With so much H5N1 circulating in the U.S., scientists worry we are a few mutations away from a potential human pandemic.

Two cats that belonged to Michigan dairy workers died after being infected with bird flu. But it's still not clear how the animals got sick or whether they spread the virus to people in the household,

A CDC study has found H5N1 bird flu antibodies in veterinarians who had no symptoms and no knowledge they had been working with infected livestock.