According to data from the European Food Safety Authority, the European Centre for Disease Prevention and Control and the EU Avian Influenza Reference Laboratory, large-scale bird flu has occurred in Europe since June in 2022, affecting 37 European countries, from Norway to Sri Lanka. The Valbar Islands to Ukraine, the largest geographic extent ever recorded. Europe has been devastated by what has been described as the “largest ever” bird flu outbreak, with nearly 48 million birds culled. Research on the current situation of the epidemic has found that the avian influenza epidemic in Europe this time is mainly caused by H5N1.
Introduction of Avian influenza
Avian influenza is a disease syndrome caused by the infection of birds by influenza A viruses of the family Orthomyxoviridae. Influenza A virus has a wide host spectrum and can naturally infect mammals such as pigs, horses, minks, seals, whales, and birds, as well as humans. It spreads rapidly and is epidemic or pandemic. At the same time, influenza A virus also has the characteristics of easy recombination and high mutation of genes. According to the different virulence of the virus, avian influenza is usually divided into three categories: highly pathogenic avian influenza (HPAI), low pathogenic avian influenza (LPAI) and non-pathogenic avian influenza. Currently, HPAI is limited to diseases caused by subtypes H5 and H7.
The outer membrane of influenza virus particles is covered by two types of surface glycoproteins, one is phytohemagglutinin (ie H) and the other is neuraminidase (ie N). H is divided into 16 subtypes and N is divided into 9 subtypes. All human influenza viruses can cause avian influenza, but not all avian influenza viruses can cause human influenza. It has been confirmed that a total of 8 avian influenza viruses can infect humans, including H5N1, H5N2, H7N2, H7N3, H7N7, H9N2, H10N7, and H7N9. Among them, H5 has attracted much attention due to its high pathogenicity.
Mechanism of H5N1 Infection in Humans
Studies have found that humans are mainly infected by H1, H2, H3 and N1, N2 subtypes of avian influenza viruses. Influenza virus HA binding receptors lead to different hosts that it infects. Human influenza virus HA mainly binds to α-2,6 sialic acid receptors in human respiratory epithelial cells, avian influenza virus HA mainly binds to α-2,3 sialic acid receptors on avian intestinal tissue, and swine tracheal epithelial cells have both α-2,6 sialic acid receptors and α-2,3 sialic acid receptors. Due to the characteristics of influenza virus genome segments, influenza virus is prone to antigenic drift and antigenic conversion, resulting in the continuous generation of new subtypes of influenza virus. When humans are in direct contact with infected animals or H5N1 avian influenza viruses in polluted environments, they generally do not cause disease due to the characteristics of the receptors, nor do they form widespread transmission among humans, but if the virus passes Naturally adapted or acquired a gene from a human virus, it is possible to start spreading epidemics in the population. Alphavirus H3N2, which circulates in pigs, began circulating in the United States in 2011. In recent years, studies have shown that pigs can be infected with the H5N1 virus under natural conditions, suggesting that the virus has a potential threat to human public health, and may spread to each other at any time and cause a pandemic. Even though H5N1 cannot be transmitted directly to humans, its ability to infect humans due to its acquired mutations requires us to strengthen our attention and research on the virus. Through further research and exploration, more convenient and reliable detection kits and related vaccines to be developed for detection and prevention. This is an effective way to prevent viral infectious diseases.