A second health worker in Texas has tested positive for Ebola, US officials said Wednesday, in a new contamination far from the west African heart of an epidemic that the UN warns is "winning the race".

Like the first, the second infection on US soil concerned a caregiver for a Liberian Ebola patient who died at a Dallas hospital earlier this month.

The worker came down with a fever on Tuesday and was isolated at the hospital right away, amid dire predictions that thousands of new infections were possible in the worst-hit west African countries before year's end.

"Health officials have interviewed the latest patient to quickly identify any contacts or potential exposures, and those people will be monitored," the Texas Department of State Health Services said.

The Centers for Disease and Prevention (CDC) said the positive test came from a preliminary analysis and that it was carrying out its own test to confirm the result.

Anthony Fauci, head of the National Institute for Allergy and Infectious Diseases, called the second infection "unacceptable."

The worst Ebola outbreak on record of has claimed 4,447 lives, out of 8,914 recorded cases since the start of the year, most of them in Liberia, Sierra Leone and Guinea.

"Ebola got a head start on us," Anthony Banbury, head of the UN Mission for Ebola Emergency Response, told the United Nations Security Council by remote link from Ghana Tuesday.

"It is far ahead of us, it is running faster than us, and it is winning the race," he said. "We either stop Ebola now or we face an entirely unprecedented situation for which we do not have a plan."

The World Health Organization said Tuesday the infection rate could reach 10,000 a week in a worst-case scenario.

WHO assistant director general Bruce Aylward, who described the figures as a working forecast, said the epidemic "could reach 5,000 to 10,000 cases per week by the first week of December."

US President Barack Obama was to participate in a video conference with his British, French, German, and Italian counterparts Wednesday to discuss the global response to the epidemic.

The leaders' talks came as British troops began loading a civilian-staffed military ship that will set sail for Sierra Leone this week to help in efforts to contain the outbreak.

As governments considered new crisis steps, Facebook co-founder Mark Zuckerberg announced a $25 million donation to the US Centers for Disease Control Foundation to help efforts to contain the epidemic.

'Hellish situation'

Liberian health workers late Tuesday ended a two-day strike to secure risk pay for Ebola, saying they put their country's needs first following global appeals to end the protest.

Ninety-five Liberian health workers have died so far in the epidemic and their colleagues were seeking compensation for the risk of dealing with Ebola, which spreads through contact with bodily fluids and for which there is no vaccine or widely available treatment.

In the capital Monrovia, a hospital patient described scenes of desolation on local radio, with sick people climbing over a fence to escape after being deserted by striking staffers.

"One of our colleagues died because he was bitten by a patient," said Alphonso Wesseh, a health worker who joined the strike.

"We are in a hellish situation."

Liberia's presidency said that the United States was set to give the country $5 million (four million euros) to pay health care workers.

Outside west Africa, medical staff have also been on the frontline of the crisis, with at least two cases of contamination reported despite safety protocols.

Both of the Texan health workers infected had cared for Ebola sufferer Thomas Eric Duncan, who is thought to have contracted the disease while still in Liberia, and who died on October 8.

The first, nurse Nina Pham, said she was "doing well", but authorities warned 76 workers may have been exposed during the patient's 10-day stay in the hospital.

CDC head Thomas Frieden said this week a "breach in protocol" led to Pham's infection.

Nurses have complained they were given little guidance on how to handle an Ebola case.

The first time Duncan came to the hospital he was sent back home, said a representative of National Nurses United in a phone conference.

When Duncan returned a few days later, feverish and visibly ill, he was made to sit for hours in a public waiting area, nurses said.

There were no guidelines on how to discard the Liberian patient's soiled towels and linens, they added.

"What happened there, regardless of the reason, is not acceptable," Fauci said.

"It is not acceptable that two nurses taking care of a person, because of their exposure... were infected," he said on MSNBC television.

In Spain, the nurse Teresa Romero, 44 -- thought to have caught Ebola while treating an elderly missionary infected in Sierra Leone -- was said to be in a stable condition.

In Germany, however, a 56-year-old Sudanese doctor who had worked as a UN volunteer in Liberia died of Ebola late Monday.