The World Health Organisation has summoned experts to an emergency meeting to advise on the international response to the outbreak which has now hit Mbandaka.
They will decide whether it constitutes a “public health emergency of international concern”.
Officials are already rushing experimental vaccines to the crowded city of Kinshasa to avoid a nightmare scenario – which would see the disease spread like wildfire as millions live in unsanitary slums not connected to a sewer system.
Ebola has spread to the city of Mbandaka
Congolese Health Ministry officials carry the first batch of experimental Ebola vaccines in Kinshasa
WHO bosses said the DRC risk had been escalated from “high” after the first confirmed case in Mbandaka, a city of around 1.5 million.
The risk to neighbouring countries has been lifted to “high” from “moderate”.
A WHO spokesman said: “The confirmed case in Mbandaka, a large urban centre located on major national and international river, road and domestic air routes increases the risk of spread within the Democratic Republic of the Congo and to neighbouring countries.”
WHO deputy director-general for emergency preparedness and response, Peter Salama said: “We’re certainly not trying to cause any panic in the national or international community.
“What we’re saying though is that urban Ebola is very different phenomenon to rural Ebola because we know that people in urban areas can have far more contacts so that means that urban Ebola can result in an exponential increase in cases in a way that rural Ebola struggles to do.”
WHO said there had been 21 suspected, 20 probable and three confirmed cases of Ebola between April 4 and May 15, a total of 44 cases, including 15 deaths.
Mbandaka had three suspected cases in addition to the confirmed case.
A health worker is sprayed with chlorine after visiting an Ebola ward
WHO is rushing out 7,540 doses of an experimental vaccine to try to stop the outbreak in its tracks, and 4,300 doses have already arrived in Kinshasa.
It will be used to protect health workers and “rings” of contacts around each case.
The vaccine supplies will be enough to vaccinate 50 rings of 150 people.