The deadliest Ebola outbreak in history

The Ebola virus has now hit four countries: Sierra Leone, Guinea, Liberia, and recently Nigeria, according to the country's ministry of health. The virus — which starts off with flu-like symptoms and often ends with horrific hemorrhaging — has infected 1,201 people and killed an estimated 672 since this winter, according to the numbers on July 23 from the World Health Organization. Ebola is both rare and very deadly. Since the first outbreak in 1976, Ebola viruses have infected thousands of people and killed roughly 60 percent of them. Symptoms can come on very quickly and kill fast. Journalist David Quammen put it well in a recent New York Times op-ed: "Ebola is more inimical to humans than perhaps any known virus on Earth, except rabies and HIV-1. And it does its damage much faster than either." So why is Ebola doing so much damage right now?
Here's a primer on what's going on.