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Giardiasis Definition

Giardiasis is an infectious disease that occurs in the small intestine. Giardia is a tiny microscopic parasitic organism that leads to this diarrheal sickness. This parasite is often found in contaminated water, food and faecal matter of already infected animals or people. This parasite is protected by an outer shell like covering and can stay alive outside the human body for a prolonged period of time. The most common way in which this disease spreads is by contact with contaminated water (drinking or swimming), food exposed to manure or washed in agricultural runoff, handling diapers, living in squalid conditions and unprotected sex.

Giardiasis Symptoms

Symptoms can vary a lot amongst those infected by Giardiasis. While some people do not display any symptoms, they may end up releasing cysts through stool and thereby pass the disease to others. Other people may develop chronic or diarrheal sickness within one to two weeks of contracting the infection. Small children are particularly susceptible to this infection. Some common symptoms are:

  • Diarrhoea with large amount of watery stool initially, gradually turning greasy and foul smelling
  • Weight and appetite loss
  • Failure to absorb fat, digest milk and vitamins (A & B)
  • Abdominal cramps, vomiting
  • Headaches & Nausea
  • Constipation & Gas

Small children are particularly susceptible to this infection as severe cases of Giardiasis infection can lead to slower physical and brain development and can lead to malnutrition.

Giardiasis Risk Factors

This parasite is protected by a tough outer cyst and can stay alive outside the human body for prolonged period of time – they are also infectious once they leave the host body. While an infected person can shed up to 10 billion cysts each day, it takes less than 10 cysts to make someone infected. Even strong chemicals like chlorine have no effect on it. The infection rates typically go up during summers.

The most common risk factors for contracting this disease are:

  • Drinking untreated or contaminated water
  • Swallowing water during recreational activities (swimming pool)
  • Eating food exposed to manure or washed in agricultural water
  • People handling diapers and faecal matter
  • Living in squalid and cramped conditions
  • Unprotected oral or anal sex

Giardiasis Diagnosis

Routing ova and parasite examination through analysis of fecal discharge is a common method used to identify Giardia. The most effective method is a routine antigen testing of the stool. Since the cysts are excreted intermittently, it is important that several stool collections are made on separate days. Also, the variability of concentration of cysts makes the diagnosis of this infection difficult. More sensitive fecal immunoassays are effective in such cases. In some cases, molecular testing is used to identify various subtypes of this parasite.

Other methods include String testing wherein a string is inserted into the duodenum to get a sample of duodenal fluid. This fluid laced string is then observed under a microscope. It is a relatively painless procedure. More invasive methods may include biopsy of the small intestine.

Giardiasis Treatment

In patients having Giardia infection without symptoms, no treatment is usually prescribed as the infection clears out on its own in a few weeks. In case there is a risk of infection spreading to other patients, several drugs are available to treat the infection.

Pregnant women are treated differently as there is potential risk of adverse side effects of the drugs on the unborn fetus. Their primary doctor is best suited to guide them post the first trimester.


The most popular one is the antibiotic Metronidazole. The common side effects encountered is a metallic taste in the mouth. It is advisable to not consume alcohol during this treatment.

The antibiotic Nitazoxanide comes in a liquid form and is easier to swallow by children. Some common side effects include flatulence, yellow eyes and bright yellow urine.

UPDATED ON 14/05/2024

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