Although members of the eukaryotic domain of life, which is characterized by cells that contain membrane-bound organelles, giardia are one of a handful of eukaryotic genera that do not have mitochondria. This may or may not contribute to their vulnerability to UV light.
Normally, giardia exist as free cells in water. As is the case with many protists, when the environment becomes harsh, giardia cells can convert to a cyst form (oocysts). Oocysts are resistant to various water treatments including chlorination. When cysts are ingested, giardia can become parasites within humans, causing enteritis characterized by diarrhea and gas. Diagnosis can be confirmed with the detection of oocysts in stool samples.
During the first decade of the 21st century, studies revealed that UV radiation of certain wavelengths was useful in killing oocysts of both giardia and another parasitic protist known as cryptosporidium. In 2010, researchers at Tel Aviv University announced the development of a device that integrates into tap water systems, treating the water with the optimal anti-parasitic UV wavelength.