The Atlantic Flu viruses and coronavirus started the last few pandemics. Could the next one be a paramyxovirus? Whether it begins next week, next year, or next decade, another pandemic is on its way. Researchers can’t predict precisely when or how the outbreak might begin. Some 1.6 million viruses are estimated to lurk in the world’s mammalian and avian wildlife, up to half of which could spill into humans; an untold number are attempting exactly that, at this very moment, bumping up against the people hunting, eating, and encroaching on those creatures. (And that’s just viruses: Parasites, fungi, and bacteria represent major infectious dangers too.) The only true certainty in the pandemic forecast is that the next threat will be here sooner than anyone would like.
But scientists can at least make an educated guess about what might catalyze the next Big One. Three main families of viruses, more than most others, keep scientists up at night: flu viruses, coronaviruses, and paramyxoviruses, in descending order of threat. Together, those groups make up “the trifecta of respiratory death,” Sara Cherry, a virologist at the University of Pennsylvania, told me.
Flu and coronavirus have a recent track record of trouble: Since 1918, flu viruses have sparked four pandemics, all the while continuing to pester us on a seasonal basis; some scientists worry that another major human outbreak may be brewing now, as multiple H5 flu viruses continue to spread from birds to mammals. The past two decades have also featured three major and deadly coronavirus outbreaks: the original SARS epidemic that began in late 2002; MERS, which spilled into humans—likely from camels—in 2012; and SARS-CoV-2, the pandemic pathogen that’s been plaguing us since the end of 2019. Common-cold-causing coronaviruses, too, remain a fixture of daily living—likely relics of ancient animal-to-human spillovers that we kept transmitting amongst ourselves.
Paramyxoviruses, meanwhile, have mostly been “simmering in the background,” says Raina Plowright, a disease ecologist at Cornell. Unlike flu viruses and coronaviruses, which have already clearly “proven themselves” as tier-one outbreak risks, paramyxoviruses haven’t yet been caught causing a bona fide pandemic. But they seem poised to do so, and they likely have managed the feat in the past. Like flu viruses and coronaviruses, paramyxoviruses can spread through the air, sometimes very rapidly. That’s certainly been the case with measles, a paramyxovirus that is “literally the most transmissible human virus on the planet,” says Paul Duprex, a virologist at the University of Pittsburgh. And, like flu viruses and coronaviruses, paramyxoviruses are found in a wide range of animals; more are being discovered wherever researchers look. Consider canine distemper virus, which has been found in, yes, canines, but also in raccoons, skunks, ferrets, otters, badgers, tigers, and seals. Paramyxoviruses, like flu viruses and coronaviruses, have also repeatedly shown their potential to hopscotch from those wild creatures into us. Since 1994, Hendra virus has caused multiple highly lethal outbreaks in horses, killing four humans along the way; the closely related Nipah virus has, since 1998, spread repeatedly among both pigs and people, carrying fatality rates that can soar upwards of 50 percent.