From a single dot in Wuhan, China, lines start to shoot out. They stretch into Thailand, Malaysia, Nepal. New colors crop up in distant lands. Soon, a multicolored web has spun across the globe.
The pulsating map found at Nextstrain.org tells the tale of a virus on the march. And that story is written in the genetic code of the virus itself.
When a virus infects a host, it churns out copies of itself. That process can be messy, and some of those copies have tiny mutations. The errors are then passed along to its “descendants” when the virus infects other people. Because those mutations occur at a regular rate, they act like a ticking molecular clock. Scientists use that clock to figure out how and when all those changes arose as viruses descended from a common ancestor in Wuhan.
Scientists around the world use powerful technologies to quickly find mutations in samples from COVID-19 patients. The Nextstrain team uses that data to build viral “family trees,” which let them trace the virus’s travels around the globe.