Bird flu can jump to mammals. Should we worry?

An uncomfortable truth is that there is another influenza pandemic in the future of humanity. No one knows if it will be a relative of the deadly strain of bird flu currently wreaking havoc on bird populations around the world.

Because the virus, called H5N1, can be deadly to birds, mammals and people, researchers are closely monitoring reports of new cases. Worryingly, a new variant of H5N1 that emerged in 2020 has not only spread farther than ever between birdsbut it has also spread to other animals, raising the specter of a human outbreak (Serial number: 12/12/22).

The variant was linked to a seal kill in Maine last summer. In October there was a H5N1 outbreak at a mink farm in Spainresearchers reported in January in Eurosurveillance. (It’s unclear how the minks were exposed, but the animals were fed poultry byproducts.) Sea lions off the coast of Peru and wild bears, foxes and skunks, which prey on or feed on birds, in the United States and Europe have also tested positive for the virus.

Globally, hundreds of millions of domestic poultry have been culled or have died from the new variant. Millions of wild birds are also likely to have died, though few government agencies are counting, says Michelle Wille, a viral ecologist at the University of Sydney who studies avian influenza. “This virus is catastrophic for bird populations.”

A few human cases have also been reported, although there is no evidence that the virus is spreading between people. Of seven cases, six people recovered and one person from China died. In February, health officials in China reported an eighth case in a woman whose current status is unknown.

In addition, four of the reported human cases, including an American case from Colorado and two workers linked to the Spanish mink farm — were in people who did not have any respiratory symptoms. That leaves open the possibility that those people were not actually infected. Instead, the tests may have detected viral contamination, say in the nose, that people inhaled while handling infected birds.

The inability to predict which avian influenza viruses might make the jump to people and trigger an outbreak is partly related to knowledge gaps. These bird pathogens do not normally readily infect or circulate among mammals, including humans. And scientists don’t have a full idea of ​​how these viruses might need to change for human transmission to occur.

For now, it’s encouraging that so few people have been infected amid such a large outbreak among birds and other animals, says Marie Culhane, an animal veterinarian at the University of Minnesota in St. Paul. Still, experts around the world are watching for any signs that the virus may be evolving to spread more easily between people.

The good news is that there are already flu drugs and vaccines that work against the virus, Wille says. Compared to where the world was when the coronavirus behind the COVID-19 pandemic appeared on the scene, “we are already ahead of the game”.

How the virus would have to change to spread between people is a big unknown

This new iteration of bird flu is what’s called highly pathogenic bird flu, which is particularly deadly to both domestic and wild birds. Waterfowl, such as ducks, naturally transmit bird flu with no or minor signs of infection. But when influenza viruses mix between poultry and waterfowl, variants with changes that make them deadly to birds can emerge and spread.

Avian viruses can be serious or even fatal to people. Since 2003, there have been 873 human cases of H5N1 infections. reported to the World Health Organization. A little less than half of those people died. In February, an 11-year-old girl in Cambodia died after developing severe pneumonia from the bird flu virus, the first reported infection in the country since 2014. Her father was also infected with the virus, a different variant of the virus. that is behind the widespread virus. she outbreak in birds, although she has not developed symptoms. It is unknown how the two people were exposed.

Some of what scientists know about the pandemic potential of H5N1 comes from controversial research on ferrets made over a decade ago (Serial number: 06/21/13). The experiments showed that some changes in the proteins that help the virus enter cells and make more copies of itself could help the virus travel through the air to infect ferrets, a common laboratory surrogate for humans in the influenza research.

While researchers know these mutations are important in laboratory settings, it’s not yet clear how crucial those changes are in the real world, says Jonathan Runstadler, a disease ecologist and virologist at Tufts University Cummings School of Veterinary Medicine. in North Grafton, Mass.

Viruses are constantly changing, but not all genetic adjustments work together. A change can help one version of the virus transmit better, while hurting another variant and making it less likely to spread.

“We’re not sure how critical or how big the difference is or how much we need to worry about those mutations when they occur in nature,” Runstadler says. “Or when they happen five years later, when there are other changes in the genetic background of the virus that affect those (original) mutations.”

That doesn’t stop researchers from trying to identify specific changes. Runstadler and her team search for viruses in the wild that have jumped to new animals and work backwards to discover which mutations were crucial. And virologist Louise Moncla says her lab is trying to develop ways to scan entire genetic blueprints of viruses from previous outbreaks to look for signatures of a virus that can jump between different animal species.

“There’s a lot we don’t know about avian influenza viruses and host switching,” says Moncla, of the University of Pennsylvania.

Genetic analyzes of the H5N1 circulating on the mink farm in Spain, for example, revealed a change known to help the virus infect mice and mammalian cells grown in the laboratory. Such a change could make it easier for the virus to spread among mammals, including people. There could have been mink-to-mink transmission on the farm, the researchers concluded, but it’s not yet clear what role that specific mutation played in the outbreak.

It’s a numbers game for when influenza viruses with the ability to spread between mammals can make the jump from birds, Runstadler says. “The more opportunities you give the virus to spread and adapt, the greater the risk that one of those adaptations will either be effective (in helping the virus spread among other animals) or take root and be a real problem.” .

The ongoing outbreak continues to be a huge problem for birds.

Regardless of our inability to forecast the future for humans with H5N1, it is clear that many bird species, and some other animals that eat them, are dying now. And more bird species are dying in this outbreak than in previous ones, Culhane and Wille say.

“We have seen large outbreaks in birds of prey and seabirds, which have never really been affected before,” says Wille. The genetic changes may have helped the virus spread more efficiently among birds than earlier versions of H5N1, but that is unknown. “There are a number of studies underway to try to figure it out,” says Wille.

Historically, these deadly bird flus have not been a persistent problem in the Americas, Moncla says. Sporadic outbreaks of H5N1 variants are generally confined to places like parts of Asia, where the virus has circulated in birds since its emergence in the late 1990s, and North Africa.

The last major bird flu outbreak in North America was in 2015, when experts detected more than 200 cases of a virus other than bird flu in commercial and backyard poultry in the United States. The poultry industry culled more than 45 million birds to stop the spread of that virus, Culhane says. “But it didn’t disappear from the rest of the world.”

The latest version of H5N1 washed up on North American shores from Europe in late 2021 and first appeared in Canada in Newfoundland and Labrador. From there, it spread to the southern United States, where until now tens of millions of domestic birds have been culled to prevent transmission on farms where the virus has been detected. By December 2022, the virus had reached South America. In Peru, tens of thousands of pelicans and more than 700 sea lions They have been dead since mid-January.

It’s important to understand exactly how animals other than birds are exposed, Culhane says. Highly pathogenic avian influenzas infect all organs of a bird’s body. Therefore, a fox that bites an infected bird exposes its own mouth, nose and stomach to a large amount of virus while eating its food.

For now, experts are keeping an eye on infected animals to raise the alarm early if H5N1 begins to spread between mammals.

“I think the mink outbreak, and then the sea lion outbreak, is a wake-up call,” says Moncla. “We should be doing everything we can to implement all the science we can to try to understand what is happening with these viruses so that if the situation changes, we are better prepared.”