Human norovirus can cause an immune response in dogs so it leads to obvious concern over whether or not dogs can transmit it to other people.

Norovirus, which causes vomiting and diarrhea, is extremely contagious among humans. It infects 19-21 million Americans annually - more than six percent of the US population - according to the CDC. Those infections may result in as many as 71,000 hospitalizations, and 800 deaths.

Since dogs can mount an immune response to human norovirus, that strongly suggests that those dogs have been infected with the virus, and the human norovirus can bind to the cells of the canine gut, which is the first step required for infection of cells, acccording to a new paper which used non-infectious human norovirus particles, consisting solely of the virus' outer protein, called the capsid.

The capsid is the part of the virus that binds to host cells. By itself, it is non-infectious because it lacks genetic material and the non-infectious capsid is the basis for a new norovirus vaccine which is being tested in clinical trials, said Sarah Caddy, VetMB, PhD, MRCVS, a research fellow at the University of Cambridge and first author of the new paper, but it is not known just how much of a problem canine infection and transmission may represent for humans. Despite dogs' apparent susceptibility, the investigators failed to find norovirus in canine stool samples, including those from dogs with diarrhea. They found it in serum samples of under 15 percent of 325 dogs tested.

It is a concern if dogs can transmit it to humans - it only takes 18 virus particles to cause human infection - but first it must be determined if the norovirus can cause clinical disease in dogs. 

"There are plenty of anecdotal cases of dogs and humans in the same household, having simultaneous gastroenteritis, but very little rigorous scientific research is conducted in this area," said Caddy.

We know that all those cruise ships where people got sick can't blame their pets.

Citation: Caddy SL, de Rougemont A, Emmott E, El-Attar L, Mitchell JA, Hollinshead M, Belliot G, Brownlie J, Le Pendu J, Goodfellow I, 'Evidence for human norovirus infection of dogs in the UK', J Clin Microbiol. 2015 Apr 1 2015 doi: 10.1128/JCM.02778-14