Travel Medicine

Emerging Infectious Diseases and Other Conditions

Giardiasis

What is giardiasis?

Giardiasis is an infectious diarrheal disease caused by the parasite Giardia lamblia, which can be transmitted through oral-fecal contact and by water contaminated by feces. Travelers are cautioned against drinking any untreated water.

According to the National Institute for Allergy and Infectious Diseases (NIAID), Giardia lamblia is one of the most common intestinal parasites in the world. It causes infection up to 20 percent of the world's population, and is most prevalent in developing countries, where infections are associated with poor sanitary conditions, poor water quality control, and overcrowding.

According to NIAID, Giardia is a major cause of waterborne outbreaks of diarrhea in the United States. It occurs primarily in areas where water supplies have become contaminated with feces from humans or, possibly, from animals. Outbreaks have occurred throughout the country.

What causes giardiasis?

The Giardia lamblia parasite lives in two stages:

trophozoites - the active form inside the body.
cysts - the resting stage that enables the parasite to survive outside the body.

Infection begins when the cysts are consumed through food or water. Stomach acid activates the cysts and the trophozoites are released. They become attached to the lining of the small intestine and reproduce. Cysts form in the lower intestines and are then passed in the feces.

The parasite may be directly transmitted from person to person by contact with infected feces, or indirectly, through consuming food and water contaminated with cyst-containing feces.

What are symptoms of giardiasis?

The time between infection and the onset of acute symptoms usually is from one to two weeks. Some infected people have very mild symptoms or no symptoms at all, or may experience:

a sudden explosive, watery, foul-smelling diarrhea
excessive gas
abdominal pain
bloating
nausea
tiredness
loss of appetite

The illness may last for months or years, causing recurrent mild or moderate symptoms such as:

impaired digestion, such as lactose intolerance
intermittent diarrhea
tiredness and weakness
significant weight loss

How can giardiasis be prevented?

Giardiasis cannot be prevented, but the spread of it can be contained by practicing good personal hygiene, as well as proper hygiene when caring for those who may be infected with the parasite. When visiting in an area where giardiasis is known to exist:

drink only boiled water or bottled carbonated water or drinks
avoid ice and beverages made from tap water
do not eat locally-grown uncooked or unpeeled fruits and vegetables

How is giardiasis diagnosed?

Positive diagnosis of giardiasis is made by microscopic identification of the parasite.

How may giardiasis be treated?

Giardiasis may be treated with medications prescribed by a physician. Specific treatment for giardiasis will be determined by your physician(s) based on:

your overall health and medical history
extent of the disease
your tolerance for specific medications, procedures, or therapies
expectations for the course of the disease
your opinion or preference

This page was last updated on: February 14, 2008.

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