April 26

The National Health Commission issued a notice

A case of human infection with H3N8 avian influenza found in Henan Province

CDC tests patient specimens

The result is H3N8 avian influenza virus positive

Preliminary assessment by experts

The H3N8 avian influenza virus is of avian origin

Not yet have the ability to effectively infect people

So

What kind of virus is H3N8?

How is it spread?

How to prevent it?

Today, let’s learn about it for you

What are the classifications of influenza viruses?

Influenza virus belongs to the family Orthomyxoviridae and is a kind of RNA virus. According to the difference of virus matrix protein and nucleoprotein, it can be divided into four types: A, B, C and D. Among them, A, B and C influenza viruses can infect In humans, influenza D only infects pigs and cattle.

Influenza A viruses evolve the fastest and have the highest fatality rate, often causing influenza pandemics in the world.

What kind of virus is H3N8?

The surface of influenza virus is coated with a lipid layer, and the envelope is covered with glycoproteins composed of hemagglutinin (HA) and neuraminidase (NA), which are antigenic and determine the subtype of influenza virus.

Influenza A virus can be further divided into 18 HA subtypes (H1-H18) and 11 NA subtypes (N1-N11) according to the difference in antigenicity of HA and NA proteins on influenza A virus.

All strains of influenza A virus have been isolated from wild birds, while the H1, H2, H3, N1 and N2 subtypes are currently the most common in humans.

The H3N8 subtype influenza virus is the most common subtype in wild birds.

How does the H3N8 subtype influenza virus spread?

Factors such as the migration behavior of migratory birds, the feeding behavior of birds, and whether resident birds (poultry) are infected are all related to the spread of avian influenza virus.

The transmission route of waterfowl such as waterfowl is mainly fecal-oral route;

Transmission between poultry can occur via the fecal-oral route and the respiratory route;

It can be transmitted between mammals through droplets, aerosols, nasal secretions and other routes.

Under what circumstances does avian influenza virus infect humans?

The spread of influenza virus is affected by the environment, air humidity, temperature, air droplets, etc. Human cases of avian influenza infection usually have a history of contact with poultry or wild birds.

The key to whether the influenza virus can infect the host is whether the HA protein of the influenza virus can bind to the receptor on the surface of the host cell.

Influenza A viruses generally tend to bind to alpha-2,3 receptors, while only a small number of ciliated cells in the human upper respiratory tract express alpha-2,3 receptors, and the vast majority of non-ciliated cells express alpha-2,6 receptors , but the epithelium of the lower respiratory tract, cornea, conjunctiva, and lacrimal gland express α-2,3 receptors, which may be the main factor for the cross-species infection of avian influenza virus in humans.

However, cross-host infection must break through the host’s immune barrier, and innate immunity, humoral immunity, and cellular immunity can all limit influenza virus infection.

In addition, various proteins such as HA and NA need to evolve under immune selection pressure and other pressures, and major changes in phenotype may occur before the virulence of influenza virus can be changed or the host range can break through the human barrier.

Can H3N8 cause disease in humans?

The H3N8 subtype influenza has a wide range of hosts and can infect wild birds, poultry, horses, pigs, dogs, donkeys, cats, seals, camels and other mammals, and can cause cross-species transmission.

In 2021, it was reported that a new variant strain of H3N8 influenza virus XJ47 was isolated in Xinjiang from a wild duck originating from the East Africa-West Asia migration line. The virus strain mutated at several important receptor binding sites. It has the ability to infect mammals, and it is speculated that it may also have the potential to infect humans across species, suggesting that H3 subtype avian influenza viruses should be paid attention to.

In the case of human infection with H3N8 avian influenza reported this time, the H3N8 virus has evolved the ability to carry out cross-species transmission, but no further risk of large-scale transmission has been found so far.

How to prevent avian influenza virus infection?

1. Avoid contact with live poultry, and do not catch, raise and eat wild birds;
2. Poultry practitioners should do personal protection, wear masks, wash hands frequently, and have regular physical examinations;
3. Pay attention to food hygiene, raw and cooked food should be strictly separated;
4. Improve self-protection awareness. If you have a history of contact with poultry and are accompanied by respiratory symptoms, you should wear a mask and seek medical treatment immediately.

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