A paper published in the scientific journal PNAS on June 29, 2020 reported that Chinese researchers have identified a new swine influenza virus with pandemic potential . As soon as the news burst out, there was an immediate panic among the crowd.
In the article, we will depict the novel swine flu virus from following aspects:
1. The Discovery of the New Swine Influenza Virus
From 2011 to 2018, researchers from the Shandong Agricultural University, Chinese National Influenza Center, and other scientific research institutions, collected more than 30,000 nose swabs from slaughtered pigs and more than 1,000 types of swabs or lung tissue from bred pigs with respiratory diseases . Among these samples, researchers isolated 179 swine flu viruses, most of which belonged to a strain similar to the H1N1 viruses that caused the 2009 swine flu pandemic  . The new swine influenza virus is a variant genotype 4 (G4) Eurasian avian-like (EA) H1N1 virus, simply termed as G4 EA-H1N1 or G4 virus.
2. What is the New Swine Influenza Virus ?
When multiple influenza viruses infect a single pig, these viruses easily swap genes, a process known as "reassortment," thus generating a new virus strain . The G4 is virtually reassorted by EA-H1N1, pdm/09 H1N1, and triple reassortment H1N1 containing internal elements from avian, human, and swine-origin influenza viruses  . This means the G4 virus contains genes from avian, human, and swine influenza viruses.
Figure：The schematic of G4 structure
The EA-H1N1 viruses have prevalent in Europe and Asia for decades, and they mainly contain 6 genotypes. 2011-2018 data showed that the EA-H1N1 swine influenza virus continuously appeared in the pig population and that the G1 was initially predominant in the pig population from 2011 to 2013. The G4 virus kept showing up since 2013 and become the dominant virus in the Chinese pig population since 2016. At present, the G4 is the single major genotype circulating in China.
3. The Transmissibility of the New Swine Flu Virus
Laboratory experiments showed that the G4 virus could replicate in the upper respiratory tract of humans through the preferential binding to human SAα2, 6Gal receptors. This is a key prerequisite for infecting human cells. And studies found that the G4 virus is effectively contagious and transmissible in ferrets.
Besides, a total of 13 cases of human infection caused by the EA-H1N1 swine influenza virus have been found in the influenza surveillance network in China Since 2010, including 3 cases of G4 genotype virus infection. It is suggested that EA-H1N1 swine influenza viruses, including G4 genotype viruses, can occasionally infect humans, but they can not effectively propagate between humans.
Furthermore, low antigenic cross-reactivity of human influenza vaccine strains with G4 virus indicate that preexisting population immunity does not defense against G4 viruses. Serological surveillance showed that 35 out of the 338 swine farmers were positive for the G4 virus, accounting for 10.4%. The seropositive rate even reached 20.5% among the 18 to 35-year old participants, indicating that the predominant G4 virus has got increased human infectivity that enhances the opportunity.
4. Why Do Experts Predict the New Swine Influenza Virus A Possible Pandemic?
Results on ferrets uncovered that the G4 virus is highly transmissible between ferrets through direct contact and respiratory droplets, as opposed to the G1 EA HIN1 virus. Ferrets were chosen as experimental animal models because their symptoms were similar to those of humans. And the G4 virus led to more serious clinical symptoms on ferrets, including more serious pathological changes in the lung with obvious multifocal consolidation, hemorrhage ＆ edema, and more severe bronchiolitis & bronchial pneumonia. This suggests that G4 viruses may cause more severe infections in humans. No effective vaccines may also note that the G4 virus is susceptible to human infection.
In addition, the G4 virus has currently confirmed to be widely transmitted in the pig population and bears the possibility of jumping from pigs to humans. Therefore, once the G4 virus can spread from person to person, it could cause a pandemic.
5. Be Alert but Do Not Panic
Related experts agreed that the newly reported G4 swine influenza virus is an H1N1 subtype influenza virus evolved from the 2009 H1N1 swine flu virus and is more common in human seasonal influenza and swine influenza. Influenza viruses are ready to mutate, but most of them are not infectious and virulent to humans and animals. The World Health Organization (WHO) emergency project director Ryan also stressed on July 1 that the G4 virus is not new, and has been continuously monitored by the global influenza monitoring network, WHO cooperation center, and Chinese relevant departments since 2011. The information released recently is only the monitoring results at this stage.
Although the probability of infection among the general public is extremely low, it does not mean there is no possibility of infection. Furthermore, no one is immune to this virus. So we should always be alert but not panic.
In daily life, we should pay attention to maintain good personal and environmental hygiene and minimize contact with livestock, poultry, and wild animals. At the same time, we should actively understand the knowledge of influenza prevention and insist on the annual influenza vaccination. The public should consciously abide by the relevant provisions and not buy or carry pork and its products that have not passed the quarantine inspection. In addition, in the process of raw meat processing and cooking, the basic health habits such as separation of raw meat and cooked meat, thorough cooking, keeping the hand clean and so on, are recommended.
In the next step, the experts will continue to strengthen the monitoring and analysis of the pig population, promptly warning and disposing of situations that may cause major outbreaks in humans and animals. China CDC and WHO have developed a variety of candidate vaccines against closely related strains of various types. If any strain with the possibility of effective transmission appears in the population, relevant vaccines can be rapidly developed.
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