Health officials said Monday that a patient in Louisiana with a severe case of bird flu has died, the first reported human death from the disease in the U.S.

The first person has died of bird flu in the United States, the Louisiana Department of Health confirmed on Monday. The patient, who was exposed to non-commercial backyard flock and wild birds, was over age 65 and had underlying medical conditions,

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.