When, where and how the H5N1 bird flu virus may evolve and its capacity to spark a pandemic is hard to predict — in part, some researchers say, because of federal restrictions on gain-of-function research.

The first severe case of H5N1 bird flu was confirmed in Louisiana. Here is a map of other states that have been affected.

The presence of highly pathogenic avian influenza, or H5N1 bird flu, has been confirmed after officials worked to quarantine a backyard flock in Franklin County last week. HPAI was confirmed in the 24-bird flock by Vermont’s Agency of Agriculture,

The CDC has declared the first “severe” case of H5N1 bird flu in the U.S., according to a press release published Wednesday. The good news? The person who contracted the virus appears to have gotten it from backyard poultry,

Los Angeles County health officials have identified three more cats with presumptive H5N1; the source of the virus has not yet determined, but experts suspect raw meat.

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. A sample of the virus found in a critically ill patient in the United States has shown signs of mutating to better suit human airways,

The bird flu virus found in a severely ill patient hospitalized in the United States has mutated to become better adapted to human airways, though there is no evidence it