Giardia is a parasite found in the intestines of humans and most types of domesticated animals throughout the world, including cats. It is also a common cause of diarrhea in cats, especially among cats in catteries and group housing situations.
However, healthy animals rarely will experience diarrhea or other symptoms unless they are exposed to an unusually high number of Giardia. Young kittens and debilitated older cats, both of which have weaker immune systems, are much more likely to show symptoms from moderate numbers of the parasite.
Protozoan organisms, Giardia appear in two forms: as a swimming trophozoite, or feeding form, and as a cyst that contains the swimming trophozoites. The cysts, and not the trophozoites, are transmitted from one cat to another when an animal becomes infected.
