Giardia Lamblia - Symptoms, Transmission and Treatment

The Giardia lamblia, also called Giardia intestinalis or Giardia duodenale, is a protozoan parasite that the intestines of humans, causing diarrhea and abdominal pain.

The disease caused by Giardia lamblia is called giardiasis or giardiosis, and its transmission occurs through contact with feces of contaminated persons.

Giardia lamblia
Giardia lamblia

Giardia lamblia life cycle

Giardia has two morphological forms: cysts and trophozoites.

Cysts are the forms of the parasite released by the feces of infected patients, and may survive in the environment for a long time if there is moisture.

Giardia's transmission is fecal-oral, that is, it is caused by ingestion of Giardia cysts that emerge in the feces of humans or other mammals. The worse the sanitation conditions of a place, the greater the risk of epidemics of giardiasis. I will specifically talk about the broadcast media below.

After ingestion of the cyst, Giardia, in the small intestine, is transformed into the trophozoite form, becoming flagellate organisms that measure only 15 micrometers (0.015 millimeters). For a better understanding, we can say that the cysts function as eggs and the trophozoites are the puppies that leave the same. Trophozoites are the way to reproduce, multiplying inside the small intestine of the infected patient, sticking to your wall and feeding on food that passes.

When the parasite reaches the large intestine, it returns to the cyst form, as this is the only means of surviving the environment after its elimination in the feces.


As already mentioned, giardiasis is transmitted via the fecal-oral route. Any situation in which the Giardia cysts released into the stool reach the mouths of other people will cause the contamination. Some examples:
  • Drink or bathe in contaminated water.
  • Contamination of food by poorly washed hands. The cooking process kills Giardia's cysts, so this mode of transmission is more common with raw or contaminated foods only after they are ready.
  • Creches and institutions of the elderly where there is little concern with hygiene.
  • Anal sex.
  • Contact with feces of contaminated dogs and cats.
  • Handling of contaminated soil without proper cleaning of the hands.


Most people infected with Giardia lamblia will not have symptoms. In those who will have symptoms, the most common are:
  • Diarrhea, usually well liquid, but sometimes greasy, called steatorrhea
  • Abdominal cramps
  • Malaise
  • Flatulence
  • Nausea and vomiting
  • Weight loss

Fever is a less common symptom and occurs in less than 15% of cases.

The symptoms described above usually appear approximately 1 to 2 weeks after contamination with the Giardia cysts, lasting on average for 2 to 4 weeks.

After an acute phase, about 2/3 of the patients who have had symptoms spontaneously improve. 1/3, however, develop chronic infection by Giardia, remaining infected and symptomatic for long periods. In chronic giardiasis, the most common symptoms are:
  • Paste faeces
  • Steatorrhea (fatty stools and strong odor)
  • Significant weight loss
  • Tiredness
  • Depression

One of the main problems of Giardia infection is malabsorption syndrome, characterized clinically by weight loss and steatorrhea. The patient with giardiasis has difficulty digesting fats, carbohydrates and vitamins. Up to 40% of patients develop lactose intolerance.


Giardia infection is usually diagnosed through parasitological examination of faeces. As the parasite is eliminated intermittently, collection of at least three stool samples increases the chance of finding cysts.


Treatment of Giardia infection has two goals: to eliminate the symptoms in symptomatic patients and to stop the elimination of the cysts from the feces, breaking the chain of transmission.

Treatment can be done with the following drugs (adult doses):
  • Tinidazole (Pletil) 2000 mg single dose
  • Secnidazole (Secnidal) 2000 mg single dose
  • Metronidazole (Flagyl) 500 mg - 2 times a day for 5 days
  • Nitazoxanide (Annita) 500 mg - 2 times daily for 3 days
  • Albendazole (Zolben, Zentel) 400 mg - 1 time per day for 5 days
  • Mebendazole (Pantelmin) 300 mg - 3 times daily for 5 days

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