Giardia Life Cycle


Giardia is a single-celled parasite that causes diarrheal disease known as Giardiasis. This parasite falls under the order Diplomonadida. Diplomonads include small flagellates that reside in digestive systems of various animals like cats, dogs, termites, rats and then eventually humans. Giardia is found on the surface of soil, mud, or contaminated water debris from infected humans and animals.

Giardia has a simple life cycle which comprises two stages – the trophozoite and the cyst. Let’s look at the life cycle of Giardia to understand better.

Life Cycle of Giardia:

1) The Cyst – Stage 1 –

The cyst is hard, rigid and can survive any cold weather. They are resistant forms and are carriers of the disease Giardiasis. This infection occurs when contaminated water, food or fecal matter is ingested by human beings.

Excystation is the stage in which the parasite escapes from the cyst and emerges as a trophozoite. In the small intestine, the process of excystation begins where each cyst releases two trophozoites. These trophozoites multiply through binary fission, remaining in the small bowel.

2) The Trophozoite – Stage 2 –

Encystation is the process of forming a cyst or to become enclosed in a capsule. Encystation occurs when the parasite migrates to the colon. The cyst stage is most commonly found in non diarrheal feces. Owing to the infectious nature of cysts, shortly after passing stool, it can spread from one person to another.


In human beings with proper immune systems, the symptoms of Giardiasis may last around two to six weeks. This parasite causes the disease giardiasis. The symptoms of giardiasis can range from zero to chronic diarrhea. Giardia was initially called Cercomonas intestinalis in 1859 by Lambl and later renamed Giardia in 1915 by Stiles.

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Frequently Asked Questions on giardia-life-cycle


Where is Giardia most commonly found?

Giardia is a water-borne parasite that is most commonly found in swimming pools, water supplies, lakes, ponds and wells.


What does Giardia feces look like?

Since this parasite causes chronic diarrhea, the feces excreted is greasy, watery and has a foul smell. Bloating and loss of appetite are some other changes caused by giardia.


How long can giardia parasites survive on surfaces?

Given the appropriate circumstances, a giardia parasite can survive up to 7 days on a surface.


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