Bird flu can pass to mammals. Should we worry?

An uncomfortable truth is that another influenza pandemic is in mankind’s future. Whether it will be a relative of the deadly avian flu strain currently wreaking havoc on bird populations around the world is anyone’s guess.

Because the virus, called H5N1, can be deadly to birds, mammals and people, researchers closely monitor reports of new cases. Worryingly, a new variant of H5N1 that surfaced in 2020 has not only spread more than ever among the birdsbut has also spread to other animals, increasing the risk of human outbreaks (No: 12/12/22,

was associated with the version a seal dying in maine the last summer. In October, there was a H5N1 outbreak on a mink farm in SpainResearchers reported in January euro surveillance, (It is not clear how the mink were exposed, but the animals were fed poultry byproducts.) Sea lions off the coast of Peru and wild bears, foxes and skunks in the United States and Europe, which prey on the birds Or clean them. Tested positive for the virus.

Globally, millions of domestic fowl have been culled or died from the new strain. It’s also likely that millions of wild birds have died, although few government agencies are counting, says Michelle Wiley, a viral ecologist at the University of Sydney who studies avian influenza. “This virus is devastating to bird populations.”

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

What’s more, four of the reported human cases – including A US case from Colorado And Two workers associated with the Spanish mink farm — were in people who had no respiratory symptoms. This leaves open the possibility that those people were not actually infected. Instead, the tests may have picked up viral contamination, say in the nose, that people breathed in while handling infected birds.

The impossibility of predicting which avian influenza viruses might make the jump to people and spark an outbreak is partly related to knowledge gaps. These bird pathogens are generally not easily infected or transmitted between mammals, including humans. And scientists do not fully understand how these viruses may need to change for human transmission.

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

The good news is that flu drugs and vaccines that work against the virus already exist, Wiley says. Compared to the world when the coronavirus arrived on the back of the COVID-19 pandemic, “we’re 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 called highly pathogenic avian influenza, which is especially deadly to both domestic and wild birds. Water birds such as ducks naturally carry avian flu with no or mild symptoms of infection. But when influenza viruses shuffle between poultry and waterfowl, variants that make them lethal to birds can spread further.

Avian viruses can be serious or even fatal to people. Since 2003, there have been 873 human cases of H5N1 infection. reported to the World Health Organization, A little less than half of them died. In February, an 11-year-old girl in Cambodia died after developing severe pneumonia from the avian flu virus, the country’s first infection since 2014. Her father was also infected with the virus—a different type than the widespread outbreak in birds—though he did not develop symptoms. It is not known how the two people were exposed.

Much of what scientists know about the pandemic potential of H5N1 comes from Controversial research on ferrets done more than a decade ago (Sn: 6/21/13, Experiments have shown that some changes to a protein that helps the virus break down into cells and make more copies of itself may help the virus infect ferrets through the air, according to influenza research. In a common laboratory stand-in for humans.

While researchers know these mutations are important in lab settings, it’s still unclear how important these changes are in the real world, says pathologist and virologist Jonathan Runstaedler of Tufts University’s Cummings School of Veterinary Medicine in North Grafton, Mass. They say.

Viruses mutate constantly, but not all genetic variations work at the same time. One change may help one version of the virus to transmit better, while harming another version and making it less likely to spread.

“We’re not sure how important or how big the difference is or how much to worry about those mutations when they occur in the wild,” Runstaedler says. “Or when they are five years down the road when there are other changes in the genetic background of the virus that are affecting them.” [original] mutation.

That doesn’t stop researchers from trying to pinpoint specific changes. Runstaedler and his team look for viruses in nature that have jumped into new animals and work backwards to figure out which mutations were important. And virologist Lewis Moncla says his lab is trying to develop ways to scan the entire genetic blueprint of viruses from past outbreaks to look for signatures of viruses that can be found between different animal species. can jump.

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

For example, genetic analysis of H5N1 circulating on a mink farm in Spain revealed a change Viruses known to help 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. Mink-to-mink transmission could have occurred on the farm, the researchers concluded, but it is unclear how much of a role specific mutations played in the outbreak.

When influenza viruses with the potential to transmit between mammals can make the jump from birds, Runstaedler says, it’s a numbers game. “The more chance you give a virus to spread and adapt, the greater the risk that one of those adaptations will be dominant.” [at helping the virus spread among other animals] Or take root and become a real problem.

Ongoing outbreak still a major problem for birds

Despite our inability to predict the future of humans with H5N1, it is clear that many species of birds – and some of the other animals that feed on them – are now dying out. And more species of birds are dying in this outbreak than in previous ones, Culhane and Wiley say.

“We’ve seen huge outbreaks in raptors and seabirds, which were never really affected before,” says Wiley. It is possible that genetic changes may have helped the virus spread more efficiently among birds than previous versions of H5N1, but this is unknown. “There are a number of studies underway to try and figure this out,” Wiley says.

Historically, these deadly avian flus have not been a persistent problem in the US, Moncla says. Sporadic outbreaks of H5N1 variants are usually confined to parts of Asia, where the virus has spread among birds since emerging in the late 1990s, and in North Africa.

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

The latest variant of H5N1 reached North American shores from Europe in late 2021, first arriving in Newfoundland and Labrador in Canada. From there, it spread south into the United States, where millions of domestic chickens Farms where the virus has been detected have been selected to prevent transmission. By December 2022, the virus had made it to South America. in Peru, Thousands of pelicans and over 700 sea lions have been dead since mid-January.

It’s important to understand how nonavian animals are being exposed, says Culhane. The highly pathogenic Avian Influenza infects every organ in a bird’s body. So, a fox chewing on an infected bird is exposing its mouth, nose and stomach to a lot of virus as it eats its food.

For now, experts are keeping an eye on infected animals to sound the alarm early if H5N1 starts to spread among mammals.

“I think the mink outbreak, and then the sea lion outbreak, is a wake-up call,” Moncla says. “We must do our best to apply as much science as possible to try and understand what is happening with these viruses so that if the situation changes, we are better prepared.”