Avian Flu Transmission Among Humans Unlikely

According to a new study published in Science, the avian H7N9 influenza virus that emerged this year is not adapted for sustained human-to-human transmission. This finding suggests that the current form of the virus is unlikely to cause a pandemic.

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A total of 139 confirmed human cases (including 45 deaths) of avian H7N9 influenza have been reported by the WHO as of November 6^th. Most of these cases have been linked to infected poultry, but some may have been due to limited human-to-human transmission.

Scientists from The Scripps Research Institute (TSRI) examined the 3D structures of the hemagglutinin (HA) protein on the virus surface and its interaction with the human influenza receptor. 

Previous studies have shown that compared to influenza viruses that are adapted for spread among birds, viruses adapted to humans generally have different amino acids at the HA site that recognize and bind to the human receptor.

More recent research had also shown that certain H7N9 viruses had acquired mutations that might make them more adapted to humans. 

When X-ray crystallography was used to study the HA and receptor structures, it showed that the HA in avian H7N9 influenza most closely resembled that of viruses that spread easily among birds, and only weakly attached to human influenza receptors.

The study authors concluded that the H7N9 virus would need to go through multiple mutations for it to become transmissible from person-to-person.

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