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Even though China's avian flu, H7N9 has calmed down significantly, researchers have continued to study the strain to prepare for the possibility of a pandemic. H7N9, identified in February, has already infected 133 people with 43 fatalities. Health officials have stated that the majority of these cases involved direct contact with poultry. Human to human transmission of this flu appears to be very limited with only one case between a father and daughter. In order to understand the strain, researchers decided to trace the root of the outbreak.

For this study, researchers from the Shantou University Medical College and the University of Hong Kong collected samples from 1,341 sources, which included chickens, ducks, geese, pigeons, partridges, quail, fecal matter and water from live poultry markets. The researchers looked at the genetic makeup of the viruses from each animal and compared them. The researchers concluded that, "domestic ducks seem to act as key intermediate hosts by acquiring and maintaining diverse influenza viruses from migratory birds."

"This probably led to outbreaks in chickens resulting in the rapid spread of the [virus] through live poultry markets which became the source of human infections," the researchers continued according to BBC News.

The researchers also discovered that there are other versions of H7 flu viruses that are circulating in the birds but have not infected humans. These flu viruses "may [potentially] pose threats beyond the current outbreak." Although these strains have only circulated amongst the animals, the researchers noted that one particular strain, H7N7, has the ability to infect ferrets. Ferrets are often used to test a virus's ability to reach humans.

"The discovery ... reminds us that even if H7N9 does not return, there are risks lurking amongst the great diversity of avian influenza viruses," said Peter Horby, a bird flu expert at the Oxford University Clinical Research Unit in Hanoi, Vietnam according to Reuters. Horby was not involved in the research.

The findings of this study could hopefully prepare health officials and governments for any potential threats lurking in these animals. The study was published in Nature.