Officials said more than 513 cases were suspected in DR Congo as of Tuesday, while one person has died in neighbouring Uganda. BBC reported.
The WHO's Dr Anne Ancia told the BBC that the more the agency investigates the outbreak, the clearer it becomes cases have spread to other areas.
Modelling by the London-based MRC Centre for Global Infectious Disease Analysis released on Monday suggested there had been "substantial" under-detection, and that it could not rule out there had already been more than 1,000 cases.
The study suggested that the current outbreak is "larger than currently ascertained" and that its "true magnitude remains uncertain".
A man who spoke to BBC News and identified himself as Bigboy said people are "really scared" and doing what they can to protect themselves.
He said locals are taking precautions such as washing hands with clean water, but added that he wished they could get access to other protective supplies such as face masks.
Another Ituri local, Alfred Giza, said people in the community are aware of the threat and waiting to receive face masks to protect themselves, but that he would not know what to do if a family member or friend contracted the disease.
