Anyone who’s had norovirus gastroenteritis knows that it’s pretty nasty. It spreads easily from person-to-person, and from (gross, yes, but true) vomit- and diarrhea-contaminated surfaces. The last thing we need is another source of infection to worry about. The potential for dogs to be sources of norovirus has gotten a lot of attention (often misguided) over the past few days, because of a recent research paper from the UK (Caddy et al, Journal of Clinical Microbiology 2015). The key components of the study and its results were:

• Stool samples were collected from dogs with and without diarrhea. The virus wasn’t found in any of 248 samples
• Blood samples were collected and tested for antibodies against norovirus: 33% were positive, suggesting the dogs had been exposed to norovirus in the past and mounted an immune response. That doesn’t mean they were sick or able to infect others, just that they were exposed and their bodies reacted to the virus, as they should. This has been reported before.
• Saliva samples were collected from a small group of dogs to test the virus’s ability to attach to canine saliva.  Norovirus was able to attach to saliva from all dogs.
• Intestinal tissues from some research dogs were collected and tested for the ability of norovirus to attach. The virus could attach to all the intestinal samples.

Surprisingly, they didn’t test dogs owned by people with norovirus infection. I would have thought that would be the highest yield way to determine if dogs can be infected and shed the virus. It’s harder to do a study like that, since you have to have a way to identify infected households and get samples quickly, but it would be the most informative approach. You could test 248 people in the general population and not find norovirus, but that doesn’t mean people aren’t susceptible or able to shed the virus. Testing dogs that have been exposed to people with norovirus to see if they are able to shed the virus, and therefore be a potential source of infection, is an important next step to determine whether there is any potential issue here. So, should we be concerned?

Probably not. This study showed that dogs can be exposed (no surprise there) and that their bodies can respond to the virus. Mounting an immune response doesn’t mean that the virus was able to grow in the body and be shed. It’s interesting information but far from evidence that dogs are a concern. The authors rightly conclude “In summary, whereas HuNoV infection of dogs has been shown to be theoretically 
possible, the risk of this causing significant clinical disease in dogs is believed to be 
very low. 
” There are a lot of things that dogs get exposed to that they can’t then pass on. If dogs could infect us with everything to which they could produce and antibody response, we’d be in trouble. So, it’s an interesting piece of research that gives more support to the notion that we share a lot with our animals. However, I don’t think it indicates much to be worried about at this point.