A person in Louisiana who became severely ill with a bird flu virus known as H5N1 in December has passed away from the infection, marking the first known bird flu death in the US

The first person to have a severe case of H5N1 bird flu in the United States has died, according to the Louisiana Department of Health.

For influenza viruses, imperfection is a strength. They constantly mutate, producing new strains that challenge immune systems primed to fight earlier varieties. That’s what makes flu a life-long threat to humans and the animal species — mainly birds — that are vulnerable to it.