This rather sensational title is from a Murdoch University (Australia) news article regarding a study of intestinal parasites in Australian dogs. It certainly grabs one’s attention. For me, the article brings to mind two different trains of thought:
1) Far more than 10% of dogs could make their owners sick. Be it dogs, cats, rabbits, iguanas or anything else, every pet is carrying something that could cause an infection in a person in certain situations. If a study says that only X% of dogs/cats carry some sort of zoonotic pathogen (and X isn’t 100), then they didn’t test hard enough or they didn’t test for enough things. Every animal – and every person – is carrying something that can make others sick. However, even though all pets carry zoonotic pathogens, most of these are of minimal concern to most people, and therefore the likelihood of most pets making their owners sick is relatively low. We have to remember, however, that there is no such thing as "no risk" pet contact, just as there’s no such thing as "no risk" contact between people.
2) The 10% figure from this study refers to the percentage of dogs that were shedding the intestinal parasite Giardia. This parasite can cause disease in people and that’s why there is concern. However, the 10% figure isn’t really surprising, as the press release states, because previous studies from different areas in the world have reported Giardia shedding by 7-10% of healthy dogs. The real question is, what is the risk to people from these dogs? The short answer is: we don’t know. Not all types of Giardia found in dogs are able to cause disease in people. Figuring out what type of Giardia a dog is shedding requires fairly specialized testing, and there’s no indication that this was performed for this study. If most dogs carry strains that don’t infect people, then the risk is very different than if most dogs were carrying zoonotic strains. Furthermore, we don’t know how often Giardia is transmitted between people and pets in any situation. At this point, there is actually very little information regarding transmission of Giardia from pets to people. That being said, it’s better to err on the side of caution and assume that Giardia could be transmitted from pets to people, at least until we have good evidence otherwise.
I’m not trying to dismiss the potential concerns about Giardia in dogs, nor do I think the study isn’t useful. It’s an interesting study that has provided new information about intestinal parasite carriage in dogs in Australia. However, it doesn’t really tell us anything new about the risk to humans.
Professor Andrew Thompson, Murdoch’s Head of Parasitology gives some good advice when he states "As a result of these new findings, dog owners should be aware of the signs of Giardia and how to prevent infection in their pets. If you suspect that your dog may be infected with Giardia, it is important you visit your local vet for a full diagnosis.”
More information about Giardia can be found on the Worms&Germs Resources page.
Photo: Giardia trophozoite (CDC Public Health Image Library #8698/Janice Carr)