Patient Zero in the Ebola outbreak, researchers suspect, was a 2-year-old boy who died Dec. 6, just a few days after falling ill in a village in Guéckédou, in southeastern Guinea. Bordering Sierra Leone and Liberia, Guéckédou is at the intersection of three nations, where the disease found an easy entry point to the region.

A week later, it killed the boy's mother, then his 3-year-old sister, then his grandmother. All had fever and vomiting, but no one knew what had sickened them.

Two mourners at the grandmother's funeral took the virus home to their village. A health worker carried it to still another, where he died, as did his doctor. They both infected relatives from other towns. By the time Ebola was recognized, in March, dozens of people had died in eight Guinean communities, and suspected cases were popping up in Liberia and Sierra Leone — three of the world's poorest countries.

In Guéckédou, where it all began, "the feeling was fright," said Dr. Kalissa N'fansoumane, the hospital director. He had to beg his employees to come to work.

On March 31, Doctors Without Borders, which has intervened in many Ebola outbreaks, called this one "unprecedented," and warned that the disease had erupted in so many locations that fighting it would be enormously difficult.

Now, with 1,779 cases, including 961 deaths and a small cluster in Nigeria, the outbreak is out of control and still getting worse. Not only is it the largest ever, but it seems likely to surpass all two dozen previous known Ebola outbreaks combined. Epidemiologists predict it will take months to control, and a spokesman for the World Health Organization said thousands more health workers were needed to fight it.

Some experts warn that the outbreak could destabilize governments in the region. It is already causing widespread panic and disruption. On Saturday, Guinea announced that it had closed its borders with Sierra Leone and Liberia in a bid to halt the virus' spread. Doctors worry that deaths could shoot up from malaria, dysentery and other diseases as Ebola drains resources from weak health systems. Health care workers, already in short supply, have been hit hard: 145 have been infected, and 80 of them have died.

Past Ebola outbreaks have been snuffed out, often within a few months. How, then, did this one spin so far out of control? It is partly a consequence of modernization in Africa, and perhaps a warning that future outbreaks — which are inevitable — will pose tougher challenges. Unlike most previous outbreaks, which occurred in remote spots, this one began in a border region where roads have been improved and people travel a lot. The disease was on the move before health officials even knew it had struck.

New York Times