Researchers in China have discovered a new type of swine flu that is capable of triggering a pandemic, according to a study in the US science journal PNAS, although experts said there is no imminent threat.
Named G4, it is genetically descended from the H1N1 strain that caused a pandemic in 2009.
It possesses “all the essential hallmarks of being highly adapted to infect humans”, said the authors, scientists at Chinese universities and China’s Center for Disease Control and Prevention, in the study published on Monday.
Between 2011 and 2018, researchers took 30,000 nasal swabs from pigs in slaughterhouses in 10 Chinese provinces and in a veterinary hospital, allowing them to isolate 179 swine flu viruses.
The majority were of a new kind that has been dominant among pigs since 2016.
The researchers then carried out various experiments – including on ferrets, which are widely used in flu studies because they experience similar symptoms to humans.
G4 was observed to be highly infectious, replicating in human cells and causing more serious symptoms in ferrets than other viruses do.
Tests also showed that any immunity humans gain from exposure to seasonal flu does not provide protection from G4.
More than one in 10 swine workers in the new study had already been infected, according to antibody blood tests which showed exposure to the virus.
The tests also showed that as many as 4.4% of the general population also appeared to have been exposed.
The virus has therefore already passed from animals to humans but there is no evidence yet that it can be passed from human to human – the scientists’ main worry.
The World Health Organization (WHO) will read the Chinese study carefully, spokesman Christian Lindmeier told a Geneva briefing on Tuesday, saying it was important to collaborate on findings and keep tabs on animal populations.
Chinese Foreign Ministry spokesman 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 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.
“It is of concern that human infection of G4 virus will further human adaptation and increase the risk of a human pandemic,” the researchers wrote.
The authors called for urgent measures to monitor people working with pigs.