Researchers are plotting the evolution of a strain of avian flu currently spreading in China, finding that it emerged in tandem with a similar flu that can infect mammals.

A report has been published revealing that H7N9 grew up in tandem with H7N7, authors of the study published in Nature say that their finding reinforces the notion that avian viruses are constantly mixing and exchanging genetic material — a process known as reassortment — in Asian poultry markets.

Experts have raised concerns that such virulent melting pots might spawn a reassortment of H7N7 that could spread to humans.

Professor Yi Guan is an influenza specialist at the University of Hong Kong and lead author of the study. Guan says better surveillance of Chinese bird populations is needed to monitor the emergence of dangerous viruses. He says China has a “very different influenza ecosystem from other countries,” where the virus has infected 135 people and resulted in 44 deaths since February.

To complete the recently-published study, a team of researchers collected swab samples from over a thousand birds, including chickens, ducks, geese, pigeons, partridges and quails, plus water and faecal samples from bird markets. Reportedly some 10% of samples tested positive for an influenza virus; of those, 15% were an H7 virus.

When the team sequenced and compared the two viruses’ genomes they found H7N9 and H7N7 to be hybrids of previously identified wild Eurasian waterfowl strains. The scientists believe those viruses swapped genes in domestic ducks before jumping to chickens, where they traded genes with a common virus, H9N2.

Further details from the report are accessible via the journal Nature.