Avian flu is infecting cows across the US via cow-to-cow transmission. Here's what you need to know about the bird flu spread.

A strain of bird flu known as H5N1 or highly pathogenic avian influenza has made a worrying leap to cattle herds across the US over the past month. This development has sparked “enormous concern” among health experts, including the World Health Organization’s (WHO) chief scientist, who warned of the virus’ “extremely high” mortality rate in humans.