Giardia lamblia and Giardiasis

The Common Waterborne Parasite that Causes Beaver Fever

Jul 31, 2007

Giardia lamblia contaminates surface water all over the world and can cause an unpleasant prolonged intestinal illness known as giardiasis, or beaver fever.

Giardia lamblia is a protozoan, a single-celled parasite that lives in the intestines of people and animals. For the lucky, its presence causes no symptoms. For the less fortunate, G. lamblia causes an intestinal parasitic disease—giardiasis—that is always unpleasant, and may be prolonged.

How do you catch giardiasis?

Giardia lamblia is found in feces and in contaminated water supplies. People ingest the infective cysts of the parasite when they drink contaminated water or accidentally ingest fecal material on contaminated food items, hands, or other objects.

Giardia lamblia is resistant to chlorination and can survive water treatment. Unfiltered water supplies, particularly those drawn from surface supplies, have often been the source of outbreaks of giardiasis. Many animals can carry the parasite, including cats, dogs, sheep, cattle, muskrats and beavers (the source of the common name “beaver fever”). Infected people can cause an outbreak as well: contaminated hands can spread the parasite to food or objects.

What does Giardia lamblia look like and how does it live?

Giardia lamblia is much larger than bacteria, but still too small to be seen without a microscope. There are two stages, called cysts and trophozoites. Cysts are oval—watermelon shaped—and contain two pairs of nuclei that look like spherical eyes, along with a collection of other thread-like structures. Trophozoites are shaped like teardrops, with a broad rounded end and a pointy end that tapers off. The parasite alternates between the two stages:

The cyst stage is very resilient; it survives well in cool damp conditions and even in very cold water in winter. This is the stage that people swallow.
In the small intestine, the cyst breaks down, releasing two trophozoites, which attach to the intestinal lining and divide to produce more trophozoites.
Some trophozoites are carried away in the intestinal flow, especially when the host has diarrhea. As they move through the intestine, some secrete a resistant wall and become cysts.
Trophozoites and cysts of Giardia lamblia are passed in the stool. The trophozoites die quickly, but the cysts survive a long time in the right conditions.
Cysts are swallowed by another unsuspecting host and the process begins all over again.

What are the symptoms of giardiasis?

Many people have no symptoms, but some people become very ill and have trouble getting rid of this parasitic disease. Symptoms include:

Abdominal pain.
Watery diarrhea.
Foul smelling gas and burping.
Mild fever, sometimes with chills.
Malabsorption, where nutrients are not absorbed, frequently with weight loss.
In chronic infection, intermittent diarrhea alternating with normal stools and sometimes even constipation.

Avoid Giardia lamblia

It’s probably impossible to completely avoid coming in contact with Giardia lamblia, but you can lessen your chances of catching it:

Never drink untreated water from surface sources—rivers, streams, lakes. Treat water with filtration or a chemical treatment that kills protozoa.
When traveling in countries where sanitation is poor, drink bottled water and avoid uncooked vegetables that you do not peel yourself (with clean hands).
Practice good hygiene at all times: wash hands thoroughly after using the toilet and before handling food.

If you do catch giardiasis, take heart: you are not the first—Giardia lamblia cysts have been recovered from preserved human stools that are over two thousand years old. Two thousand years ago, this parasitic disease would have run its course, but today there are drugs that are usually very effective at killing the parasite.

Sources:

Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.

Foundations of Parasitology 6th Ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.

The copyright of the article Giardia lamblia and Giardiasis in Human Infections is owned by Rosemary Drisdelle. Permission to republish Giardia lamblia and Giardiasis must be granted by the author in writing.