The Worst Disease Ever Recorded

A century ago, a strain of pandemic flu killed up to 100 million people—5 percent of the world’s population. In 2013, a new mystery illness swept the western coast of North America, causing starfish to disintegrate. In 2015, a big-nosed Asian antelope known as the saiga lost two-thirds of its population—some 200,000 individuals—to what now looks to be a bacterial infection. But none of these devastating infections comes close to the destructive power of Bd—a singularly apocalyptic fungus that’s unrivaled in its ability not only to kill animals, but to delete entire species from existence.

Bd—in full—kills frogs and other amphibians by eating away at their skin and triggering, but that figure is almost two decades out-of-date. New figures, compiled by a team led by from the Australian National University, .