Bird flu in US: What we know, what we don't

The U.S. is in the midst of a multistate outbreak of bird flu, with 1 in 5 commercial milk samples testing positive for genetic traces of the virus. But does the virus pose any threat to humans? Highly pathogenic avian influenza is an infectious viral illness that spreads primarily among wild and domestic birds. But the virus that causes bird flu can sometimes jump into animals, including dairy cows and, in some cases, humans. "Bird flu, or avian influenza, infects more than 100 species of wild birds, especially migratory waterfowl,"...