Bird flu has ‘mutated’ and may spread easier among humans via coughing after two severe cases detected

H5N1 bird flu from an extreme case in the US has mutated to attach to human upper airway cells, health chiefs have warned.

The case, spotted this month in a hospitalised Louisiana man, is the first “severe” bird flu case in the US amid its rapid spread through cows this year.

In nearby Canada, a healthy teenage boy was admitted to intensive care after contracting the same strain in October.

The new US case...