What the latest bird flu outbreak could mean for humans

A dangerous and contagious avian influenza continues to spread through farmed poultry, wild birds and now mammalian populations. There’s still no sign the virus can spread between people, but experts are closely monitoring the outbreak.

“The recent spread to mammals needs to be closely monitored,” said World Health Organization director-general Dr. Tedros Adhanom Ghebreyesus, during a press conference. “At the moment, the WHO estimates the risk for humans to be low.”

What is causing this outbreak of bird flu?

This particular outbreak is caused by the H5N1 avian flu virus, which was first detected in China in 1996. In 2021, a new variant of this virus emerged and started spreading around the world. The virus began infecting chickens on poultry farms in the United States in February 2022.

What’s different about this outbreak?

The size, range and number of species affected by this outbreak is unprecedented, says Nichola Hill, a virologist at the University of Massachusetts Boston.

This is the deadliest outbreak of bird flu in US history, affecting nearly 60 million poultry. Wild birds in all 50 states have the virus. “It’s never been seen before in this number of different wild species,” says Hill. It also infects mammals: skunks, bears, seals, foxes, dolphins and animals of other species show up with the virus. “That’s not how bird flu should behave,” she says.

Most disturbingly, the virus emerged on a mink farm, where it appears to have spread between mink – not just from birds to individual mink. This type of mammal-to-mammal spread is new. “We had never seen that before,” says Hill.

Is there a danger to humans?

Mammal-to-mammal spread is worrying, but does not automatically mean that the virus will significantly affect the human population.

Humans can contract bird flu, but cases are still rare. They are usually seen in people who work closely with birds. One person in the United States was infected with the virus during this current outbreak and that person was responsible for the culling of sick poultry.

Although the virus may evolve to infect more mammals, it has not currently mutated in a way that could more easily infect humans.

“It still doesn’t hit that magical combination of mutations necessary to unlock efficient human transmission,” says Hill.

But it’s still important to monitor and contain the spread of H5N1 in other animal species, because each time it adapts to a new host there’s a chance these mutations will occur. “We roll the dice every time,” she says.

The Centers for Disease Control and Prevention says people should avoid contact with wild birds and people working with poultry should take precautions like wearing gloves and masks.