Human bird flu cases are increasing across the country. The H5N1 virus primarily infects poultry and mammals but can be transmitted to humans via direct contact with sick animals, per the Centers for Disease Control and Prevention (CDC).

Two months shy of the fifth anniversary of COVID-19 being declared a global pandemic, the US has recorded its first human death as a result of avian influenza H5N1 infection. The unidentified Louisiana man contracted the virus through contact with infected wild and domestic birds on his property

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.

Though the bird flu has spread across multiple states in cattle and other birds, infections in mammals remain low, according to the CDC.