The Yambuku Mission Hospital sat in the Bumba Zone of Zaire's Equator Region, a landscape of tropical rainforest where roughly 275,000 people lived in scattered villages, most with fewer than 5,000 inhabitants. Many of these communities bordered the Congo River, connected to each other by water and footpath rather than by road. The hospital served as the area's primary medical facility. Belgian nuns ran much of it, and the prenatal clinic gave routine vitamin injections to pregnant women -- a well-intentioned practice that became the vehicle for an epidemic. Peter Piot, the Belgian microbiologist who helped investigate the outbreak, later concluded that the unsterilized needles had carried the virus from an initial, still-unidentified infected person through patient after patient. The correlation between injection history and Ebola cases was unmistakable.

When blood samples from Yambuku reached laboratories in Belgium and the United States, researchers initially suspected Marburg virus, a hemorrhagic fever pathogen identified nine years earlier in Germany. Under the electron microscope, the new pathogen looked similar but not identical. It was longer, more sinuous, shaped like a shepherd's crook. The scientists realized they were dealing with something previously unknown. They named it after the Ebola River, which flowed near Yambuku -- a geographic convention that gave a local landmark a permanent and grim association. The 318 cases and 280 deaths in Zaire, combined with 284 cases and 151 deaths from a separate, unrelated outbreak in what is now South Sudan, constituted the first recorded emergence of Ebola virus disease anywhere in the world.

Yambuku Mission Hospital closed after 11 of its 17 staff members died. Among the dead were two Belgian nuns who had served the community for years. Mayinga N'Seka, a young Zairean nurse, also succumbed after traveling to Kinshasa seeking treatment -- a journey that briefly raised the terrifying possibility of the virus reaching the capital. Because the cause of the illness was initially unknown, many patients were misdiagnosed with malaria, yellow fever, or typhoid and given treatments that did nothing. The hospital itself, the only significant medical facility in the region, had become the primary engine of transmission. It was a cruel irony that the institution dedicated to healing had amplified the very disease it was trying to treat.

With assistance from the World Health Organization, the outbreak team adopted the bluntest available strategy: quarantine entire villages, sterilize all medical equipment, and provide protective clothing to anyone who came near the sick. The small Zairian Air Force contributed helicopters that allowed investigators to visit 550 villages across the affected region. Cases were documented in 55 of them. The majority of infections had occurred in the first four weeks of September, and the last probable case died on November 5, 1976. The outbreak burned itself out largely because the forest's geography did what medicine could not -- the isolation of small villages along distant rivers limited the virus's ability to spread beyond each cluster. Yambuku's tragedy gave the world its first warning about Ebola. The Democratic Republic of the Congo has since experienced at least eleven more outbreaks, but none erased the memory of where it began.