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.
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 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.
“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.
James Wood, head of the department of veterinary medicine at Cambridge University, said: “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.”
A zoonotic infection is caused by a pathogen that has jumped from a non-human animal into a human.