Infected cats tend to have excess mucus in the feces. Sometimes, vomiting can occur. Ingestion of the cyst stage of the parasite leads to infection. Once inside the cat's intestine, the cyst goes through several stages of maturation. Eventually, the cat is able to pass infective cysts in the stool, where they can contaminate the environment and infect other cats.
Infection can also occur from drinking water which has been contaminated with the cysts.
Because of the prevalence of Giardia in the cat, the presence of cysts in the stool does not necessarily indicate that a problem is present. When the cysts are present in a cat with diarrhea, it is important. In particular, kittens and debilitated adult cats are at risk for death from dehydration associated with the diarrhea . Although a fecal examination is needed for diagnosis, the routine flotation test may fail to detect these small cysts. A special solution may be needed for accurate identification of the cysts in the stool.