What is avian influenza?
Influenza virus belongs to orthomyxoviridae. According to its nuclear protein and matrix protein, it can be divided into three types: A, B, C and D. Influenza A virus infects humans and many different animals. Influenza B virus only spreads from person to person and causes seasonal epidemic. Type C is sporadic infection, and type D influenza virus mainly infects pigs and cattle. No human infection has been found.
According to the host source, influenza A virus can be divided into avian influenza, swine influenza or other animal influenza viruses. A tends to be zoonotic, and its natural host is considered as waterfowl. According to the antigenicity of two virus glycoproteins, influenza A virus can be divided into different subtypes: hemagglutinin and neuraminidase; Most HA-NA combinations in avian influenza viruses have been confirmed.
Avian influenza virus evolved through two main mechanisms: genetic drift by point mutation and genetic exchange by fragment genome recombination. These two mechanisms can endow avian influenza virus with new genetic characteristics, which may affect its transmission, pathogenicity and even antigenicity.
Humans may be infected with avian influenza and other zoonotic influenza viruses. The main route of infection is direct contact with infected animals or polluted environment, but all these animal influenza viruses are different from human influenza viruses and are not easy to spread effectively from person to person.
The history of influenza discovery
Since 1878, there have been many suspected highly pathogenic avian influenza virus outbreaks around the world. The highly pathogenic avian influenza outbreak in Scotland 1959 was confirmed as subtype A H5N 1. H5N 1 and its recombinant gene have been found to have caused thousands of outbreaks of farmed poultry and wild birds worldwide, and caused a large number of deaths.
H5Ny highly pathogenic avian influenza is fatal to most farmed poultry. Once found, it is usually slaughtered to prevent further spread. Some H5Ny highly pathogenic avian influenza have the potential of zoonosis and epidemic situation, because they can cross the species barrier and spread to mammals including humans.
At the same time, the continuous evolution of H5Ny avian influenza and its potential recombination with other subtypes of avian influenza obviously deserve close attention. Among H5Ny highly pathogenic avian influenza, H5N8 avian influenza is the most frequent outbreak in recent years.
Highly pathogenic H5N8 avian influenza was found in birds before 1983, and the H5N8 epidemic broke out in Korean breeding ducks in 20 14. In the past year, H5N8 avian influenza continued to break out among poultry in some countries in South Africa.
In addition, from June to June 2020, H5N8 avian influenza also caused many outbreaks in Central and Eastern Europe. The affected geographical areas are constantly expanding. In autumn and winter that year, H5N8 avian influenza broke out in Eurasia. In August of the same year, H5N8 avian influenza broke out in Russian poultry and wild birds, and the epidemic area expanded to Kazakhstan in mid-September. In June 5438+ 10, several European countries, including Denmark, Germany, Ireland, the Netherlands and the United Kingdom, reported a new wave of H5N8 outbreaks among poultry and wild birds. Since then, H5N8 avian influenza has broken out in the Middle East and East Asia. So far, at least 46 countries have reported highly pathogenic H5N8 avian influenza.
Until February of this year 1, China Center for Animal Disease Prevention and Control reported that a highly pathogenic avian influenza epidemic of wild swan H5N8 subtype occurred in Yuanmingyuan Ruins Park in Haidian District, which was confirmed by the National Avian Influenza Reference Laboratory.
In fact, in the past, H5N8 influenza virus was only found in poultry, but according to the WHO report, the first case of human infection with H5N8 influenza virus was reported in Russia from June 5438 to February last year. Seven poultry farm workers were positive for H5N8 avian influenza. As soon as the news came out, the global spread of avian influenza, especially H5N8 subtype, has become a major problem in poultry breeding and wildlife safety, and has also become a public health problem for all mankind.
Why does it cause human infection?
It can be seen from the above outbreak characteristics that although H5N8 virus has been frequently erupting in poultry, it is not easy to infect humans. So why is there a case of H5N8 avian influenza virus spreading from poultry to humans in Russia?
According to Ivetnu of the Center for Vaccine and Immunology at the University of Georgia? The review entitled "AreviewofH5nxavianilinflenzavirous" written by Professor ez and TedRoss for TherAdvVaccinesImmunother magazine may give us some explanations.
In fact, just like the coronavirus pneumonia-19 virus, the avian influenza virus will mutate during its reproduction, and it can recombine with other influenza viruses. For example, if two different influenza viruses infect the same person or animal, these viruses can exchange genes to form a brand-new virus.
For example, as shown in the figure below, the H5 virus of poultry infects a pig, and this pig is also infected with a seasonal influenza virus H3N2/H 1N 1 which is highly adaptable to humans. Then, the shuffling of virus genes will lead to the synthesis of a brand-new virus in pigs, and then infect susceptible people, which is very likely to lead to an epidemic.
What will happen to the virus mutation?
In 20 17, a study published in Virulence by the team of the Center for Research on Zoonomatous Infectious Diseases of Chungbuk National University in Korea pointed out that although the pathogenicity of H5N8 virus in mammalian hosts is relatively low to moderate, H5N 1 virus and H5N8 virus are in the same host, and their genes are recombined and transformed, so their pathogenicity to mammals will increase/kloc-.
In the same year, Professor Tate from the Department of Molecular and Translational Sciences of Monash University in Australia published a review in the same journal, saying that the widespread distribution of H5N8 and the observed gene recombination of other popular avian influenza viruses against H5N8 can make H5N8 virus adapt to the growth of human lung cells, and that there is a potential risk of human infection with H5N8 cases. At the same time, it also calls for more research to deeply understand the pathogenicity of H5N8 virus in birds and mammals and its potential reanalysis or adaptability to humans, so as to remind patients with severe "avian influenza" to formulate effective treatment methods.
What should I do in the face of the growing bird flu?
Due to the epidemic situation of coronavirus pneumonia-19, the prevention and control measures such as reducing mobility, increasing the use of masks, strengthening social distance and disinfection have reduced the incidence of seasonal influenza A and B viruses around the world. However, due to the long-distance migration of wild birds, the innate recombination ability of avian influenza virus, the enhancement of human receptor binding ability, the constant variation of antigenicity of highly pathogenic avian influenza and the epidemic trend, avian influenza virus has to be prevented.
According to WHO, because many hidden hosts of avian influenza virus are waterfowl, most of them will cause asymptomatic or mild infection in birds, so the virus cannot be eliminated, that is, the virus will coexist with human beings for a long time, and human infections will continue to occur.
It is imperative not to ignore the global spread of H5N8 avian influenza virus and its potential risks to poultry breeding, poultry wildlife and global public health. You know, in China, influenza vaccine has not been included in the national immunization program. In the past 15 years, the coverage rate of influenza vaccine has gradually increased, but it only covers about 2% of the population.
Therefore, the monitoring of highly pathogenic avian influenza in poultry farms and wild birds should be restored to the level before the coronavirus pneumonia-19 epidemic or higher. 2.3.4.4 The transmissibility, pathogenicity and antigenicity of BH5N8 need to be further evaluated. If there is obvious antigen variation, the vaccine should be updated according to the emerging highly pathogenic avian influenza.
In addition, education and publicity are also important, including strengthening personal protective measures, staying away from wild birds, and avoiding hunting and eating wild birds during the flu season. It is necessary to continuously monitor animal and human groups, make a detailed investigation of each human infection case, and make a risk-based influenza response plan.
References:
2. 3. 4. 4 Swan in Xinjiang, west of China, 2020, doi:10.3201/eid2612.201
7. People are infected with influenza A virus-Russian Federation, CSR/don/26-feb-202 1- influenza A-Russian Federation /en/