One of the earliest strains of bird flu isolated from a human in Texas shows a unique constellation of mutations that enable it to more easily replicate in human cells and cause more severe disease in mice compared to a strain found in dairy cattle,

With reports of the first human death from bird flu in the US, some Americans are feeling an uncomfortable flashback to the early days of Covid-19, when infectious disease experts were talking about a new virus that was sending people to the hospital with respiratory infections.

The first human death caused by H5N1 in the U.S. was reported in Louisiana on Jan. 6. Here's what to know about bird flu.