H5N1 bird flu has infected growing numbers of people worldwide in recent years, but this week saw something new: the first recorded human case of an H5N5 avian influenza virus. What is this virus and how concerned about it should we be?

In early November, a resident of Grays Harbor, a county on the south-west Pacific coast of Washington state about 100 miles from Seattle, became severely unwell with flu-like symptoms including high fever, respiratory distress and confusion.

They were admitted to hospital, and on November 14 officials confirmed that tests showed infection with an H5N5 avian influenza virus. The patient, an older adult with underlying conditions, was treated in hospital, but sadly they died on November 21.

This was the first reported human infection with an H5N5 influenza virus.

H5N5 influenza viruses are a type of avian influenza (bird flu) – an influenza A virus........

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