Via Vanity Fair, a major report with remarkable details about the start of the outbreak: Why a Massive International Effort Has Failed to Contain the Ebola Epidemic. Excerpt:
As near as anyone can tell, the outbreak started when a few tiny rod-shaped particles—each merely an attack plan coded in ribonucleic acid and wrapped in a protein shell—found their way from a fruit bat into the body of a child not yet two years old.
Perhaps, while the mother was preparing the day’s hunt, some of the bat’s blood was flung in the child’s direction. Perhaps, while the mother’s attention was elsewhere, the child touched the animal, then brought his hand to his mouth, the way babies do.
Either way, a few strands of the Ebola virus attached themselves to cells in the child’s immune system and used the cells’ machinery to replicate. The boy developed a fever, then diarrhea and vomiting. His organs began to fail. He began to bleed internally and went into septic shock. In four days, he was dead.
It might have ended there—one child’s death in the jungle, way back in December—with no one ever to know that Ebola had spilled over into the human population. Certainly this happens often—spillovers that produce outbreaks so sudden, and generally so remote, that they don’t spread. People close by attribute the deaths to some other, more common affliction, while people far away never hear about them at all.
In this case, however, a family dispute intervened. After the child was infected but before he died, the mother, who happened to be pregnant, packed up the boy and a daughter and marched across the village to her own mother’s house. Space there was tight, because the grandmother had a houseguest. Beds were shared, and the baby’s symptoms exploded. His mother was infected, his sister, his grandmother, the houseguest too. When the mother miscarried, the midwife was infected. The Ebola virus had started to move.
When Ebola strikes, it kills quickly, but it can take up to three weeks to incubate, and usually around 10 days. The period is long enough that contact with a possible source may have been forgotten, and long enough for infected people to travel without symptoms.
And even if you tested for Ebola—which nobody in Guinea had the capacity to do—you wouldn’t find it during the incubation period: Ebola can’t be detected in the blood until symptoms show. An epidemic can start slowly and go unnoticed for weeks. This has never been much of an issue before, because Ebola tends not to find its way into large population centers, or places where people are very mobile.
This time would be different.