Another strain of influenza has been detected in China - and researchers say it has the potential to infect humans and cause a fresh global health crisis.
The new flu virus - known only as G4 EA H1N1 - has so far only been found in pigs, but scientists say it has "all the hallmarks" of being highly adapted to humans and capable of triggering a pandemic in a similar fashion to COVID-19.
The research - published on Monday in scientific journal Proceedings of the National Academy of Sciences - suggests Chinese pig farmers already show elevated levels of the virus, which could eventually cause widespread disease.
"Controlling the prevailing G4 EA H1N1 viruses in pigs and close monitoring in human populations, especially the workers in swine industry, should be urgently implemented," a summary of the study reads.
The Chinese researchers say their study shows the G4 EA H1N1 virus has already "acquired increased human infectivity".
"Such infectivity greatly enhances the opportunity for virus adaptation in humans and raises concerns for the possible generation of pandemic viruses," they say.
Professor James Wood, Head of Veterinary Medicine at Cambridge University, says the discovery of the virus is a further warning of the threat pathogens pose to humanity.
"The work comes as a salutary reminder that we are constantly at risk of new emergence of zoonotic pathogens, and that farmed animals - with which humans have greater contact than with wildlife - may act as the source for important pandemic viruses," he said.
Dr Alice Hughes, an Associate Professor at the Chinese Academy of Sciences, says hygiene standards and feeds including hormones and steroids are "likely to be contributory factors to compromised immune systems and the potential of viruses to spread".
China is home to about half the global pig population, according to Statista. It is the largest pork producer in the world, producing about 55 million metric tons of the meat each year.