The outbreak of Ebola virus disease in West Africa is the most severe ever recorded. The outbreak originated in Guinea (the first case was reported on March 21, 2014, but cases were traced to December 2013) and spread to Sierra Leone and Liberia, the three countries with the highest transmission.

Nigeria and Senegal also reported imported cases and local transmission, but these were controlled by mid-October 2014. Spain, the United States, and Mali also reported one or more cases of people infected in West Africa or while attending patients infected in these countries.

WHO plays a key leadership role in response efforts in public health. The main priority is to contain and stop the outbreak in West Africa, preventing further spread and helping affected communities. A special UN mission was created to combat the disease.