ARI SHAPIRO, HOST:
Many viruses have the potential to cause pandemics, but it is the rare virus that actually succeeds. NPR's Pien Huang looks into the superpower combination of traits that have helped the coronavirus go global.
PIEN HUANG, BYLINE: Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, says the coronavirus is a once-in-a-century virus.
TEDROS ADHANOM GHEBREYESUS: It has very peculiar features. And the world has never seen anything like this for several decades.
HUANG: All the way back to the 1918 flu pandemic. Carlos Zambrana-Torrelio agrees. He's an ecologist with the nonprofit EcoHealth Alliance, and he says there are hundreds of coronaviruses in bats alone that could theoretically infect people. He also estimates that there are 1.7 million viruses living in other mammals and birds.
CARLOS ZAMBRANA-TORRELIO: A fraction of those are pathogenic, and just a few of those will become pandemic.
HUANG: Most of these viruses don't have the right combination to be completely explosive. Dr. Megan Freeman, a virologist at Children's Hospital of Pittsburgh, says the coronavirus combines a few key traits that make it really difficult to control. Some of these characteristics are well known by now.
MEGAN FREEMAN: So I think transmissibility from human to human is one of its biggest superpowers.
HUANG: Freeman says it's highly contagious, and you don't have to touch someone to get it. All it takes is getting close enough to someone who is infected and breathing in their respiratory droplets. One infected person can get on a plane and spread the virus to a new continent. Another trait, says Andrea Pruijssers, a virologist at Vanderbilt University, is when it's contagious.
ANDREA PRUIJSSERS: For SARS-CoV-2, a lot of the transmission is from asymptomatic or mildly symptomatic people.
HUANG: That makes it really hard to stop people from passing the virus on. You basically have to assume that anyone you come in contact with could be infected at any given time without knowing it. That's why mask-wearing is required in many public spaces. Pruijssers says another trait we're starting to learn about is the virus's ability to jump from people to different kinds of animals.
PRUIJSSERS: We know that it can affect cats and ferrets and minks and all of these animals that are living in close proximity to humans.
HUANG: Pruijssers says this suggests that if the virus starts circulating regularly among animals that we handle or live with it, it might be really hard to ever get rid of. A community could be virus-free only to have it reintroduced by a visiting cat. So the coronavirus is highly contagious, it spreads without symptoms, and it jumps with ease between humans and animals. Lots of viruses have some of these traits, but altogether they've created a perfect-storm virus that's causing a once-in-a-century pandemic.
PRUIJSSERS: And, of course, we know nothing about it. It's a brand-new virus.
HUANG: Pruijssers says it means that everyone is susceptible to it. And researchers have had to figure out everything from scratch - how it spreads, who's more likely to get sick from it and how to combat it with drugs and vaccines. She says there's a lot we still don't know, but we are learning fast. Pien Huang, NPR News.
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