The World Health Organization has declared the Ebola outbreak in the Democratic Republic of the Congo and Uganda a Public Health Emergency of International Concern.
More than 390 suspected cases and over 100 deaths have been reported in the DRC. Two additional cases have been confirmed in Uganda.
Dr. Jean Kaseya, director general of the Africa Centres for Disease Control and Prevention, told the BBC: "We have more than 100 people already passed on, and we don't have a vaccine, we don't have medicine available to support."
The virus has been identified as the Bundibugyo strain, which carries a case fatality rate of 30% to 50%. No vaccines or treatments exist for this strain.
At least six Americans were exposed to the virus while in the DRC, though their infection status remains unclear.
The WHO says the outbreak is "extraordinary" and potentially much larger than currently reported, with high risk of cross-border spread. Ongoing conflict in DRC's Ituri Province is hampering disease surveillance and response efforts.