Giardia is a tiny organism, called a protozoa, made of only one cell! For such a tiny creature, it is amazing the trouble giardia can cause, but it can make affected cats quite poorly. Although any cat can be affected with giardia, it is more likely in young cats, as their immune systems are not as strong and less likely to be able to fight off a giardia infection.
Giardia reproduce in the intestines by producing special infectious cysts which are released into the environment in faeces. Cats who ingest these cysts are then infected themselves. Giardia can infect many animals as well as cats, including dogs, ferrets and humans.
Giardia can be difficult to diagnose, as cats which are affected often only have giardia in their faeces intermittently and may show no signs of infection. This means that a test can be negative, even if giardia are actually present – repeated tests may be needed to track this little parasite down!