Dr. Andrew Peregrine, a veterinary parasitologist at the Ontario Veterinary College, presented some data about the types of Giardia found in dogs and cats in Ontario at this week’s University of Guelph Centre for Public Health and Zoonoses annual meeting.

A lot of attention has been paid to Giardia types in recent years. That’s because, contrary to earlier thoughts, it’s now known that certain types (also called assemblages) of Giardia can infect multiple species while others are host specific (i.e. they only infect one species). This is very important because if a dog or cat is shedding Giardia in their stool, the type determines whether there is any risk to people.

In the Ontario study, 75 canine and 13 feline Giardia-positive fecal samples were typed. In canine samples, assemblage D accounted for 68% of samples, while assemblage C accounted for 31%. These two are dog-specific, meaning 99% of typed canine samples contained only dog-specific types and were therefore no risk to human health. The other sample contained assemblage B, a zoonotic type that infects humans and animals. In contrast, 13/13 of the feline samples were assemblage A, a zoonotic type of Giardia.

These recent Ontario data indicate a low risk of transmission of Giardia from dogs to people, but some risk from cats – at least in Ontario. It’s important to note that there appears to be geographic variation in this trend. Other recent studies have reported similar results, with the predominance of dog-specific types in dogs. However, a few studies have shown a predominance of the zoonotic assemblage A in dogs. These have mainly been in low socioeconomic status areas with infrastructure challenges that could increase the chance of dogs being exposed to human feces. Therefore, it may be that in areas where there is good sanitation, dogs are most likely to get Giardia from other dogs. When there are sanitation challenges, dogs may be more likely to be exposed to human types. So, it’s important to know trends in different geographic regions to understand the risk of transmission from pets to humans.