By Jon CohenJun
What the world doesn’t need now is a pandemic on top of a pandemic. So a new finding that pigs in China are more and more frequently becoming infected with a strain of influenza that has the potential to jump to humans has infectious disease researchers worldwide taking serious notice. Robert Webster, an influenza investigator who recently retired from St. Jude Children’s Research Hospital, says it’s a “guessing game” as to whether this strain will mutate to readily transmit between humans, which it has not done yet. “We just do not know a pandemic is going to occur until the damn thing occurs,” Webster says, noting that China has the largest pig population in the world. “Will this one do it? God knows.”
When multiple strains of influenza viruses infect the same pig, they can easily swap genes, a process known as “reassortment.” The new study, published today in the Proceedings of the National Academy of Sciences, focuses on an influenza virus dubbed G4. The virus is a unique blend of three lineages: one similar to strains found in European and Asian birds, the H1N1 strain that caused the 2009 pandemic, and a North American H1N1 that has genes from avian, human, and pig influenza viruses.
The G4 variant is especially concerning because its core is an avian influenza virus—to which humans have no immunity—with bits of mammalian strains mixed in. “From the data presented, it appears that this is a swine influenza virus that is poised to emerge in humans,” says Edward Holmes, an evolutionary biologist at the University of Sydney who studies pathogens. “Clearly this situation needs to be monitored very closely.”
As part of a project to identify potential pandemic influenza strains, a team led by Liu Jinhua from the China Agricultural University (CAU) analyzed nearly 30,000 nasal swabs taken from pigs at slaughterhouses in 10 Chinese provinces, and another 1000 swabs from pigs with respiratory symptoms seen at their school’s veterinary teaching hospital. The swabs, collected between 2011 and 2018, yielded 179 swine influenza viruses, the vast majority of which were G4 or one of five other G strains from the Eurasian avianlike lineage. “G4 virus has shown a sharp increase since 2016, and is the predominant genotype in circulation in pigs detected across at least 10 provinces,” they write.
Sun Honglei, the paper’s first author, says G4’s inclusion of genes from the 2009 H1N1 pandemic “may promote the virus adaptation” that leads to human-to-human transmission. Therefore, “It’s necessary to strengthen the surveillance” of pigs in China for influenza viruses, says Sun, also at CAU.
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