Will human infection with avian influenza H5N8 virus cause the next pandemic?

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According to the host source, influenza A viruses can be classified into avian influenza, swine influenza or other animal influenza viruses, including A H5N1 and A H9N2 avian influenza virus subtypes and A H1N1 and H3N2 swine influenza virus subtypes.

Humans can be infected with avian influenza and other zoonotic influenza viruses.

Graphic source of avian influenza virus: Chinese Center for Disease Control and Prevention

H5N8 avian influenza has been found in birds before 1983, and an outbreak of H5N8 occurred in breeding ducks in Korea in 2014.

In the past six months, many cases have been reported in France, Germany, Italy, Spain, the United Kingdom, Japan, South Korea and my country.

The World Organization for Animal Health (OIE) stated in the latest situation regarding the recent epidemic that H5N8 influenza is considered to be pathogenic, and currently has various manifestations such as asymptomatic, subclinical symptoms and partial lethality.

On February 1 this year, my country’s Animal Disease Prevention and Control Center reported that the National Bird Flu Reference Laboratory confirmed that a wild swan H5N8 subtype highly pathogenic avian influenza epidemic occurred in the Yuanmingyuan Relics Park in Haidian District.

Previous studies have shown that H5N8 is highly pathogenic in chickens, but so far, its ability to induce significant clinical diseases in domestic ducks and ferrets is extremely poor, which may allow the virus to establish in these hosts.

In addition, the virus is only moderately pathogenic in mice, and its tissue trophicity is limited compared to the previous HPAI H5N1 virus.

Although these findings minimize the concern that the highly pathogenic avian influenza H5N8 virus can cause human infections with its current phenotype, there are signs that the virus may become endemic in livestock and poultry , This may change the genetic evolution of pre-existing virus strains.

In fact, as early as 2017, a study published in Virulence pointed out that although the pathogenicity of H5N8 virus in mammalian hosts is relatively low to moderate, researchers have replaced the PB2 gene fragment of H5N8 virus with H5N1 virus.

In other words, if the H5N1 virus and the H5N8 virus are in the same host and the genes are recombined and transformed, then its pathogenicity to mammals will increase 1000 times.

Pathogenicity of recombinant W452 reassortant virus carrying W149 fragment in mice: Virulence

Comparison of growth curves in MDCK, A549 and NHBE cells after parental and reassortant virus infection Source: Virulence

Further research and analysis showed that among all the viruses tested, the H5N8 virus containing the recombinant W149 gene fragment also induced the highest virus titer and the highest level of inflammatory cytokine response in the lungs at all time points, and this high virulence indicates The type was also confirmed by high viral titers in the respiratory tract of infected ferrets.

In addition, micro-genome analysis showed that W14 has significantly increased polymerase activity (p<0.

The results of various studies indicate that a single gene replacement from other avian influenza viruses can change the recent H5N8 virus which is highly pathogenic to mammals.

In the same year, the team at the Hudson Institute of Medical Research in Australia also confirmed this view.

This review, published in the same journal, stated that the widespread distribution of H5N8 and the genetic recombination of other circulating avian influenza viruses that have been observed against H5N8.

At the same time, it called for more research to deeply understand the pathogenicity of H5N8 virus in birds and mammals, as well as its potential ability to reanalyze or adapt to humans, and remind patients to develop effective treatments for severe "avian flu" patients.
method.

Image source: Virulence

Although Russia is now the only country where the virus has been identified in humans, there have been reports of H5N8 outbreaks in poultry throughout Europe.

In December last year, in response to the spread of H5N8 avian influenza in birds around the world, Dr.
Alex Berezow of the American Council of Science and Health even questioned whether H5N8 would be the next pandemic?

Source: acsh.
org

An important reason why influenza constitutes a continuous pandemic threat is its ability to mutate rapidly.

The virus not only mutates during reproduction, but also recombines with other influenza viruses.
For example, if two different influenza viruses infect the same person or animal, the viruses can exchange genes to form a completely new virus.

In 1918, the "Spanish influenza" pandemic caused by the H1N1 influenza virus was estimated to have more than 500 million patients worldwide, with an incidence rate of about 40%, resulting in about 50 million deaths; in 1957, the "Asian influenza" caused by H2N2 "Causing 1 million to 2 million deaths worldwide; in 1968, H2N2 virus and H3 poultry-derived virus reassorted, forming a new type of H3N2 virus that caused 500,000 to 1 million deaths worldwide.

It is worth mentioning that the influenza viruses of the 1957 and 1968 pandemics were produced by the recombination of viruses.
Fragments of the 1918 influenza virus were found in both viruses.

According to Ivette Nu? of the Center for Vaccines and Immunology at the University of Georgia? Professor ez and Ted Ross wrote a review for Ther Adv Vaccines Immunother magazine that the prevalence of H5 virus is increasing.

The good news is that H5 influenza is not easy to infect humans, but once the H5 virus infects humans, it will be highly lethal.

The author reports that as of July 2018, there were 860 human cases of H5 influenza infection and 454 deaths.

Most of these infections may be caused by human contact with infected birds (such as chickens), because human-to-human transmission is not common for the H5 virus.

The more frightening situation is that if the avian H5 virus infects a pig, and this pig is also infected with an influenza virus that is highly adapted to humans, such as the H3N2 and H1N1 viruses that cause seasonal influenza.

So, as mentioned above, gene shuffling will cause a new virus to pop out of pigs, which may then lead to a pandemic.

Source of infection process: Virulence

Previously, Hongjie Yu’s team from the School of Public Health of Fudan University, in collaboration with the China Center for Disease Control and the University of Hong Kong, published the title: Influenza-associated excess respiratory mortality in China, 2010-15 in The Lancet Public Health.
: A population-based study, the study showed that during the five years from 2010 to 2015, there were an average of 88,100 flu-related excess respiratory deaths in the country each year, accounting for 8.
2% of all respiratory deaths.
Elderly people over 60 accounted for flu-related deaths.
80% of deaths from excessive breathing.

Influenza virus infection may not only cause respiratory-related deaths, but may also cause deaths by triggering or exacerbating underlying chronic diseases (such as cardiovascular disease).
This research provides important information for optimizing future public health policies and interventions.

Source: Lancet Public Health

We must know that in our country, influenza vaccine has not yet been included in the national immunization plan.
In the past 15 years, the coverage rate of influenza vaccine has gradually increased, but it has only covered about 2% of the population.

In addition, China has a vast territory and the influenza virus activity varies greatly among provinces.
The northern provinces end up in winter, while the southern provinces end up in spring and summer.

According to WHO, it is impossible to eradicate influenza virus because many of its hidden hosts are waterfowl, and most of them cause asymptomatic or mild infections in birds.
The range of symptoms depends on the characteristics of the virus.
Human infections with zoonotic influenza will continue to occur.

The pandemic of the new crown epidemic has greatly deepened everyone's understanding of anti-virus.
Wearing masks in public places has become a habit for many people, which will greatly benefit influenza prevention and control.

It is not known whether the currently circulating avian influenza and other zoonotic influenza viruses will cause pandemics in the future.

However, there are many types of avian influenza and other zoonotic influenza viruses that cause human infections.
It is necessary to continuously monitor animal and human populations, conduct detailed investigations of each human infection case, and formulate a risk-based pandemic response plan.