.dropcap { color: #838078; float: left; font-size: 82px; line-height: 60px; padding: 5px 8px 0 0; } When Tony Goldberg received an exuberant, enigmatic text message—“You gotta come into the lab!”—the epidemiologist turned his car around and headed straight back to his office at the University of Wisconsin, Madison. He found his postdoc, Sam Sibley, transfixed by the computer monitor. Sibley had just finished running blood serum from a long-dead Bald Eagle through a powerful machine that searches out all traces of genetic material. Comparing the results to a database of all the world’s known viruses, the computer had spit back a surprising match. Peering at the screen, Goldberg realized the viral code displayed before him was something completely new. Bizarrely, it appeared to be a relative of human hepatitis C, an infectious disease that causes liver damage. At the time, in 2017, a virus of this type had never been found in a bird before. It...