A new bird flu mutation of H5N1 has been discovered in a patient in the US state of Louisiana. Public health officials are concerned the new strain may rapidly develop, increasing its ability to affect humans.

The CDC has confirmed a total of 66 human cases of bird flu across the United States as of Friday, although the number is believed to be higher.

The ongoing spread of bird flu in the United States has alarmed experts -- not just because of human cases causing severe illness, but also due to troubling new instances of infections in cats.