This article was changed on June 25 to add updated information.

An outbreak of the terrifying Ebola virus emerged in the West African nation of Guinea in February and has been spreading ever since, infecting people in Sierra Leonne and Liberia as well. It is now the biggest and deadliest outbreak of Ebola since the virus was identified in 1976.

Recent investigations by public health authorities suggest that it actually may have first emerged undetected as early as December.

The disease's spread seemed to slow down for a while, but has picked up in recent weeks. An estimated 599 people have been infected, and 338 have died in Guinea, Sierra Leone and Liberia. While it's likely that many cases go uncounted, the Associated Press notes that previously, the largest reported death toll was in the Congo in 1976, when 280 people died. (The most widespread outbreak infected 425 people in Uganda in 2000, killing 224.)

"The epidemic is now in a second wave," Bart Janssens, the director of operations for Doctors Without Borders told the Associated Press. "It is totally out of control."

The 32 new cases reported June 24 were all in Liberia and Sierra Leone; two new deaths (but no new cases) were reported in Guinea. The three countries affected by this latest outbreak met on June 23 to "enhance coordination, information management, and communication," according to the World Health Organization.

"There needs to be a real political commitment that this is a very big emergency," Janssens added. "Otherwise, it will continue to spread, and for sure it will spread to more countries."

This outbreak is unique because it has struck densely populated areas like Monrovia, the capital of Liberia, and Conakry, the capital city of Guinea, where there have been 65 cases and 33 deaths. Ebola usually emerges in sparsely populated rural regions, where fewer people pass through.

"Major challenges faced by all partners in the efforts to control the outbreak include its wide geographic spread, weak health-care infrastructures, and community mistrust and resistance," the CDC noted in a recent update.

In an interview with NBC News, Robert Garry, a microbiology professor at the Tulane University School of Medicine, warned that the outbreak so far is just "the tip of the iceberg."

Still, in its latest update, the World Health Organization said it "does not recommend any travel or trade restrictions be applied to Guinea, Liberia, or Sierra Leone based on the current information available."

Ebola is one of the deadliest viruses ever known, with the most fatal strains killing up to 90% of people infected. The current strain has killed 66% of those infected in Guinea, 51% of those infected in Sierra Leone, and 73% of those infected in Liberia.

Ebola begins as fever, weakness, muscle pain, headache, and sore throat, but soon progresses to vomiting, diarrhea, rash, and impaired organ function. A large proportion of those infected also bleed profusely, both internally and externally. It's considered highly contagious, though it isn't transmitted through the air — instead it's spread by bodily fluids like blood and saliva, which can be very hard to avoid when someone is bleeding heavily from every orifice.

Ebola first emerged in humans in 1976, and there have been more than 18 outbreaks since then. There is currently no vaccine and no cure.