Mammals can contract bird flu. Are we to be worried?


The unpleasant truth is that humanity faces the prospect of another influenza pandemic. It is unknown whether it will be a relative of the deadly avian flu strain that is currently ravaging bird populations worldwide.

Researchers closely follow reports of new cases of the virus, which is known as H5N1, because it can kill people, birds, and mammals. Worrisomely, a new H5N1 variant that emerged in 2020 has not only spread farther than it has in the past among birds, but it has also spread to other animals, raising the possibility of an outbreak affecting humans (SN: 12/12/22).

The variant was linked to the summer seal extinction in Maine. According to a report published in Eurosurveillance in January, an H5N1 outbreak occurred on a mink farm in Spain in October. ( The mink were fed poultry by-products, but how they were exposed is unknown.) Wild bears, foxes, and skunks, which prey on or scavenge birds in the United States and Europe, as well as sea lions off the Peruvian coast, have all tested positive for the virus.

The new variant has been responsible for the deaths or culturing of hundreds of millions of domestic poultry worldwide. Michelle Wille, a viral ecologist at the University of Sydney who studies avian influenza, says that it is also likely that millions of wild birds have died, though few government agencies are counting. Bird populations are devastated by this virus.

There have also been a few human cases, but there is no evidence that the virus is spreading to people. Six of the seven cases were resolved, and one person from China perished. China’s health officials reported an eighth case in February, this time involving an unidentified woman.

Furthermore, four of the detailed human cases — including a U.S. case from Colorado and two laborers connected to the Spanish mink ranch — were in individuals who had no respiratory side effects. That raises the question of whether or not those individuals were actually infected. Instead, people may have breathed in viral contamination while handling infected birds, for example through their noses.

Knowledge gaps are one reason why it is impossible to predict which avian influenza viruses will infect humans and cause an outbreak. Most of the time, these pathogens from birds don’t easily spread to humans or other mammals. Additionally, scientists lack a complete understanding of the modifications that these viruses might require in order to transmit to humans.

According to Marie Culhane, a food animal veterinarian at the University of Minnesota in St. Paul, the fact that so few people have contracted the disease in the midst of such a widespread outbreak among birds and other animals is encouraging for the time being. Still, experts from all over the world are keeping a close eye out for any indications that the virus might be evolving to make it easier for people to spread it.

According to Wille, the good news is that vaccines and medications against the flu already exist. “We are already ahead of the game” in comparison to where the world was when the COVID-19 pandemic’s coronavirus emerged.

This new type of bird flu is known as a highly pathogenic avian influenza, and it is particularly lethal for both domestic and wild birds. It is unknown how the virus would need to change to spread to humans. Aquatic birds like ducks naturally carry avian flus that don’t cause any symptoms at all. However, when influenza viruses move between waterfowl and poultry, variants with modifications that render them fatal to birds may emerge and spread.

People can be seriously harmed or even killed by avian viruses. 873 human H5N1 infections have been reported to the World Health Organization since 2003. About half of those people passed away. Cambodia’s first reported avian flu infection since 2014 resulted in the death of an 11-year-old girl in February from severe pneumonia. Her father was also infected with the virus, but he did not show any symptoms because he had a different strain than the one that caused the widespread bird flu outbreak. How the two people were exposed is unknown.

Controversial research on ferrets conducted more than a decade ago has contributed to some of what scientists know about the potential for a pandemic of H5N1 (SN: 6/21/13). The virus may be able to travel through the air and infect ferrets, a common laboratory substitute for humans in influenza research, if certain modifications to proteins that aid in the virus’s ability to break into cells and produce more copies of itself are altered.

Jonathan Runstadler, a disease ecologist and virologist at Tufts University’s Cummings School of Veterinary Medicine in North Grafton, Mass., says that although researchers are aware that these mutations are significant in laboratory settings, it is still unclear how significant those changes are in the real world. Viruses undergo constant change, but not all genetic tweaks work together. One virus variant might benefit from the change and be able to spread more easily, while another virus variant might suffer and be less likely to do so.

Runstadler asserts, “We’re not sure how important, how big a difference, or how much to worry about those mutations when they happen in the wild.” or five years from now, when additional changes in the genetic background of the virus are influencing those initial mutations.

Researchers continue to attempt to identify specific changes despite this. Runstadler and his team look for natural viruses that have entered new animals and work backward to determine which mutations were essential. In addition, virologist Louise Moncla claims that her lab is working on ways to scan the entire genetic blueprints of viruses from previous outbreaks for signs of a virus that can cross species boundaries.

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

For instance, a change that is known to facilitate the virus’s ability to infect mice and laboratory-grown mammalian cells was found in genetic analyses of H5N1 that was prevalent on the Spanish mink farm. Changes like this could make it easier for the virus to spread to humans and other mammals. The researchers came to the conclusion that there may have been mink-to-mink transmission on the farm; however, the extent to which that particular mutation contributed to the outbreak is still unknown.

According to Runstadler, the timing of influenza viruses that are capable of spreading to mammals is a numbers game. The risk that one of the virus’s adaptations will be effective at helping the virus spread to other animals or take root and become a real problem increases the more chances you give the virus to spread and adapt.

Despite our inability to predict how humans will react to H5N1 in the future, it is evident that many bird species and some of the animals that eat them are currently dying. According to Culhane and Wille, this outbreak is also resulting in the deaths of more bird species than any other.

“We have seen immense episodes in raptors and seabirds, which were never truly impacted,” Wille says. “Unknown genetic modifications may have assisted the virus in spreading more rapidly among birds than in previous H5N1 strains. Wille says that a number of studies are trying to figure it out.

According to Moncla, these lethal avian flus have never been a persistent issue in the Americas. H5N1 variant sporadic outbreaks are typically restricted to northern Africa and parts of Asia, where the virus has infected birds since its emergence in the late 1990s.

Experts discovered more than 200 cases of a different bird flu virus in commercial and backyard poultry across the United States in 2015, marking the end of the most recent significant avian flu outbreak in North America. According to Culhane, the poultry industry slaughtered more than 45 million birds to prevent the virus from spreading. However, it remained visible to the rest of the world.

At the end of 2021, the most recent version of H5N1 arrived in North America from Europe, first appearing in Canada’s Newfoundland and Labrador province. It then moved south into the United States, where tens of millions of domestic poultry have been culled so far to stop the virus from spreading to farms where it has been found. The virus had spread to South America by December 2022. Since the middle of January, tens of thousands of pelicans and over 700 sea lions have perished in Peru.

Culhane asserts that it is essential to comprehend precisely how nonbird animals are exposed. Every organ in a bird’s body is infected by highly pathogenic avian influenzas. Thus, a fox chowing down on a contaminated bird is uncovering its own mouth, nose and stomach to a great deal of infection as it eats its feast.

In the event that H5N1 begins to spread among mammals, experts are currently keeping an eye on infected animals to raise the alarm early.

Moncla asserts, “I do think that the outbreak of mink and then the outbreak of sea lion is a wake-up call.” In order to be better prepared in the event of a change, we ought to put every piece of science we have at our disposal to try to comprehend what these viruses are doing.

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