Dr. Peter Piot was just 27, a budding virologist with a thirst for adventure, when he was dispatched to the heart of Africa to track down a terrifying virus that he had helped discover.

It was 1976, and the virus had arrived at his laboratory in Antwerp, Belgium, in a blue plastic cooler holding two glass tubes of blood. They had been sent from Zaire (now the Democratic Republic of Congo) by a doctor caring for a Flemish nun who was dying of fever and loss of blood.

One tube was intact. The other was broken; its contents mingled with melted ice to form a red soup. A bloodstained note said the nun was among 200 people, including doctors and nurses, dying in an outbreak that had raged for three weeks in remote Yambuku, not far from the Ebola River.

The prime suspect was yellow fever, a mosquito-borne infection that Dr. Piot’s laboratory at the Institute of Tropical Medicine was equipped to detect. But unknown to anyone then, the nun’s blood harbored the virus that was soon to be named Ebola.