Pigs are considered important hosts or “hybrid containers” for the production of pandemic influenza viruses. Systematic monitoring of swine flu viruses is critical to early warning and preparation for the next potential pandemic. The team from China has discovered by monitoring the nose swabs of nearly 30,000 pigs from 2011 to 2018: a recombinant influenza virus, G4 EA H1N1, has dominated the domestic swine flu virus since 2016 and has the potential to become endemic in the population. The research team recommends that the spread of the G4 EA H1N1 virus in pigs be rapidly controlled and that farmers be closely monitored.
The above findings come from the latest paper, Prevalent Eurasian-like H1N1 swine influenza virus with 2009 viral viral genes into the human infection, a paper published june 29 local time in the Proceedings of the National Academy of Sciences (PNAS). The paper’s authors are Professor Liu Jinhua and Gao Fu, Director of the School of Zoology of China Agricultural University, and First Author Sun Honglei, Associate Researcher in the Department of Preventive Veterinary Medicine, School of Animal Medicine, China Agricultural University.
The monitoring took eight years across 10 provinces and cities. Specifically, the researchers collected 29918 pig nose swabs from pig farms in Anhui, Beijing, Hebei, Heilongjiang, Henan, Jiangsu, Jilin, Liaoning, Shandong and Tianjin, as well as 1,016 pig-nose swabs or lungs with respiratory symptoms. The researchers identified a recently occurring genotype 4 (G4) recombinant Eurasian poultry influenza (EA) H1N1 virus (G4 EA H1N1, or G4 virus) that has an internal gene derived from the 2009 H1N1 pandemic and triple recombination (TR), which has dominated the pig population since 2016. Recombination refers to the easy exchange of genes when multiple influenza viruses infect the same pig, a process known as “recombination”.
Similar to the 2009 swine flu virus, the G4 virus binds to human-type receptors, produces more sub-viruses in human airway skin cells, and exhibits efficient infectious and aerosol transmission in ferrets, a popular animal model for the study of human influenza.
In addition, the low antigen cross-reaction of the human influenza vaccine strain with The G4 recombinant EA H1N1 virus indicates that existing population immunity does not provide protection against the G4 virus. Further serological monitoring of occupational contact populations showed that 10.4% (35/338) of pig workers were positive for the G4 EA H1N1 virus, especially for participants between the ages of 18 and 35, with a seropositive rate of 20.5% (9/44), indicating increased human infectiousness, mainly G4 EA H1N1 virus. This infectiousness greatly increases the chances of the virus adapting in humans and raises concerns about the potential for pandemic viruses.
According to Evolutionary Tree Analysis, the EA H1N1 virus has six genotypes of G1-G6. G1 was the original EA H1N1, and other genotypes, including G4, were created by the replacement or mutation of certain genes between 2011 and 2018.
The G4 virus has been around since 2013, becoming mainstream in 2016 and accounting for an absolute majority in 2018, according to the results of the pig-nose swab analysis.
“From the current data, this appears to be a swine flu virus that is about to appear in humans,” said Edward Holmes, an evolutionary biologist at the University of Sydney who studies pathogens, as quoted by the Science website. “But the study has its limitations, which are that the sample is not large enough, with 500 million pigs in China. The study only gives a small insight into the strain of swine flu.
In a household survey, researchers found that 4.4 percent of the 230 respondents had G4 antibodies, more than double the proportion among pig workers, the paper said. In addition to increasing surveillance, Sun honglei said it makes sense to develop a G4 vaccine for pigs and humans.