Norovirus, often called food poisoning by lay people, infects 6% of the U.S. population and results in 800 deaths annually, according to the Centers for Disease Control (CDC). It may also be infecting canine companions according to a recent study.

The study, published April 1 in the Journal of Clinical Microbiology, a publication of the American Society for Microbiology, raises the possibility of dog-to-human transmission of the virus, said first author Sarah Caddy, VetMB, PhD, MRCVS, a veterinarian and PhD student at the University of Cambridge and Imperial College, London, UK. (Caddy will also be a junior research fellow at the University of Cambridge in August.)

Caddy’s research showed that some dogs can mount an immune response to human norovirus. 

"This strongly suggests that these dogs have been infected with the virus," said Caddy. "We also confirmed that that human norovirus can bind to the cells of the canine gut, which is the first step required for infection of cells."

Caddy and collaborators performed the latter research using non-infectious human norovirus particles, which consist solely of the virus' outer protein, or 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.

The non-infectious capsid is the basis for a new norovirus vaccine, which is being tested, in clinical trials, said Caddy.

Caddy is uncertain 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 only about one seventh of 325 dogs tested.

Whether human norovirus can cause clinical disease in dogs is unclear. Assuming that dogs become infected with human norovirus as noted in this study, study, it also remains unknown whether they could shed the virus in quantities sufficient to infect humans—although clinical investigators have estimated that as few as 18 virus particles can cause human infection.

Conversely, whether dogs play a role in the epidemiology of some outbreaks of human norovirus is uncertain. Some of the biggest outbreaks occur in places from which dogs are absent, such as on cruise ships and in hospitals.

"Until more definitive data is available, sensible hygiene precautions should be taken around pets, especially when gastroenteritis in either humans or dogs is present in a household," said Caddy.