The group has published its findings in the latest online issue of the Journal of Virology, according to CIDRAP.

Many human cases had involved live poultry or their environments, and health officials have suspected that poultry infected with low-pathogenic viruses, which typically infect birds without causing symptoms, are the main drivers of the outbreak.

Agriculture officials in China have tested thousands of birds, and have found H7N9 in only a small number of them. These have included chickens, plus a small number of pigeons and ducks. Also, a recent report from Chinese researchers described the isolation of H7N9 from an apparently health tree sparrow collected last spring in Shanghai.

To get a better handle on which species are most likely to be infected and shed enough virus to infect humans, the SEPRL intranasally inoculated chickens, Japanese quail, pigeons, Pekin ducks, mallard ducks, Muscovy ducks, and Emden geese with H7N9 virus. The birds became infected but showed no clinical signs.

Quail and chickens shed the virus at much higher levels and for longer times than other birds. The team found that quail transmitted the virus to their direct contacts but pigeons and Pekin ducks did not.

For all of the species, researchers recovered the virus at much higher levels from oropharyngeal swabs than from cloacal swabs.

Researchers said that the findings show that quail and chickens probably play an important role in spreading the virus to humans.