Macroscopy – appearance of stool in case of giardiasis is formed, with presence of mucus and blood.

ii. microscopy- detection of cyst and trophozoite in stool sample. Because Giardia cysts can be excreted intermittently, multiple stool collections (i.e., three stool specimens collected on separate days) increase test sensitivity

iii. ELISA, IHA, IFA (antibody detection using serum)

Treatment, prevention and control

  • Usually infection resolves in its own. But in case illness persists acutely, metronidazole, tinidazole or ornidazole can be used.
  • hand-washing and avoiding potentially contaminated food and untreated water
  • Boiling water contaminated with Giardia effectively kills infectious cysts; chemical disinfectants like iodine-based disinfectants can be used.

Binod G C

I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.

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