Chinese scientists report a new influenza virus that has spread to swine populations and has already infected humans. This increases the risk of a new pandemic virus, said Honglei Sun from the China Agricultural University in Beijing and colleagues in the online edition of PNAS (Proceedings of the National Academy of Sciences) on June 29.
Because domestic pigs are intermediate hosts for influenza viruses and, due to their contact with humans, birds and other animals, are regarded as “mixing vessels” in which potentially dangerous virus mutations can occur for humans, they are subject to surveillance in China. Sun and co-workers found a genotype that was reassorted from three virus lines. It contains genetic material from the 2009 H1N1 swine flu virus, bird flu viruses and a North American H1N1 strain. The influenza A virus is referred to as “genotype G4 reassortant Eurasian avian-like (EA) H1N1”. This G4 genotype has prevailed in Chinese pig populations since 2016, the veterinarians write. China has the largest domestic pig population in the world. The virus has become dominant in ten Chinese provinces.
Increased G4 seroprevalence among pig factory workers
“It is worrying that pig factory workers have an increased G4 seroprevalence,” the report says. 35 out of 338 tested workers (10.4 percent) were positive for G4 EA H1N1, among young workers (18 to 35 years old) even 20.5 percent. This indicates that people are already more susceptible to infections. And this in turn increases the likelihood that the virus will continue to adapt to humans, so that it can theoretically be transmitted from person to person.
Whether this will actually happen is by no means certain, said virologist and influenza researcher Professor Robert Webster from Memphis, Tennessee, to the science magazine “Science”. “We cannot know whether a pandemic can result from it until it is there.” And the journal quotes the biologist Professor Edward C. Holmes from the University of Sydney, Australia: “This situation must definitely be accurate be monitored.”
Genetic selection advantage in pigs?
EA H1N1 viruses have been circulating in Asian and European pig populations for decades. From 2011 to 2013, a G1 genotype was predominant, Sun and co-workers explain in their publication. Since 2014, G4 and G5 genotypes have been gradually replacing the EA H1N1 genotypes, and the rate of isolated G4 genotypes in pigs with respiratory symptoms increased rapidly year after year. This indicates that these influenza viruses have a genetic selection advantage in pigs. This makes them an increasing problem in fattening farms, which inevitably also confronts people with the virus.
In China, five EA-like swine flu cases have been reported, including three infants and two patients with a G4-like EA H1N1 virus who had close contact with pigs. According to the Chinese scientists, the G4 virus has all the hallmarks of adaptation to humans. This increases the risk of an influenza pandemic.