A new flu virus found in Chinese pigs has become more infectious to humans and needs to be watched closely in case it becomes a potential "pandemic virus," a study said, although experts said there is no imminent threat.
A team of Chinese researchers looked at influenza viruses found in pigs from 2011 to 2018 and found a "G4" strain of H1N1 that has "all the essential hallmarks of a candidate pandemic virus," according to the paper, published by the U.S. journal, Proceedings of the National Academy of Sciences (PNAS).
Pig farm workers also showed elevated levels of the virus in their blood, the authors said, adding that "close monitoring in human populations, especially the workers in the swine industry, should be urgently implemented."
The study highlights the risks of viruses crossing the species barrier into humans, especially in densely populated regions in China, where millions live close to farms, breeding facilities, slaughterhouses and wet markets.
The current coronavirus sweeping the world is believed to have originated in horseshoe bats in southwest China and could have spread to humans via a seafood market in the central city of Wuhan, where the virus was first identified.
'Cannot let our guard down'
The World Health Organization (WHO) will read the Chinese study carefully, spokesperson Christian Lindmeier told a Geneva briefing on Tuesday, saying it was important to collaborate on findings and keep tabs on animal populations.
"It also highlights we cannot let our guard down on influenza and need to be vigilant and continue surveillance even in the coronavirus pandemic," he said.
Chinese Foreign Ministry spokesperson Zhao Lijian told a daily news conference on Tuesday that China was closely following developments. "We will take all necessary measures to prevent the spread and outbreak of any virus," he said.
The study said pigs were considered important "mixing vessels" for the generation of pandemic influenza viruses and called for "systematic surveillance" of the problem.
China took action against an outbreak of avian H1N1 in 2009, restricting incoming flights from affected countries and putting tens of thousands of people into quarantine.
The new virus identified in the study is a recombination of the 2009 H1N1 variant and a once-prevalent strain found in pigs.
But while it is capable of infecting humans, there is no imminent risk of a new pandemic, said Carl Bergstrom, a biologist at the University of Washington.
"There's no evidence that G4 is circulating in humans, despite five years of extensive exposure," he said on Twitter. "That's the key context to keep in mind."
Dr. Andrew Simor, an infectious disease consultant at Sunnybrook Health Sciences Centre in Toronto, said nothing more may happen with G4, but it's important for researchers to keep watching.
"It's early days yet, and clearly it has not demonstrated the ability to spread from person to person," Simor said. "It has not yet been known to cause serious disease in humans."
But people aren't very good at predicting pandemics, he said.
Martha Nelson, an evolutionary biologist at the U.S. National Institutes of Health, said there's a great need to study how viruses in general are able to jump from animals to humans, to improve tracking and surveillance worldwide.