There are more viruses than stars in the universe, and luckily, most are harmless to us. But danger can come when we're exposed to a virus we’ve never encountered before.
How Viruses Like the Novel Coronavirus Evolve
Published: June 11, 2020
Rhiju Das, PH.D.: The virus actually has probably been out there in the world and evolving, probably for a while, probably in bats, actually. And then, maybe through an intermediate animal that we don’t yet really know, it’s now jumped into humans. So, it’s not a novel entity on Earth, but it is novel in humans.
Narrator: It may be novel to us, but it belongs to a family of pathogens called “coronaviruses,” named for the spikes that protrude from their surfaces, giving them a crown-like appearance.
Coronaviruses are little more than a set of genetic instructions, wrapped in a fatty shell with protein spikes. These spikes are like keys, which lock into receptors on cells in your lungs and elsewhere. Once the virus enters, its cargo of genetic code takes over the cell’s machinery and makes new viruses, which head off to infect more cells.
At the National Institutes of Health, immunologist Kizzmekia Corbett studies these pathogens.
Kizzmekia Corbett: Coronaviruses—there are hundreds; we’ve heard about MERS and we’ve heard about SARS. There are four additional viruses that circulate in humans and cause some level of cold and sniffles and throat aches in people every single year.
Narrator: Scientists estimate there are more viruses in the world than stars in the universe. Luckily, most are harmless, whether they’re around us or in us. And many have left their mark in our D.N.A.
Das: When the human genome was sequenced at the end of the last century, I think one of the big surprises was that our genomes are full of the fragments of viruses. And they’re basically the remnants of all of these relatively harmless viral infections that we’re constantly undergoing.
Narrator: The danger can come when we run into a virus we’ve never met.
Das: When a virus jumps from another animal and finds a way to infect a human, they typically have not evolved to be a nice partner to us. They will replicate like crazy.
David Pride: And it’s very difficult on a cell, to be infected with the virus, because the virus sort of says, “Stop doing what you’re programmed to do. Instead, do what I program you to do.”
Das: Our human bodies haven’t had enough time to evolve defenses to make sure everything’s under control. And those are the viruses that we have to worry about.
Produced and Directed by: Sarah Holt
Edited by: Ralph Avellino, Ryan Shepheard, Michael H. Amundson
Digital Production: Angelica Coleman
© WGBH Educational Foundation 2020