Giardiasis is a single-celled parasite that lives in a dog’s intestine. It infects older dogs but more frequently infects puppies.


Dogs become infected when they swallow water or other substances that have been soiled with faeces contaminated with Giardia. It can also be transmitted by eating or sniffing contaminated ground or by drinking contaminated water.


Microscopic parasites attach themselves to the intestinal wall and the damage causes a sudden onset of foul-smelling diarrhoea. The stool may range from soft to watery, often has a greenish tinge to it, and occasionally contains blood. Infected dogs tend to have excess mucus in the faeces. Vomiting may occur in some cases. The signs may persist for several weeks and gradual weight loss may become apparent.

The diarrhoea may be intermittent. Most dogs do not have a fever but may be less active. The disease is not usually life threatening unless the dog’s immune system is immature or immuno-compromised (in puppies and debilitated adult dogs, it may cause severe, watery diarrhoea that could be fatal if left untreated).