H5N8 Avian Influenza: How likely is “human-to-human transmission”?

H5N8 Avian Influenza: How likely is “human-to-human transmission”?  After the first human-infected H5N8 bird flu was discovered in Russia, how likely is it to be transmitted from person to person in the future?

According to CCTV News, Anna Popova, director of the Russian Federation’s Consumer Rights Protection and Public Welfare Supervision Agency, stated on the 20th that 7 people in Russia have been diagnosed with H5N8 avian influenza virus. This is the first time that humans have been infected with the avian influenza virus in the world. .

Russian media quoted Popova as saying that in December last year, an avian influenza outbreak broke out in a farm in southern Russia. Experts from the Russian National Science Center for “Vector” Virology and Biotechnology isolated the virus from the seven employees of the farm. The genetic material of the virus.

Popova said that Russia has immediately taken relevant necessary measures and reported the relevant situation to the World Health Organization. Seven infected people have mild symptoms, and human-to-human transmission has not been found, but it is not ruled out that the virus will mutate and cause human-to-human transmission in the future.

01 Seven infected persons had mild symptoms and no human-to-human transmission was found

According to news from Chinanews.com on the 21st, according to Russian media reports, Popova said in the “Russia 24” TV program: “Today, I want to reveal the scientific research personnel of the “Vector” Science Center under the Russian Consumer Rights Protection and Public Welfare Supervision Bureau. An important scientific discovery: the first laboratory-confirmed human case of H5N8 avian influenza was found in Russia.”

Researchers isolated the genetic material of this flu from samples taken by seven employees of a poultry farm in southern Russia. This poultry farm broke out of avian influenza in December 2020. After that, various epidemic prevention measures were quickly taken.了控制。 The control.

Popova said: “All seven people I talked about are in good condition, with mild clinical symptoms.”

According to Science and Technology Daily, Anna Popova said that the H5N8 avian influenza virus found in these seven employees was relatively mild and had little harm. The virus did not develop further, and the patients felt good.

Popova said that the H5N8 avian influenza virus has overcome intermediate barriers and has been able to spread from birds to humans, but it has not been found that this virus can spread from person to person. It takes time to track and study whether the virus can overcome obstacles to spread from person to person after it mutates. She said that since the virus was discovered at an early stage, there is time to prepare for possible mutations; this virus may also spread from person to person in the future, so it is necessary to prepare test systems and vaccine development platforms in advance.

Popova said that a few days ago, Russia had sent the data of the first case of H5N8 influenza virus infection to the World Health Organization, and stored the whole genome sequence of the H5N8 virus in the international database GISAID.

02 What is the origin of H5N8?

Avian influenza virus (AIV), that is, viral influenza of poultry, is an infectious disease of poultry that causes a variety of symptoms from the respiratory system to severe systemic sepsis by influenza A virus. Avian influenza is easy to spread among birds. It was called “chicken plague” in the past.

After poultry are infected with AIV, some show mild clinical symptoms, some show respiratory diseases and decreased egg production, and serious ones can lead to systemic diseases, and the mortality rate can reach 100%.

The H5 subtype avian influenza virus is a highly pathogenic avian influenza virus. For example, H5N1 not only infects poultry, but also spreads from infected poultry to humans across species barriers, leading to a serious public health crisis. With the spread of H5 subtype avian influenza, its harm has attracted worldwide attention.

The highly pathogenic avian influenza H5N8 virus was first detected in poultry in China in 2010 and appeared in poultry in Korea and Japan in early 2014. At the end of 2014, the H5N8 virus has spread to Europe and North America. Because the H5N8 virus can spread rapidly between different regions and infect a variety of birds, once it is epidemic, it will cause serious economic losses to the poultry breeding industry.

According to OIE public data, since 2020, many countries around the world have successively experienced avian influenza epidemics. In 35 countries including Germany, Hungary, Denmark, Russia, the Netherlands, Vietnam, South Korea, Poland, and Japan, a total of 1,277 cases of avian influenza of various subtypes were reported, of which 691 were poultry avian influenza and 586 were Wild bird flu epidemic.

Among them, the H5N8 subtype avian influenza had the highest proportion, with 1061 cases, accounting for 83.09%. In recent months, many countries such as Europe, the Middle East, North Africa, Japan, South Korea, and China have successively reported H5N8 avian influenza, but as of Russia’s report on the 20th, it had only spread among poultry.

According to a reference report on November 30, 2020, an outbreak of H5N8 avian influenza occurred on a farm in North Yorkshire, England. The British government stated that tens of thousands of turkeys on the farm were “humanely culled” in order to control the spread of the disease. On February 1 this year, Beijing also notified that wild black swan in the Yuanmingyuan Ruins Park was infected with H5N8 avian influenza. The local area immediately carried out emergency treatment to disinfect the surrounding environment. All sick and dead wild birds have been treated harmlessly. The disease only occurs locally and has been effectively controlled.

03 What is the risk of person-to-person transmission?

On the 20th, Popova reported that human-to-human H5N8 infection was discovered for the first time, and said that 7 infected people had mild symptoms, and human-to-human transmission has not been found. It cannot be ruled out that the virus will mutate and cause human-to-human transmission in the future. For the time being, the situation seems to be under control.

Generally speaking, avian influenza is highly targeted at poultry and does not infect humans. This is because influenza viruses are species-specific, and humans have no receptors that avian influenza binds to. It’s like a key can only open a lock, your house key can’t open a neighbor’s door.

The vast majority of avian flu only spreads between poultry, and in rare cases it can infect pigs. Only in rare cases, bird flu can cross the species barrier to infect humans-such as the H7N9 bird flu epidemic in 2013.

H7N9 is a three-source reassortant virus, in which H7 comes from domestic ducks in the Yangtze River Delta and N9 comes from Korean migratory birds. It is a two-step reassortment from migratory birds to ducks to chickens. The H7N9 virus can only bind to receptors on the surface of avian cells, that is, it can only infect birds. However, in the evolution of nature, the 186th amino acid on the virus changed from glycine (G) to valine (V), allowing the virus to acquire the ability to bind to human receptors.

However, no matter what kind of influenza virus, in order to achieve effective human-to-human transmission, two conditions must be met at the same time:

1) Influenza virus can bind to human respiratory epithelial cells;
2) Influenza viruses can effectively multiply in the human respiratory tract.

To achieve these two points, the avian influenza virus needs to have corresponding genetic mutations, but these mutations have not been observed on H7N9, so H7N9 is difficult to spread through droplets like the new coronavirus. The result of the computer simulation is that under natural conditions, it would take more than ten years for H7N9 to fully acquire the ability of human-to-human transmission through genetic mutation.

Therefore, even if a small number of close contacts are found to be infected with H7N9, whether it is the Chinese health department or the WHO, the view of the avian influenza virus is still that it is not easy to spread from person to person. In 2013, more than 100 people were infected in China, most of which were sporadic cases. Facts have also proved that the ability of this virus to spread from person to person is indeed weak.

However, it is worth noting that H7N9 avian influenza is less pathogenic to poultry, but it has a certain probability of infection in humans. In fact, looking back at the past cases of H5 subtype of avian influenza, as highly pathogenic subtypes of avian influenza, N5N1 and H5N6 are both highly pathogenic subtypes of avian influenza that can infect humans. The related cases have more mild infections. Few, most of them are severely ill patients with rapid disease progression. Severe pneumonia usually occurs within 3 to 7 days after the onset of onset. Most of the body temperature continues to be above 39 ℃, breathing difficulties, and may be accompanied by hemoptysis, and the mortality rate is high.

After the wild black swan H5N8 avian influenza outbreak occurred in Beijing at the beginning of this year, the Chinese Center for Disease Control and Prevention reminded that humans should be prevented from contracting avian influenza.

04 Prevent human infection with avian influenza

According to Russian media reports on the 21st, Linate Makshutov, director of the Russian “Vector” National Virology and Biotechnology Science Center, said in a live broadcast recently: “The rapid deciphering of the highly pathogenic avian influenza virus makes us The development of a detection system can be started to detect infected persons in time and treat patients.” At the same time, the development of candidate vaccines for humans can also be initiated to deal with the H5N8 avian influenza virus.

The Chinese Center for Disease Control and Prevention reminds that the main source of human infection with bird flu is contact with infected live poultry or having been to a contaminated live poultry market. The initial stage of infection usually manifests as flu-like symptoms, such as fever, cough, and low sputum, which may be accompanied by headache, muscle aches and general malaise. The condition of severely ill patients develops rapidly, with symptoms such as severe pneumonia.

So, how should we prevent bird flu?

1. Try to avoid contact with live poultry or live poultry markets. If contact is necessary, personal protection should be strengthened, such as wearing masks and gloves, and washing hands with soap and water as soon as possible;

2. Do not buy live poultry, and encourage the purchase of chilled or chilled poultry that has been slaughtered and processed in a centralized manner;

3. Do not purchase live poultry from live poultry markets or mobile vendors, let alone mix with original poultry;

4. If you have fever and respiratory symptoms, you should wear a mask, see a doctor as soon as possible, and tell the doctor whether there is a history of contact with poultry or whether you have been to the live poultry market before the onset of illness.

(source:internet, reference only)

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