June 30 (UPI) -- A new type of influenza that's becoming more common in pigs is showing a greater ability to spread to humans and could become a human pandemic, Chinese researchers say.
In a study published Monday in the Proceedings of the National Academy of Sciences of the United States of America, researchers said the virus -- which has spread rapidly in pigs over the last six years -- bears similarities to the swine flu that caused a pandemic in 2009 and has "acquired increased human infectivity" among Chinese swine workers who were exposed to infected animals.
The G4 EA H1N1 strain has "all the essential hallmarks of a candidate pandemic virus," they wrote.
The authors, from Shandong Agricultural University and the Chinese National Influenza Center, found that more than 10 percent of workers across 10 provinces tested positive. More than 20 percent of workers between the ages of 18 and 35 were infected.
There is no evidence so far that the virus can spread from human to human, the study said. But the Chinese researchers said they are concerned the virus could mutate and become transmissible. They urged close monitoring of swine populations and agricultural workers.
U.S.-based experts said there is no reason for alarm.
"There's no evidence that G4 is circulating in humans, despite five years of extensive exposure," University of Washington biologist Carl Bergstrom tweeted. "That's the key context to keep in mind."
Columbia University virologist Angela Rasmussen said the G4 virus may have pandemic "potential," but so far it doesn't appear to be any more severe than other types of influenza.
"Sure, this virus meets a lot of the basic criteria but it's not for sure going to cause a hypothetical 2020 flu pandemic, or even be a dominant strain in humans," she tweeted.