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Scientific American
5 days ago
- Health
- Scientific American
Gene-Swaps Could Let Influenza Jump Species
Influenza viruses are shifty entities. They accumulate small genetic changes on a regular basis, necessitating yearly updates to the flu vaccines because the prior year's strain may not look much like the following year's. But they can also make sudden leaps by incurring big genetic changes that may allow them to jump from one animal species to another or to humans. A seemingly ingenious and sneaky way for viruses to make these leaps is by swapping genetic material with other flu strains. Called reassortment, this exchange happens when a person or animal is infected with two types of flu virus at the same time. While replicating inside the host cell, the viruses can grab bits of each other's genetic code and incorporate them into their own gene sequences. Reassortment is much less common than small mutations that change the flu year to year, but it's important: at least three of the last four human flu pandemics have involved reassortment. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. 'Reassortment has played a major, major role in the emergence of pandemic influenza,' says Daniel Perez, a professor of poultry medicine at the University of Georgia College of Veterinary Medicine, who studies how flu moves between species. The past century saw four flu pandemics. The first was the notorious 1918 Great Influenza, which killed around 50 million people. The second was in 1957, when a new flu killed between one million and four million people worldwide. In 1968 another new flu emerged, killing another one million to four million people. Finally, in 2009, a novel swine flu appeared, killing between 151,000 and 575,000 people that year. Flu viruses are categorized by two types of proteins on their surfaces, hemagglutinin (HA) and neuraminidase (NA). These proteins each have multiple subtypes, which is why you'll see labels such as H1N1 or H5N1. The H refers to the HA protein type, and the N refers to the type of NA protein. The Great Influenza that swept the globe during World War I was an H1N1 flu that likely emerged in Kansas. Its descendants circulated in both humans and pigs until 1957, when it was suddenly replaced in humans by an H2N2 flu. This new virus first popped up in southern China. Its main genetic backbone belonged to the 1918 flu, Perez says, but it had acquired three new gene sequences from an avian flu, swapping its HA and NA proteins for new subtypes. For reasons not completely understood, this new H2N2 wiped out H1N1 in humans for decades—H1N1 wouldn't be seen again in people until 1977. The 1968 pandemic was another reassortment event. This time, the H2N2 that was circulating in humans swapped genes with an H3N2 avian influenza, probably somewhere in China. (The first identified outbreak was in Hong Kong.) Then came the 2009 pandemic, a true 'globalized pandemic,' Perez says. In the early 2000s there had been a few sporadic human infections in the U.S. with so-called triple-reassorted flu viruses that contained genes from human, avian and swine influenzas. These cases were rare and mostly in people who worked on pig farms; these viruses didn't transmit from human to human. That changed in 2009 when the triple-reassorted viruses picked up new genes from a Eurasian swine flu. 'It's a perfect example of globalization,' Perez says, 'because the virus contains not only gene segments from an avian flu, from a swine flu [and] from a human flu but also from very different geographical locations.' The reassortment of flu viruses that infect different species fortunately happens relatively infrequently, says Charlotte Kristensen, a postdoctoral researcher in veterinary clinical microbiology at the University of Copenhagen. 'It has to be two different viruses infecting the same host cell, and the reassortment has to be successful. And it's not always like the gene segments are compatible,' she says. Such reassortment happens all the time between avian flu strains that infect birds, says Yuan Liang, also a University of Copenhagen veterinary clinical microbiology postdoctoral researcher. 'Especially since 2020, there have been a lot of new variants emerging because of reassortments' in birds, Liang says. The various strains of H5N1 circulating now in wild birds, domestic poultry and dairy cows have yet to cause a pandemic in people. It's hard to say whether the virus will stay mostly in animals or whether we're now in a period like the one before the 2009 flu pandemic, when farmworkers occasionally came down with a reassorted virus that would later gain the gene sequences it needed to spread from person to person. No one expect H5N1 to take hold in dairy cattle, Liang says, so the question now is what new, unexpected step this virus might take. 'This whole situation really highlights how little we know and how complex it is,' Kristensen says.
New York Times
15-03-2025
- Health
- New York Times
Five Years On, Ghosts of a Pandemic We Didn't Imagine Still Haunt Us
Five years later, the everyday has returned to the pleasant New Jersey town of Maplewood. About the only visible trace of what was endured is the urgent plea that still adorns the caution-yellow marquee of the old movie theater. There for the last five years, ever since the theater closed at the dawn of the dread, it says: STAY HEALTHY. The letter L is tipped slightly, like someone staggered by a blow. That letter L might as well be us, upright but still staggering from a pandemic that killed more than seven million people worldwide, including 1.2 million in the Maplewoods and metropolises of America. Time's passage has granted the illusion of distance. The veils of protection have dropped from faces, and crowds are once again bellying up to the bar, their conversations carrying echoes of what was being talked about at the start of 2020, as if the last five years had been excised from the calendar. But then something noticed, something heard, unearths something buried. A message on a closed movie theater's marquee. A face mask shoved in a drawer. A silhouette of footprints on a subway platform. The strains of a familiar John Prine song, maybe 'Angel From Montgomery,' which at first makes you smile because you love all things Prine, but then you remember that he died in 2020 of complications from Covid, and before the next chord plays your mind is back in that dystopian time. The collective impulse to compartmentalize and forget has kicked in before. The flu pandemic of 1918 to 1920 infected nearly a fifth of the American population, yet an early chronicling of the 1920s that is now considered a classic of its kind — 'Only Yesterday,' written by the journalist Frederick Lewis Allen and published in 1931 — made only passing mention of the Great Influenza: just three dozen words for a national disaster that killed anywhere from a half-million to 850,000 people. A century later, that impulse to suppress has returned, muddling our sense of time. The coronavirus pandemic can seem so safely submerged in the past that we sometimes have to stop and ask ourselves: Did that really happen? It did. Five years ago this month, the World Health Organization declared a pandemic, the federal government declared a national emergency — and the United States all but lurched to a halt. Schools, offices, stores and places of worship closed, and sheltering in place, a concept antithetical to community, became an unnatural way of life. There was at first something sci-fi unreal about the coronavirus — an invisible enemy whose means of contagion remained mysterious. But then came the reality of death, by the thousands, the tens of thousands: so many that hospitals and funeral homes could not keep up; so many that bodies were stacked almost like cordwood in refrigerated trucks. The pandemic disrupted the ancient and sacred rituals of mourning, denying many the primal need to say goodbye. Unable to gather, we could not recite prayers together, or share comforting hugs or even toss a parting rose upon on a casket. We watched the burials of our loved ones from a distance, often in the cocoon of cars. Remember? As scientists raced to develop a vaccine, we lived in the uncertain, even the absurd, as government officials under pressure struggled to land upon the best course of action. Amid this life-and-death confusion, we slathered our hands with sanitizer whenever we touched a doorknob. We stood in line to walk like zombies through the disquieting stillness of supermarkets. We cotton-swabbed our noses while sitting in our cars, shoved the packed-up sample through a pharmacy's drive-up window — and waited to see if the touch of that doorknob, or the walk through that supermarket, had risked our lives. Nearly a year into the madness, a vaccine became widely available, and most of us, though not all, grasped how vaccinations would stem the contagion and save lives. New terms joined the Covid vernacular. In addition to waves and surges and hot spots, we had the three witches of variants: Alpha, Delta and Omicron. We asked one another a single question — Are you Pfizer or Moderna? — as we fretted whether we'd chosen the most efficacious vaccine. Finally, in April 2023, President Joseph R. Biden Jr. signed into law a resolution to end the coronavirus national emergency declared three years earlier. The pandemic storm, it seemed, was behind us now. Nonsense. We continue to live in its wake. The repercussions of Covid extend beyond the hundreds of people it still kills a week, beyond the many who still suffer from long Covid, beyond the ghostly restaurants and storefronts that could not withstand the sudden and sustained plummet in business. A cohort of adolescents and young adults missed out on the learning that occurs in and out of the classroom: the labs and proms and presentations and graduations. At the same time, many of their parents continue to work from the isolation of their homes, a virtual-first experience that frees up time at the expense of any creativity sparks from face-to-face contact. The pandemic turned us against one another. Were we pro-mask or anti-mask? Pro- or anti-vaccination? Did we believe in the sanctity of individual rights or in suspending certain freedoms for the communal good? The anger spurred by masks and other Covid-related rules and requirements helped to further fuel a distrust of government: a distrust embraced by those now in government. Vaccinations for the coronavirus recently saved millions of lives in this country, and yet the new head of the Department of Health and Human Services — the federal agency created to protect the health of the American public — has long been hostile to this tried-and-true method of immunization. At times it seems the collective impulse to suppress has worked too well. As though we never heard the hum of those refrigerated trucks. As though we have forgotten just how vulnerable we were, and are.
