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H7N9 strain mutated from chicken flu virus

By Tim Sandle     Jan 22, 2015 in Science
Beijing - Scientists have demonstrated how changes in a flu virus common to Chinese poultry farms triggered the rise of the novel avian H7N9 influenza A virus that has sickened hundreds of people since 2013.
H7N9 influenza A is a bird flu strain (avian influenza) and one that is capable of infecting humans. In fact, the World Health Organization (WHO) has identified H7N9 as "...an unusually dangerous virus for humans." Many of the human cases of H7N9 appear to have a link to live bird markets.
Researchers have been studying a virus called H9N2 chicken virus. This particular virus triggers egg production to fall and it affects the immune system of chickens, leading them at risk to other infections.
By using advanced genetic screening and comparing H9N2 chicken virus samples collected between 1994 and 2013, the researchers have shown how the virus has evolved and how it has often remained one step ahead of anti-viral treatments. This has involved making note of the virus in both geographical location and over time.
The studies have also shown the role played by H9N2 in enhancing the virulence with the form of avian flu that can affect people – H7N9. Data suggests that the H9N2 infected chickens served as the mixing vessel where H9N2 viruses from migratory birds and domestic ducks swapped genes. With this the studies have shown that the H7N9 virus contains six genes from the H9N2.
Part of this may have been caused by a vaccine developed for H9N2. An unintended and dangerous consequence of the vaccine could have been to mutate, mix and swap genes. thus creating a deadlier form of H7N9 and one capable of infecting people. Vaccines can increase pressure for hemagglutinin mutations (part of the protein structure of the virus) that help the virus escape vaccine detection and cause infection. This is termed “antigenic drift.” Antigenic drift is a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites.
The new findings emphasize the importance of continued surveillance of flu viruses, especially those circulating on poultry farms. In the future, the researchers argue, examining H9N2 virus as a warning sign of emerging flu viruses will be of great importance.
The study was led by the China Agricultural University, Beijing. The findings have been reported to the journal Proceedings of the National Academy of Sciences. The paper is titled “Evolution of the H9N2 influenza genotype that facilitated the genesis of the novel H7N9 virus.”
More about Influenza, Flu, Chickens, Bird flu, Avian flu
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