Will a novel swine flu strain cause the next pandemic? – Some critical thoughts on research findings from China
Pig 333 has interviewed Kristien Van Reeth, professor of virology and swine influenza virus expert. She believes these interesting research findings need much more nuance, and tries to put things in perspective.
A novel swine influenza virus variant has become widespread in swine populations in China since 2016 and has “all the essential hallmarks of a candidate pandemic virus”, according to a recent publication in the journal “Proceedings of the National Academy of Sciences of the US” (PNAS). This swine flu strain has been identified and studied by a team of researchers from the Harbin Veterinary Research Institute, China. They claim that “immediate action is needed to prevent the efficient transmission of this H1N1 swine flu variant to humans”. The PNAS article has received abundant media attention.
Will this virus cause the next pandemic? How worried should we be?
Pig 333 has interviewed Kristien Van Reeth, professor of virology at Ghent University, Belgium, and swine influenza virus expert. She believes these interesting research findings need much more nuance, and tries to put things in perspective.
“What makes the virus remarkable and is it really unique?”
The novel virus belongs to the H1N1 subtype. Like many swine influenza viruses, it is a “reassortant”, a hybrid virus with genetic material from two or more existing viruses. In this case, the surface proteins H1 and N1 come from the “Eurasian avian” H1N1 swine influenza virus. The latter virus has been circulating widely in Europe since 1979 and has later spread to Asian countries. The internal genes and proteins are mainly from the 2009 pandemic H1N1 or “Mexican flu” strain, which was also of swine origin. Only one of these proteins has been derived from a North American swine virus. Similar reassortant viruses were previously found in other places in China, as well as in Europe. Thus, this particular reassortant, which is dubbed G4, is not entirely novel. It is remarkable, though, that reassortants with internal genes from the 2009 pandemic H1N1 virus seem to be on the increase.
“Why does the study conclude that the G4 virus has pandemic potential?”
This conclusion is largely based on experiments in ferrets, a common animal model for humans. G4 viruses readily infected and transmitted between ferrets. But ferrets are not humans, and this does not mean that G4 has the capacity for human to human transmission, which is required to start a pandemic. More important, there are dozens of other swine influenza virus variants that have been shown to transmit between ferrets under experimental conditions. Yet, with the exception of the 2009 pandemic H1N1 virus, none of these has turned into a pandemic strain.
The researchers could not detect any antibodies to the G4 strain in more than 90% of the people studied. G4 thus belongs to the category of swine flu strains for which the human population is largely immunologically naïve. This is another requirement for a pandemic influenza virus. But there are several other swine flu strains for which human population immunity is lacking or very low. In other words, there are insufficient arguments that G4 poses unique public health risks in comparison with other swine flu strains.
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