New research in microbiology has found that a bug that causes vomiting and diarrhea could possibly be transmitted from humans to dogs — which raises the question of whether dogs can pass it to humans.

Norovirus is the leading cause of gastroenteritis, or "stomach flu," in both children and adults in the United States. A person can be infected by another individual, spoiled food or contaminated surfaces.

Veterinarian Sarah Caddy, a PhD student at the University of Cambridge and head author of the study, explained that her research team found evidence strongly suggesting that dogs have been infected with human norovirus as well.

The virus was discovered to bind to the cells of the canine gut, "the first step required for infection of cells." Caddy believes this occurrence allows dogs to develop immunity to the virus.

Caddy and her team used the outer protein coat, or capsid, of noninfectious human norovirus particles in the study. This is the part of the virus that allows it to bind to a host's cells. The capsids alone cannot facilitate infection because they lack the internal mechanism.

The researchers observed the ability of capsids to attach to tissue samples taken from canine intestines. There were seven unique strains of human norovirus discovered to pose a threat to the gastrointestinal tissue of dogs. The results reveal that an infection is "theoretically achievable," according to Caddy and her colleagues.

The team also checked the theory of whether dogs could be carriers for human norovirus. In their tests of stool samples from 248 dogs, including some taken from dogs with diarrhea, the researchers found no evidence of virus infection. They did, however, find traces of antibodies developed against human norovirus in the blood samples from 43 out of 325 dogs.

The study was unable to identify whether human norovirus can cause clinical sickness in dogs. If it is possible, the researchers found no proof that dogs can transfer the virus to infect humans. Caddy's team notes that other related studies have isolated around 18 virus particles that can cause infection in humans.

"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," Caddy said.

"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."

This study was published in the Journal of Clinical Microbiology. 

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