Researchers have discovered a strain of swine flu virus in China with all the characteristics capable of causing a future pandemic, according to a study published Monday in the American scientific journal PNAS . A disturbing announcement, in the midst of a coronavirus epidemic.
The viruses are called G4 and are genetically descended from the H1N1 strain, which caused a pandemic in 2009: they "have all the essential traits showing high adaptability to infect humans", write the authors, scientists from Chinese universities and the Chinese Center for Disease Prevention and Control.
The work presented is bulky: from 2011 to 2018, 30,000 nasal swabs were taken from pigs in slaughterhouses in 10 Chinese provinces and in a veterinary hospital, making it possible to isolate 179 swine flu viruses. The majority were of the new variety, which has become dominant in pigs since 2016.
The researchers then carried out various experiments in the laboratory and on ferrets, animals widely used in influenza research because their symptoms are comparable to those of humans: they have a fever, cough and sneeze. They observed that G4 viruses were more infectious, replicated in human cells and caused more severe symptoms in ferrets than other strains. Furthermore, according to in vitro tests, the immunity obtained after contact with human seasonal influenza viruses does not protect against G4.
Infected workers
The other bad news is that workers and people working with pigs were relatively numerous to have been infected, 10.4%, according to blood tests which looked for the presence of antibodies to the virus. 4.4% of the general population also appeared to be infected. The virus is therefore already believed to have passed to humans, scientists say, but there is no evidence that it can be transmitted from human to human. Today is their fear.
"Pandemics occur when influenza A viruses with a new HA surface antigen become capable of being transmitted from human to human," the researchers conclude. "The concern is that infections of humans with the G4 viruses do not lead to human adaptation and do not increase the risk of a human pandemic."
There is an urgent need, they say, to put in place surveillance of populations working in contact with pigs. "The work is a salutary reminder that we are constantly running the risk of the emergence of zoonotic pathogens, and that farm animals, with which humans are more in contact than with wild animals, are the source of pandemic viruses important, "said James Wood, head of the department of veterinary medicine at the University of Cambridge.
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