Ebola is a violent killer. The symptoms, at first, mimic the flu: headache, fever, fatigue. What comes next sounds like something out of a horror movie: significant diarrhea and vomiting while the virus shuts off the blood's ability to clot.
As a result, patients often suffer internal and external hemorrhaging. Many die in an average of 10 days.
People are traveling without realizing they're carrying the deadly virus. It can take between two and 21 days after exposure for someone to feel sick.
The good news is that Ebola isn't as easily spread as one might think. A patient isn't contagious -- meaning they can't spread the virus to other people -- until he or she is showing symptoms.
The disease is transmitted by direct contact with the blood and body fluids of infected animals or people, according to WHO.
The scientist who discovered the Ebola virus in the 1970s, Dr. Peter Piot, told CNN's Christiane Amanpour this week that the situation is "unprecedented."
"One, (this is) the first time in West Africa that we have such an outbreak," he said. "Secondly, it is the first time that three countries are involved. And thirdly, it's the first time that we have outbreaks in capitals, in capital cities."
Officials believe the wide footprint of this outbreak is partly because of the proximity between the jungle where the virus was first identified and cities such as Conakry, Guinea's capital, which has a population of 2 million and an international airport.
Complicating matters, the countries hit hardest by the epidemic have major medical infrastructure challenges.
There is no cure for Ebola, but in theory, the disease should be easy to fight since close contact is needed to become infected, Piot said.
Simple hygienic measures such as washing with soap and water, not reusing syringes and avoiding contact with infected corpses are sufficient to stop spread of the disease, Piot said.
"This is an epidemic of dysfunctional health systems," he added. "Fear of the virus, and the lack of trust in government, in the health system, is as bad as the actual virus."