Giardia intestinalis (lamblia) is the most common intestinal parasite found in humans in the United States.

Giardia lamblia/CDC
Giardia lamblia/CDC

Giardia is a protozoan parasite that lives in the intestine of infected humans and animals (in particular, beavers and domestics animals like cats and dogs). It is found in the environment on surfaces (where it can survive for long periods), water and food that has been contaminated with the feces from an infected person or animal.

Children are more commonly infected than adults. The following have been implicated in both small and large community outbreaks:

Giardia is a particular problem in areas where children are not toilet-trained, likeday care centers. In these cases, toys and other things the children touch may become contaminated with feces (even if it’s not visible). The next child plays with the toys and puts his finger in his mouth and so on and so on.

Giardia is also an issue in recreational water like swimming pools, water parks, lakes and streams. In places where young children swim and may defecate in the water.

Hikers and campers can be at risk of infection if they drink stream or lake water that may be contaminated with infected human or animal feces.

Drinking water, using ice made from contaminated water and eating fruits and vegetables washed in contaminated water are all common ways to get infected with the parasite, particularly when traveling overseas.

Sometimes it is of concern with well water if the well is located at the bottom of a hill or is shallow, because of run-off and flood water contaminating the well. In addition, if the well water is in an area where animals graze and the animal waste contaminates the ground water. There are situations where testing for Giardia in well water is warranted.

Chlorination is generally ineffective in killing the Giardia parasite, so if you can’t avoid drinking potentially contaminated water, boil it or filter it with a filter that is rated for “cyst removal”.

There are also documented cases of the parasite being transmitted via sexual contact (anal-oral).

Most cases of Giardia, up to 50%, are asymptomatic. If you do get sick, the symptoms of Giardia usually start about a week after being infected. Symptoms can be divided between mild, acute and chronic infections.

Mild infection

This is typically moderate diarrhea followed by spontaneous recovery in 6 weeks.

Acute infection

This is characterized by sudden onset of explosive, foul-smelling, watery diarrhea without blood or pus, intestinal gas, abdominal cramps, nausea, excessive tiredness, bloating and chills. If left untreated, this can last for weeks or months.

Chronic infection

Chronic infection is often characterized by steatorrhea, greasy, frothy stools that float. This is due to the malabsorption of fats.

The diagnosis of Giardia is traditionally made by microscopic examination of stools to identify theparasite. Because of the way Giardia is shed, 3 negative stools are necessary to rule out the parasite.

There are also tests for detecting antigens in stool or special immunofluorescent techniques, which are generally more sensitive than microscopic examination.

Also visit and “like” the Infectious Disease News Facebook page HERE