Giardia is a protozoan parasite that can be transmitted to humans via drinking water that is contaminated with feces. The prototypical species is Giardia lamblia. The protozoan causes an intestinal malady, typified by diarrhea that is called giardiasis. The intestinal upset has also been dubbed "beaver fever."

The natural habitat of Giardia is the intestinal tract of warm-blooded animals. In the wild, warm-blooded creatures such as beavers and bears are natural reservoirs of the protozoan. Also, domestic dogs and cats can harbor the microbe. Typically, Giardia is passed onto humans by the fecal contamination of drinking water by these animals. The ingestion of only a few cysts is sufficient to establish an infection

Giardia has two distinct morphologies. In the environment, such as in water, Giardia is in the form of what is termed a cyst. An individual cyst is egg-shaped and contains four...