When the cattle began dying in British Cape Colony in southern Africa, no one knew why. It was 1896 and germ theory — the idea that disease is caused by nearly invisible living organisms — was still relatively new.

Four years before these events, Jotello Soga, a well-regarded veterinarian, had warned that a coming epidemic threatened to destroy the region’s livestock.

“I make bold enough to say, that more than two-thirds of Colonial cattle will succumb to its ravages,” Soga wrote in an 1892 scientific journal article.