Is a bird flu pandemic next?

On Jan. 6, federal officials reported the first death of a U.S. resident from bird flu. Health officials had previously determined the virus, which typically affects animals, may have mutated after the Louisiana patient caught a strain from backyard poultry. Although the patient had underlying health conditions, the death raised questions about whether bird flu poses a growing threat to humans.

Where did bird flu come from? Avian influenza, known scientifically as H5N1, is a viral infection originating in wild aquatic birds like ducks and gulls. While “fowl plague” was observed in Italy during the late 1800s, the H5N1 strain was first detected in China in 1996. Since then, the virus has spread to 108 countries across five continents.

How does it spread? The virus likely first traveled by the migration of wild birds, passing from them to domesticated poultry such as chickens. But Benjamin Anderson, an epidemiologist at the University of Florida, said the flu’s behavior changed about three years ago, when genomic sequence data showed the virus had moved beyond birds and “started to gain some ability … that allows it to more easily infect mammalian species.”

Which animals have contracted the virus? Since 2022, the U.S. Department of Agriculture has identified the H5N1 strain in more than 200 types of mammals. During a multistate outbreak last March, cows contracted the virus for the first time. Over 900 herds in 16 states have now been affected. These animals usually catch the virus by coming into contact with dead birds or exposure to infected saliva, mucus, or feces.

How does the virus affect birds? Many water fowls carrying the pathogen do not show apparent symptoms. But it’s usually lethal for backyard flocks like chickens. Since 2022, more than 120 million U.S. aquatic birds and commercial poultry have either succumbed to sickness or been culled because of infection, helping drive egg prices up 150% in the past year. Although mortality rates among commercial birds are alarming at the local level, specifically for hard-hit states like California, experts believe the nationwide poultry industry will bounce back.

Is it lethal for cattle? About 98% of cows survive infection, according to the American Veterinary Medical Association. Thanks to pasteurization of dairy products, cows that test positive for bird flu do not have to be culled.

How does the virus affect humans? In people, the virus acts like typical influenza with symptoms such as fever, runny nose, and muscle aches. Health officials confirmed at least 66 people in the U.S. became infected with the virus last year, mostly from contact with infected cows. Globally, 142 people have died since 2003.

Should we be concerned about a human outbreak? The virus still doesn’t pass easily to humans, and while cow-to-cow transmission has been observed, researchers haven’t yet noticed the virus passing from person to person. Anderson emphasized that, in the latest case, the virus only mutated after the Louisiana patient contracted it, not before. So the case doesn’t necessarily suggest a more virulent strain is circulating. Still, Anderson believes the virus is getting stronger because a growing number of species are becoming infected at higher rates. While a bird flu pandemic may not be on the immediate horizon, the probability isn’t zero. “It’s a low risk right now,” said Anderson. “But the future risk is higher than it was two to three years ago.”