Study indicates that dogs may harbor, transmit human norovirus

NATIONAL REPORT — Recent research has shown that canines can carry norovirus (NoV), which is a primary cause of gastroenteritis in the United States and a major cause of diarrheal disease among people.

According to novel research published online in the Journal of Clinical Virology on Jan. 12, 2012, study findings showed that the canine may transmit human strains of norovirus to people within the pet's home environment. It's a notable finding, considering that virus transmission typically happens through the fecal-oral route from one human to another or via infected food, water or surface areas.

The study, led by Dr. Maija Summa and conducted at Finland's University of Helsinki's Department of Food Hygiene and Environmental Health, reviewed 92 fecal samples from dogs in homes where a dog or other family member was vomiting or had diarrhea (both are frequent symptoms of NoV infection). Human strains of norovirus (HuNoV) were detected in four samples from animals that had direct contact with symptomatic people. All NoV-positive dogs lived in households with small children and two dogs showed mild symptoms.

Carl-Henrik von Bonsdorff, study co-author and a faculty member at the University of Helsinki's Faculty of Veterinary Medicine, noted that researchers originally thought that animals did not transmit human noroviruses because there were powerful obstacles within the species to potentially prevent transmission. But based on the new findings, researchers are re-investigating animal reservoirs.

Study results showed that two dogs whose feces were positive for human norovirus also presented with mild, infection-related symptoms. The results also indicated that HuNoVs can live inside the canine gastrointestinal tract.

Researchers believe dogs most likely contract the virus throught contact with younger children. The virus is found in the greatest concentrations in feces but also can be spread via vomit and saliva. But dogs could also pick up the virus by sniffing, eating or licking affected materials outside the home, too.

Nevertheless, the most common way to transmit the virus is still human to human, according to von Bonsdorff.

"Our results suggest that HuNoVs can survive in the canine gastrointestinal tract. Whether these viruses can replicate in dogs remains unresolved, but an association of pet dogs playing a role in transmission of NoVs that infect humans is obvious," the study concludes.

Future research may examine transmission routes of the virus.