AP Photo/Kjell Gunnar Beraas, MSF Healthcare workers from the Doctors Without Borders prepare isolation and treatment areas for their Ebola, hemorrhagic fever operations, in Gueckedou, Guinea.

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. The World Health Organisation announced new numbers on Tuesday, in what is now the biggest and deadliest outbreak of Ebola since the virus was identified in 1976.

The disease’s spread seemed to slow down for a while, but has picked up in recent weeks. An estimated 759 people have been infected, and 467 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.)

Here are the latest numbers, from the World Health Organisation:

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

“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.”

“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 areas like Monrovia, the capital of Liberia, and Conakry, the capital city of Guinea. Ebola usually emerges in sparsely populated rural regions, where fewer people pass through.

The WHO identified three major factors that are contributing to the continuing spread of Ebola:

“Strong cultural practices and traditional beliefs” in rural areas mean that traditional funeral practices, fear, and misinformation make the outbreak difficult to contain.

The disease, historically a product of primarily rural areas, is now in densely populated cities.

Ebola has spread across the porous borders of Guinea, Liberia, and Sierra Leone, where, the WHO notes, “commercial and social activities continue.”

“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 Organisation 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 closer to 60% of those infected, based on the numbers we have so far, which are likely to change over time.

Ebola begins as fever, weakness, muscle pain, headache, and sore throat, but soon progresses to vomiting, diarrhoea, 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.

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