Honglei Sun et al. / Proceedings of the National Academy of Sciences, 2020
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Since 2016, domestic pigs in China have been dominated by the influenza virus, the genome of which combines the characteristics of the strains of the H1N1 swine flu virus that caused the 2009 pandemic and the North American reassortant (combining the genes of several virus species at once) strain, according to Proceedings of the National Academy of Sciences. Laboratory studies have shown that it very easily populates human respiratory tract epithelial cells, and more than 10 percent of pig farm workers have antibodies to it. All this indicates that the new swine flu virus (its strain was called G4 EA H1N1) could cause a new pandemic.
2009–2010 influenza pandemic caused by virus A / H1N1, strain H1N1pdm2009. The first cases of the disease were recorded in the United States and Mexico in April 2009, and then within a few months the infection spread throughout the world. According to the United States Centers for Disease Control and Prevention, 151,700–575,400 people died in the first year of the virus circulation.
A / H1N1 turned out to be especially contagious and dangerous, as it appeared as a result of reassortment – mixing of the genetic material of several viruses. A / H1N1 – a “cross-section” of influenza viruses that infect pigs (so the flu was called swine), birds and humans. When this happens, a new virus often gains the ability to infect species that were previously immune to it. Therefore, it is worthwhile to study which viruses infect animals with which a person often contacts – agricultural, pet, those who often become prey of hunters, and so on. It is their pathogens that are most likely to become human as well due to reassortment.
Therefore, researchers from several scientific institutions in China, led by Jinhua Liu from China Agricultural University, checked which flu viruses circulated among pigs on Chinese farms in the 10 most “pig” provinces in 2011–2018, and determined how they changed over the years. their occurrence. To do this, scientists took nasal swabs from animals killed for meat (29918 samples), and also made homogenate from lung pigs with pronounced signs of respiratory infection (1016 samples). Viruses were detected by polymerase chain reaction: they looked primarily at the genes for hemagglutinins (H in the name of the influenza virus) and neuraminidases (N in the name of the influenza virus). Their sequences were compared with those already known for other strains.
The genome of one of the 179 virus species found, which is closest in structure to the H and N genes to the H1N1pdm2009 strain, was completely sequenced. On tracheal epithelial cell cultures, a person was tested how easily he binds to different versions of the sialoglycoprotein SAα2,6Gal – one of the key molecules for infection with influenza viruses. In addition, the authors analyzed the data of immunological tests of 338 workers of 15 pig farms, during which in 2016–2018 the presence of antibodies to certain strains of influenza viruses was detected. They were compared with the results of similar tests of 230 people not involved in animal husbandry.
It turned out that in 2016, a new strain of the H1N1 influenza virus, which the authors named G4 EA H1N1, began to spread rapidly among Chinese pigs, and since then it has been found more often than others. Apparently, G4 EA H1N1 appeared as a result of reassortment of Eurasian and American A / H1N1 strains. In experiments with cell cultures, he preferably bound to the “human” version of the sialoglycoprotein SAα2.6Gal. An additional series of experiments on ferrets (these animals are often used to evaluate vaccines and drugs against influenza) showed that G4 EA H1N1 is easily transmitted from one animal to another.
In pig farmers, antibodies to the virus were detected in 10.4 percent of cases, in people not related to agriculture, in 4.4 percent of cases. The effect remained after taking into account possible cross-reactivity with H1N1pdm2009 (that is, the variant when the antibodies were to the strain that caused the pandemic in 2009, and not to a new virus). All this (proximity to humans, a large proportion of people with antibodies to the strain, the ease of its binding to the desired glycoprotein and transmission from one individual to another) indicates that G4 EA H1N1 may cause a new pandemic in the coming years. Therefore, the authors point to the need to start periodic inspections of pig farm workers, as well as pigs themselves, for infections associated with influenza viruses as soon as possible.
In 2016, American scientists found that the severity of the flu caused by a specific strain of the virus can be estimated by the year of birth of the patient. It depends on what types of virus a person encountered in childhood, and such information can be obtained by knowing their prevalence in a particular season. Influenza viruses within one group have similar neuraminidase glycoproteins, and if the immune system has already encountered neuraminidases of a specific group, it will most likely be easier to repulse viruses with glycoproteins from the same group.
Svetlana Yastrebova
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