◎ Science and Technology Daily reporter Zhang Jiaxing
On April 26, the National Health Commission informed that a 4-year-old boy in Henan was infected with the H3N8 avian influenza virus. The subsequent medical observation and sampling test results of close contacts of infected people showed no abnormalities.
National Health Commission pointed out in the notice that H3N8 virus has been detected on horses, dogs, birds and seals worldwide, but no human cases of H3N8 have been reported.
Why can the H3N8 avian influenza virus that should have been transmitted in avians cause disease in humans? How does this virus spread across species? Will human-to-human transmission occur in the future? Why can
H3N8 cause illness?
The COVID-19 pandemic has made many people understand that if the protein "key" on the surface of the virus can open the protein "lock" on the surface of human cells, it can invade cells and cause infection.
The "key" of the new coronavirus is the S protein, and one of the "keys" of the influenza virus is the HA protein. These proteins are like barbs on "Tribula" that can hook cells and fuse themselves into it. However, the receptors that human influenza virus and avian influenza virus can "hook" are different.
Academician of Chinese Academy of Sciences Academician Gaofu makes a detailed explanation in his popular science book specifically interpreting influenza viruses: the main cellular receptor of the HA protein of avian influenza virus is the α-2,3-galactosinosialic receptor, while the main cellular receptor of the human influenza HA protein is the α-2,6-galactosinosialic receptor. The human upper respiratory tract cells contain the receptor , and the lower respiratory tract has the receptor in the front. Usually, avian influenza viruses are not easy to penetrate deep into the human lower respiratory tract. Even if they arrive, they will be bound by tissue mucus and are difficult to spread.
But it is not ruled out that some avian influenza viruses have the ability to bind α-2,6-galactosine sialic acid receptors, and H3N8 is one of them.
In the academic paper "Research on the Biological Characteristics of H3N8 Avian Influenza Viruses in China from 2009 to 2013", it conducted receptor-binding specific analysis on 29 H3N8 avian influenza viruses that appeared in my country, and found that they have the ability to bind to both receptors. Researchers believe that the current prevalence of H3N8 avian influenza virus in my country has the potential risk of infecting humans and spreading between people.
shows that some H3N8 avian influenza viruses themselves have the ability to infect people, and the real infection and cause the disease is also related to the size of the viral load in the infected person, the physical conditions of the infected person themselves, etc.
How does influenza virus spread across species?
"Influenza viruses achieve cross-species transmission generally require the accumulation of core mutations." A researcher who continues to track the evolution of avian influenza viruses told Science and Technology Daily that the virus accumulates mutations in the process of transmission and evolution, which may lead to cross-species transmission.
Take H7N9, which was transmitted in my country in 2013 as an example. Relevant units have found that it is made of avian influenza viruses in chickens and ducks. Gao Fu explained in detail in the book: The tracing of the H7N9 virus found that the virus may be reassorted directly from the chicken body, and the ability to infect humans directly evolved into a new type of influenza virus.
In addition, due to the diverse types of influenza virus hosts, pigs, dogs, etc. are considered as "mixers" for their redistribution. A report on "Research Progress in the Research of H3N2 and H3N8 Subtypes of Canine Influenza Virus" shows that most histiocytes in dogs have sialic acid receptors for human and avian influenza viruses. Influenza viruses infected with dogs have undergone multiple amino acid-specific mutations in the HA site, which is speculated that they are the cause of cross-species transmission. Will
be spread among the crowd in the future?
The notice from the National Health Commission shows that experts have been organized to conduct risk assessments, believing that the epidemic is an occasional cross-species transmission from poultry to humans, and the risk of large-scale transmission and epidemics is low.
Will it cause human transmission after cross-species transmission? The aforementioned researchers said that the former is a necessary condition for the latter, but not a sufficient condition. In other words, interpersonal transmission is only possible after cross-species transmission occurs, but it does not necessarily lead to human transmission. According to literature reports, only a few avian influenza viruses spread across species to humans and have caused very limited individual family clustering cases.In terms of comprehensive judgment, the possibility and probability of H3N8 transmission of humans and humans is unknown, so we should be vigilant. The public should still try to avoid direct contact with live poultry products in daily life, let alone contact with sick and dead poultry.
At the same time, high-tech means such as big data and model analysis have been used to track and alert the avian influenza virus. Research by Chinese scholars previously published in " Proceedings of the National Academy of Sciences " shows that by analyzing the variation of avian influenza , the transmission and evolutionary history of the virus in various provinces can be calculated, and the transmission laws of the virus across the country can be summarized, and the relationship with live poultry trade and wild bird migration may be effectively predicted.
Source: Science and Technology Daily
