Giardia are protozoans, tiny, one-celled parasitic life forms with the potential to cause serious illness. Some dogs are carriers who show no symptoms, but others get sick and need treatment. Like many disease organisms, Giardia mature in stages. Unlike many others, no time elapses between infestation with the dormant phase and activation of the disease. The cysts (the inactive form) are found in contaminated water and feces.
Once ingested by the dog, the cysts open and discharge the mobile form known as the trophozoite, a pear-shaped critter with whip-like flagella that propel it through the intestine. If the dog is healthy, the trophozoites may live in the lower digestive tract for years. If the dog has an immature or overburdened immune system, the trophozoites continue to multiply by dividing and can cause the debilitating disease. Cysts can remain viable for several weeks or months in cold, wet environments.
