A new flu virus found in Chinese pigs has become more infectious to humans and needs to be watched 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 US journal, Proceedings of the National Academy of Sciences .

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 populated regions in China, where millions live in close proximity to farms, breeding facilities, slaughterhouses and 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.

“China is closely following the developments in regard to this matter. We will take all necessary measures to prevent the spread and outbreak of any virus,” Chinese foreign ministry spokesman Zhao Lijian said.