Bird flu can jump to mammals. Should we care?

The inconvenient truth is that another influenza pandemic is in the human future. Whether it will be related to the deadly avian flu now wreaking havoc on bird populations around the world is anyone’s guess.

Because the virus, called H5N1, can be deadly to birds, mammals and humans, researchers are closely monitoring new cases. Worryingly, the new H5N1 variant that emerged in 2020 is not only spreading more widely than ever before in birds, but is also spreading to other animals, raising the specter of a human outbreak.SN: 12/12/22).

The variant was linked to a seal die-off in Maine last summer. In October, an outbreak of H5N1 occurred on a mink farm in Spain, researchers reported in January Eurosurveillance. (It is unclear how they were exposed to the credit, but the animals are fed chicken products.) There are sea lions off the coast of Peru and wild bears, foxes and skunks, which are taken by birds or boats, also in the United States and Europe. tested positive for the virus.

Globally, hundreds of millions of domestic chickens have been eliminated or died from the new variants. It’s also likely that millions of birds died, although few government agencies count, says Michelle Wille, a viral ecologist at the University of Sydney who studies avian influenza. “This virus is very destructive for the bird population.”

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

Five of the four reported human cases — including a US case from Colorado and two workers linked to a farm believed to be Spanish — were in people who did not have respiratory symptoms. That leaves the possibility that those people are truly infected. Instead, the tests picked up viral contamination, say in the noses, that people breathed in while handling the infected birds.

The impossibility of predicting which avian influenza virus might make the jump to humans and spark an outbreak is partly due to knowledge gaps. These pathogens do not easily infect birds or circulate between humans and typically do not infect mammals. And scientists don’t fully understand how these viruses need to mutate for human transmission to occur.

For now, it’s encouraging that so few people are infected amid so many outbreaks among birds and other animals, says Marie Culhane, a food animal veterinarian at the University of Minnesota in St. Paul. Even so, experts around the globe are watching carefully for any signs that the virus may be developing more easily among people.

The good news is that drugs and vaccines against the virus already exist, Wille says. Compared to where the world was when the coronavirus hit after the COVID-19 pandemic, “we’re already ahead of the game.”

How the virus needs to change in order to spread among humans is a big unknown

This new iteration of bird flu is called a highly pathogenic avian influenza, which is particularly lethal to domestic and wild birds. Waterfowl such as ducks naturally carry avian influenza with no or minor signs of infection. But when influenza viruses mix between chicken and fowl, variants with lethal mutations can emerge and spread to the birds.

Avian viruses can be serious or even fatal to humans. Since 2003, human cases of H5N1 infections have been 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 contracting severe pneumonia from an avian virus, the country’s first reported infection since 2014. Her father was also infected with the virus – the second variant after a widespread outbreak. disturbance in the birds – although the symptoms did not develop. It is unknown how the two men were exposed.

Some of what scientists know about the pandemic potential of H5N1 comes from controversial research on ferrets more than a decade ago (SN: 6/21/13). Experiments have shown that changes in some proteins that help the virus break into cells and more copies of it can help the virus travel through the air to infect ferrets, a common laboratory-influenza research in humans.

While researchers know these changes are important in lab settings, it’s still unclear how significant those changes are in the real world, says Jonathan Runstadler, a disease ecologist and virologist at Tufts University’s Cummings School of Medicine in North Grafton, Mass.

Viruses are constantly changing, but not all genetic tweaks work together. A mutation can help pass on one version of the virus that is better, while also harming another variant and making it less likely.

“We’re not sure how critical or how big the difference is or how concerned about those changes when they happen in the wild,” says Runstadler. “Or when they happen five years down the road when other changes in the genetic background of the virus are impacting them. [original] changes “

It does not stop researchers from trying to identify specific changes. Runstadler and his team are looking for viruses in nature that jumped into the new animals and are working backwards to figure out which of the changes were crucial. And virologist Louise Moncla says her lab is trying to develop methods to scan the entire genetic blueprint of a virus from past movements to look for signatures of a virus that can jump between different animal species.

“There’s a ton we don’t know about avian influenza viruses and their changing hosts,” says Moncla, of the University of Pennsylvania.

Genetic analyzes of H5N1 in a farm believed to be circulating in Spain, for example, revealed a characteristic mutation that helps the virus infect mice and mammalian cells grown in the lab. Such a change could make it easier for the virus to spread among mammals, including humans. The transmission of credit-to-mink farming may have occurred, the researchers concluded, but it is unclear how much of a role that specific mutation played in the outbreak.

It’s a numbers game when it comes to influenza viruses with the ability to transmit between mammals to make the jump from birds, Runstadler says. “The more chances you give the virus to shed and adapt, the higher the risk that one of those adaptations will be made. [at helping the virus spread among other animals] or remove the root and be the real problem.

The ongoing unrest is still a big problem for birds

Given our human inability to predict the future with H5N1, it’s clear that many species of birds — and some other animals that eat them — are dying now. More bird species are dying in this upheaval than in previous ones, Culhane and Wille say.

“We’ve seen massive disruptions in raptors and seabirds that have never been affected before,” Wille said. It’s possible that the genetic changes made the virus spread more efficiently in birds than earlier versions of H5N1, but it’s unknown. “There are many studies available to try and prove,” Wille said.

Historically, this deadly virus has not been a persistent problem in the Americas, Moncla says. Outbreaks of the H5N1 variant are typically limited to places like parts of Asia, where the virus has been circulating in birds since its emergence in the early 1990s, and in northern Africa.

The last major outbreak in North America was in 2015, when experts detected more than 200 different cases of bird flu in commercial and backyard chickens across the United States. The poultry industry has culled more than 45 million birds to stop the spread of the virus, Culhane says. “But he is not gone from the rest of the world.”

The latest version of H5N1 to reach North American shores from Europe in late 2021 first appeared in Canada in Newfoundland and Labrador. From there it spread south to the United States, where only tens of thousands of domestic chickens were culled to prevent the transmission of the virus on farms. In December 2022, the virus had made it to South America. In Peru, ten thousand pelicans and more than 700 sea lions have died since mid-January.

It is important to firstly understand how animals are not exposed to birds, says Culhane. Many pathogenic avian influenzas infect every organ of the bird’s body. So the fox, by chowing down on the infected bird, exposes its mouth, nose, and stomach to much of the virus, and eats its food.

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

“I think the commotion, and then the commotion of the sea lion, they call the police,” Moncla said. “We must do our best to implement all the knowledge, experience and understanding of what these viruses are doing so that if things change, we are better prepared.”