Grr...going to the vet tonight for runny poo (3 weeks - there's a thread over in Health & nutrition). He'll be testing for Giardia. I've just read this - and am even angrier than usual at the amount of people that do not pick up dog poo where I walk. I will have to find a different walk - because I did not know a dog could get this just by SNIFFING another dog's poo (bold is mine): How do dogs get giardiasis? giardia_2009A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. In susceptible dogs, once the cyst passes into the dog's intestines; it goes through transformation to the trophozoite or feeding form and attaches to the intestinal wall to feed. If sufficient numbers are present, clinical signs of damage to the intestinal wall will develop. Trophozoites reproduce by dividing, and some transform into the cystic form. Eventually, the dog passes cysts in its stool. "Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water." These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water. When Giardia cysts are found in the stool of a healthy adult dog without diarrhea, they are generally considered a transient, insignificant finding. However, in puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal if left untreated. The likelihood of developing disease increases when large numbers of cysts are present in the environment from fecal contamination. Giardiasis is a common occurrence in environments that are densely populated, such as kennels, pet stores, or animal shelters. GRRR!