Ten months on from the shocking discovery that a virus usually carried by wild birds can readily infect cows, at least 68 people in North America have become ill from the pathogen and one person has died.
Although many of the infections have been mild, emerging data indicate that variants of the avian influenza virus H5N1 that are spreading in North America can cause severe disease and death, especially when passed directly to humans from birds. The virus is also adapting to new hosts — cows and other mammals — raising the risk that it could spark a human pandemic.