Giardiasis: What It Is, Causes, Symptoms & Treatment

Ann Schreiber

Ann Schreiber

Medically reviewed by Mark Arredondo, M.D.

Updated on September 06, 2023

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Giardiasis might sound unfamiliar. In the United States, only a small number of people, around 1 or 2 in 10,000, get infected with giardia yearly, according to Harvard Health. But if someone who has recently visited a developing country experiences ongoing diarrhea, the odds of having giardia rise to about 1 in 3.

This article will delve into this parasitic disease: what giardia is, what causes it, the symptoms it brings, and how it can be treated.

What is giardiasis?

“Giardiasis is a parasitic infection caused by the protozoan Giardia lamblia, affecting the digestive system. It is North America’s most common intestinal parasite and the third most common etiology of diarrheal disease in children under 5 years old worldwide,” said Dr. Alfredo Mena Lora, director of infectious diseases at Saint Anthony Hospital in Chicago.

Giardiasis causes

“You can get giardiasis by ingesting contaminated water or food that contains the giardia parasite,” Mena Lora said. "Transmission can occur in day care centers, outdoor recreation or swimming pools, and overcrowded areas with poor sanitation."

The U.S. Centers for Disease Control and Prevention says you can get infected when you ingest the giardia parasite, a microorganism. The parasite, often present in the feces of infected people or animals, can contaminate objects it comes into contact with. The ease of giardia transmission is remarkable -- even a small amount of fecal matter entering your mouth can lead to illness.

The spread of giardiasis can occur through:

  • Consuming contaminated food or water that contains giardia microorganisms.
  • Being near an individual with giardiasis, especially in environments like child care facilities.
  • Traveling in regions with poor sanitation practices.
  • Coming into contact with feces, even through sexual activity, from someone currently ill or recently recovered from giardiasis.
  • Accidentally transferring giardia microorganisms from contaminated surfaces (like restroom handles, changing tables, diaper bins or toys) to your mouth.
  • Contact with infected animals or environments tainted with fecal matter.

Giardiasis symptoms

Certain individuals with a giardia infection may not display any indications or symptoms, according to the Mayo Clinic. Nevertheless, they still harbor the parasite and can transmit it to others via their feces. In cases where individuals do fall ill, symptoms typically emerge within one to three weeks after exposure. They can include:

  • Loose, occasionally unpleasant-smelling diarrhea that might alternate with soft, oily stools
  • Weariness
  • Abdominal discomfort and bloating
  • Excessive gas
  • Sick feeling
  • Weight loss

Symptoms of giardia infection can last two to six weeks, though in some cases, they might last even longer or resurface.

Giardiasis treatments

“Luckily, we have great treatment options for giardiasis," Mena Lora said.

A doctor can prescribe oral antibiotics that can treat this infection easily and with a cure rate topping 90%, he said.

"The incubation period is one to two weeks," Mena Lora noted. "Giardiasis symptoms typically last two to six weeks but vary based on individual health and treatment. Most infections are self-limited.”

Various medications are available for managing giardia infection, according to the CDC. They include the antibiotic metronidazole; and two antiprotozoans, tinidazole and nitazoxanide. Additional medicines include paromomycin, quinacrine and furazolidone. Some of these medications are not available in the United States.

Living with giardiasis

Before treatment, people affected by giardiasis can experience relief from symptoms within two to six weeks, according to the CDC. Sometimes, however, symptoms might seem to vanish, only to resurface after a few days or weeks. On occasion, individuals with giardiasis might face enduring challenges, such as reactive arthritis, irritable bowel syndrome and recurrent diarrhea that could extend over several years.

This condition can be particularly troublesome for children, potentially causing setbacks in physical and mental growth developmental pace and leading to malnutrition.

"If you have bloating, diarrhea or other abdominal symptoms concerning giardiasis, seek medical advice, stay hydrated and practice good hygiene to prevent the spread of the infection,” Mena Lora said.

Addressing symptoms promptly, seeing a health care provider for treatment, staying hydrated and adopting proper hygiene measures are vital in managing giardiasis and minimizing its impact on daily life.


Alfredo Mena Lora, MD, director, infectious diseases, Saint Anthony Hospital, Chicago

Harvard Health: Giardiasis

U.S. Centers for Disease Control and Prevention: Parasites - Giardia

U.S. Centers for Disease Control and Prevention: Diagnosis and Treatment Information for Medical Professionals

U.S. Centers for Disease Control and Prevention: Giardia, Illness and Symptoms

Mayo Clinic: Giardia Infection (Giardiasis)

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