CDC Director Dr. Tom Frieden made the announcement via Twitter on Wednesday, writing "CDC Emergency Ops Center moved to Level 1 response to Ebola outbreak given the extension to Nigeria and potential to affect many lives."
Frieden explained in a subsequent tweet that "Level 1 = highest level of activation, reserved for largest-scale responses and often require agency-wide effort."
The Ebola outbreak has been concentrated in Guinea, Liberia, and Sierra Leone but spread last month to Nigeria.
On Wednesday, the World Health Organization reported nearly 1,000 deaths from Ebola. As of August 4, a total of 932 people have died of confirmed, probable, and suspected Ebola in Guinea, Liberia, Nigeria and Sierra Leone.
"The distribution and classification of the cases are as follows: Guinea, 495 cases (351 confirmed, 133 probable, and 11 suspected), including 363 deaths; Liberia, 516 cases (143 confirmed, 252 probable, and 121 suspected), including 282 deaths; Nigeria, 9 cases (0 confirmed, 2 probable, and 7 suspected), including 1 death; and Sierra Leone, 691 cases (576 confirmed, 49 probable, and 66 suspected), including 286 deaths."
The Ebola virus is spread by close contact and typically kills up to 90 percent of its victims. There is no known cure or antivirus.