Washington (AFP) - A top US health official urged swift action Thursday to prevent the deadly Ebola virus from becoming the next AIDS epidemic, as the health of an infected Spanish nurse deteriorated.

The United Nations chief meanwhile called for a 20-fold increase in the world's response to the spread of Ebola, which has killed nearly 3,900 people in West Africa since the beginning of the year.

Ebola's spillover into the United States and Europe has raised fears of a wider outbreak, and led the United States, Canada and Britain to start tougher airport screening of passengers arriving from West Africa.

The US Centers for Disease Control and Prevention predicted the number of cases could mount to 1.4 million by January unless strong measures are taken to contain the disease, which is spread though close contact with the bodily fluids of an infected person.

"We have to work now so that it is not the world's next AIDS," CDC Director Tom Frieden told the heads of the United Nations, World Bank and International Monetary Fund gathered in Washington.

"I would say that in the 30 years I've been working in public health, the only thing like this has been AIDS," he added, warning of a "long fight" ahead.

- Spanish nurse -

In Madrid, the condition of a nurse who treated two elderly missionaries with Ebola worsened, leaving her at "serious risk" of dying, Madrid regional president Ignacio Gonzalez told parliament.

Teresa Romero is the first person infected with Ebola outside Africa.

Health officials said they would monitor about 50 other people -- mostly health staff -- who had been in contact with Romero for the duration of the 21-day Ebola incubation period.

Six other people are in quarantine at the hospital as a precaution, including Romero's husband and several health workers, according to the latest tally from the hospital.

Among Ebola's latest victims is Thomas Eric Duncan, the first patient cared for in the United States to die of the disease.

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Just after his death was announced Wednesday, US officials ordered increased screening at five major airports in Atlanta, Chicago, New Jersey, New York and Washington.

French Health Minister Marisol Touraine said she was working with the authorities in countries badly affected by Ebola "to see in which conditions we can reinforce departure controls."

Britain said it would start "enhanced screening" of people coming from Ebola-hit parts of West Africa at Heathrow and Gatwick airports and on Eurostar trains from Belgium and France.

The European Commission was expected to meet on October 17 to discuss possible new ways to monitor passengers arriving from affected countries.

- 'Just take action' -

The continuing outbreak in West Africa forced officials in Liberia -- the nation worst hit by the Ebola outbreak -- to postpone nationwide elections.

Almost three million voters had been due to go to polling stations on Tuesday but organizers said there was no way a "mass movement, deployment and gathering of people" could go ahead without endangering lives.

In Guinea, global aid agency Medecins Sans Frontieres said a surge of Ebola cases had pushed its treatment unit in the capital Conakry to its "physical limits."

Speaking to the UN, World Bank and IMF chiefs in Washington, Sierra Leone President Ernest Bai Koroma assailed the global response to the epidemic thus far, saying it was moving more slowly than the spread of the disease.

"This slower-than-the-virus response needs to change," he said.

UN Secretary-General Ban Ki-moon said resources to support the fight must be increased 20-fold, and urged nations to act without delay.

"Cases are growing exponentially," Ban said. "Do not wait for consultation. Just take action."

World Bank President Jim Yong Kim admitted that the world was "behind the curve" in the fight against Ebola.