This is the result of a study from a team of researchers led by Tommy Tsan-Yuk Lam, Jia Wang and Yongyi Shen at Shantou University Medical College in China.

According to their research, backed by a large team from the medical college and other institutions, they found that neither the source populations of the H7N9 outbreak lineage nor the conditions for its genesis were fully known.

Preliminary analyses suggested that the virus was a merging and mutating of H7, N9 and H9N2 avian influenza viruses, and carried some amino acids associated with mammalian receptor binding, raising concerns of a new pandemic.

By using a combination of active surveillance, screening of virus archives, and evolutionary analyses, the researchers were able to show that H7 viruses probably transferred from domestic duck to chicken populations in China on at least two independent occasions.

The researchers were then able to show that the H7 viruses merged with the enzootic H9N2 viruses to generate the H7N9 outbreak lineage.

It then mutated to a related and previously unrecognised H7N7 virus.

The novel H7N9 influenza A virus first detected in March 2013 has since caused more than 130 human infections in China, resulting in 40 deaths.

“We show that the H7 viruses subsequently reassorted with enzootic H9N2 viruses to generate the H7N9 outbreak lineage, and a related previously unrecognized H7N7 lineage,” the research team say in their paper published in the journal Nature.

“The H7N9 outbreak lineage has spread over a large geographic region and is prevalent in chickens at live poultry markets, which are thought to be the immediate source of human infections.

“Whether the H7N9 outbreak lineage has, or will, become enzootic in China and neighbouring regions requires further investigation.”

The discovery of a related H7N7 influenza virus in chickens that has the ability to infect mammals experimentally, suggests that H7 viruses may pose threats beyond the current outbreak, the research team concludes.

“The continuing prevalence of H7 viruses in poultry could lead to the generation of highly pathogenic variants and further sporadic human infections, with a continued risk of the virus acquiring human-to-human transmissibility,” they say.