CAMBRIDGE, Mass. — The fluorescent orange sticker atop the white machine reads “BIOHAZARD,” but it’s a bit of a misnomer. Although Earth abounds with pathogens that can maim, kill, paralyze, and poison, the specimens inside this machine — being pipetted left and right behind glass for sequencing — are probably the most innocuous human viruses you will ever encounter.
In fact, you have already encountered them: Right now, millions of these bugs, called anelloviruses, are swimming backstroke through your blood and lounging in the hot springs of your cells, harmless as a house cat. They have been found in astonishing variety on every inhabited continent and nearly every age group but somehow never seem to cause disease.