The researchers discovered G4 during a pig surveillance program that ran between 2011 and 2018, in which they collected more than 30,000 samples of pig nasal swabs from slaughterhouses and veterinary teaching hospitals in 10 Chinese provinces.
From these samples, the researchers identified 179 swine influenza viruses, but not all of them were of concern. Some only appeared one year out of the show's seven, or eventually declined to non-threatening levels.
But the G4 virus continued to appear in pigs, year after year, and even showed a sharp increase in the swine population after 2016.
Other tests showed that G4 can infect humans by binding to our cells and receptors, and can rapidly replicate within our airway cells. And although G4 contains H1N1 genes, people who received seasonal flu vaccines will not have immunity.
G4 already appears to have infected humans in China. In Hebei and Shandong provinces, both places with high numbers of pigs, more than 10% of pig workers on pig farms and 4.4% of the general population tested positive in a 2016-2018 survey.
There is still no evidence that G4 can spread from person to person, but researchers warned that the virus was on the rise among pig populations and could "pose a serious threat to human health." Transmission of the pig virus to human could "lead to serious infection and even death," said the study, which called for stricter surveillance and control of the virus's spread.
Surveillance and discovery
After 2009, the human H1N1 virus spread to pigs around the world, and genes mixed in new combinations, creating new viruses like G4.
"It is worrisome that human G4 virus infection promotes human adaptation and increases the risk of a human pandemic," said the study authors, who are based at several Chinese institutions, including Shandong Agricultural University and the National Center for Influenza in China.
To decrease the risk of this happening, farmers and Chinese authorities should control the spread of the virus among pigs and closely monitor people working with the animals, the team said.
The central Chinese city of Wuhan is ground zero for the new coronavirus, which emerged in December last year and began to spread internationally in January. The outbreak led China to impose strict blockades across the country, close local and provincial borders, and order residents to stay at home.
The country began reopening in March after largely containing the virus, but new outbreaks and local broadcasts in recent weeks have caused some cities to be blocked again.