The Premonition: A Pandemic Story

by Michael Lewis

There’s a widely agreed-upon standard of proof in virology, collectively called Koch’s postulates, for the German doctor who first developed the criteria, in the late nineteenth century. “The only way to prove that a virus causes a disease is to isolate the virus and inject it into a healthy animal,” Joe explained. “If the injection causes the disease, everyone agrees that you’ve proved your case.” To prove that the virus they’d isolated was killing boas and pythons, they’d first need to grow this ancient ancestor of Ebola in the lab, find some healthy boas and pythons, and then infect them with the virus. To inject a virus into an African python took some trouble. Snakes don’t have injectable veins. They do, perhaps surprisingly, have hearts, and that’s where the virus must be injected. Snake hearts don’t stay put, like human hearts, but travel up and down the snake’s body. To inject a snake’s heart with a virus requires two postdocs and one full professor: one to hold the snake in a death grip, one to use a Doppler radar to find the snake’s heart, and a third to plunge the needle into it.

Proving Causation: Science, Snakes, and the Challenge of Koch’s Postulates