A WHO-organized meeting on the current, West African Ebola outbreak is occurring today and tomorrow in Ghana. The outbreak began several months ago in Guinea, with a significant mortality event in mid-March, and now a significantly larger and more extensive second outbreak has occurred in May/June. According to CDC numbers, it has now officially become the worst outbreak, in terms of fatalities, in the ~50 year (known) history of the disease, with 441 dead. Ebola emerged without warning in Zaire in 1976, and the viral family it belongs to, the Filoviridae, was not even discovered until 1967 (see this interesting document). The WHO estimates the mortality at 291 confirmed and 467 probable. The cause of the difference in the two mortality estimates is not immediately clear to me. You can learn more about Ebola and Marburg, two of the hemorrhagic viruses, here. Here is a summary of how the WHO is handling the situation.
The growth in Zaire Ebolavirus cases as of June 24, n = 607. LAB+: laboratory confirmed. Source.