Bird flu in China
What is behind the first case of infection with the H10N3 strain
Tatiana Pichugina, RIA Novosti
In the Chinese province of Jiangsu, the first case of human infection with the H10N3 strain of avian influenza virus has been identified. Previously, it was found only in wild waterfowl. However, scientists have warned about the risk of infection of mammals.
Who got infected and where
World media with reference to the State Committee on Health China reports that a 41-year-old resident of the city of Zhenjiang, hospitalized on April 28 with flu-like symptoms, was found to have a strain of H10N3 avian influenza virus.
The patient's condition is satisfactory, he is being prepared for discharge. The medics tracked down everyone he was in contact with, but they didn't notice anything alarming. Nothing is said about how the patient got infected, where the original source is.
The H10N3 strain was first identified in Hong Kong in 1979, then in 2011 at the bird market in Thailand. People have never had it fixed before.
The H10 subtype has been known among waterfowl in different regions of the world for more than half a century. In particular, it is found in wild birds in the Amur region. Strains infect birds, but some are pathogenic to humans.
Where does avian flu come from
The influenza virus belongs to the family of orthomyxoviruses. It spreads in the form of single-stranded, coiled RNAs in the lipid membrane. It is able to bypass the immune defense and penetrate into the cell with the help of spike proteins on the membrane.
There are seven types of influenza viruses, of which three – A, B and C – infect humans. Type A viruses, in turn, differ depending on the gene encoding the protein (glycoprotein) on the membrane. Neuraminidase is denoted by NA, gemmaglutinin – HA. The latter is divided into 18 subtypes: H1, H2 and so on.
Influenza A viruses cause outbreaks of infection in the animal world from time to time. Their natural reservoir is wild waterfowl, mainly goose– and plover-like (the most famous representative is sea gulls). Hence the name – bird flu. The virus is not dangerous for wild species, and some strains are deadly for domestic ones.
HA viruses are under evolutionary pressure and are able to overcome the interspecific barrier, including to penetrate into the human population. In 1918, the H1N1 strain, Spanish, claimed millions of lives. The last outbreak of avian influenza type A in 2016-17 was caused by the H7N9 strain. Before COVID-19, subtypes H5 and H7 were considered as the most likely source of a new pandemic, and even now they are not discounted.
The virus spreads by airborne droplets, infects the epithelial cells of the respiratory tract and begins to copy itself using other people's resources. The body reacts with high fever, fever, runny nose and other respiratory symptoms. The immune defense, recognizing a spike protein on the virus membrane (hemaglutinin), produces antibodies. There is no special treatment, the drugs only alleviate the disease and prevent complications, including pneumonia, autoimmune processes.
Influenza A virus strains are constantly circulating among people, they are included in the annual vaccines. However, the part of the virus genome encoding the spike protein evolves rapidly under the pressure of the body's immune system. New strains elude neutralizing antibodies, and the effectiveness of the vaccine decreases. And if a completely new strain overcomes the interspecific barrier from birds to humans, the available vaccines are completely useless.
How dangerous is the H10 subtype
The subtype of avian influenza H10 is detected mainly in wild birds. There are many strains of this subtype in China, but its effects on mammals are poorly understood. In 1984, the H10N7 strain was found in minks on farms in Sweden. In 2008 – in pigs. In 2014, seals died from it off the coast Denmark. People have been sick with this flu since 2004.
The H10N8 strain caused an epidemic in 2013-2014 in China. Sequencing showed that there are inserts from another subtype in his genome. The ability of H10 to reassemble RNA from other variants of viruses is extremely dangerous. This increases the risk of a highly pathogenic strain.
In a 2016 article in Nature, Chinese scientists showed that H10N3 infects mice and carries signs of contagion to humans. It was impossible to predict when it would spread to a person, and this happened. However, as Xinhua reports with reference to experts, the variant of the virus isolated from the patient is low-pathogenic, the risk of an epidemic is estimated as low.
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