Background. Giardiasis is a major diarrheal disease found throughout the world. This disease is caused by flagellate protozoan Giardia intestinalis (previously known as G. lamblia or G. duodenalis). G. lambliais the most common protozoal intestinal parasite isolated worldwide. Infection is more common in children than in adults. G. lamblia has two nuclei and eight flagella. The parasite attaches to human intestinal mucosa with a sucking organ.
Life cycle. The life cycle consists of two stages, the trophozoite, and cyst. The trophozoite is 9-12 μm long and 5-15 μm wide anteriorly. It is bilaterally symmetrical, pear-shaped with two nuclei (large central karyosome), four pairs of flagella, two axonemes, and a suction disc with which it attaches to the intestinal wall. The oval cyst is 8-12 μm long and 7-10 μm wide, thick-walled with four nucleus and several internal fibera. Each cyst gives rise to two trophozoites during excystation in the intestinal tract. Transmission is by ingestion of the infective cyst. The parasite is passed directly from the stools of infected people or animals to persons who ingest infected water, food, or other material.
Pathophysiology. G. intestinalis can cause asymptomatic colonization or acute or chronic diarrheal illness. The organism has been found in as many as 80% of raw water supplies from lakes, streams, and ponds and in as many as 15% of filtered water samples. It is a common cause of chronic diarrhea and growth retardation in children in developing countries.
Epidemiology. Giardia species are endemic in areas of the world that have poor sanitation. In developing countries, the disease is an important cause of morbidity. Water-borne and food-borne outbreaks are common. The organism has been found in as many as 80% of raw water supplies from lakes, streams, and ponds and in as many as 15% of filtered water samples. G. intestinalis is a particularly significant pathogen for people with malnutrition, immunodeficiencies, or cystic fibrosis. High-risk groups for giardiasis include travelers to highly endemic areas, immunocompromised individuals, and certain sexually active homosexual men.
Diagnosis. The traditional basis of diagnosis is an identification of G. intestinalis trophozoites or cysts in the stool of infected patients. Stool antigen enzyme-linked immunosorbent assays also are available.
Treatment. Standard treatment for giardiasis consists of antibiotic therapy. Metronidazole is the most commonly prescribed antibiotic for this condition.
References:
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Paniker, C.K.J. Paniker’s Textbook of Medical Parasitology 8thedition. [Revised and Edited by Ghosh, S]. Jaypee Brothers Medical Publisher (P) Ltd., India: 2018.
Curley, R., The Editors of Encyclopaedia Britannica. Available from: https://www.britannica.com/science/Giardia-lamblia#ref4490
