The Ebola outbreak in West Africa kills seven out of 10 victims and new cases could hit 10,000 a week within two months if it is not brought under control, the World Health Organization has said.

The organization’s assistant director-general Dr Bruce Aylward said on Tuesday that the death rate was higher than the official 50 percent rate and that "a lot more people will die" if the West Africa outbreak was not stopped.

"What we're finding is 70 percent mortality," said Aylward, adding that he had a "working forecast" of 5,000 to 10,000 new cases a week by December to guide the international response.

"It's been running at about a thousand cases a week now for about three to four weeks," he said. "The labs sometimes can't keep up with the amount of specimens they're getting."

WHO figures released on Tuesday show 8,914 confirmed cases and a total of 4,447 people dead. However, the organization has said several times that the tallies are unreliable due to difficult recording conditions and workload.

Sierra Leone, Guinea and Liberia have been hardest hit.

"There are this many cases that we're aware of, this many deaths that have been reported to us, but that doesn't mean you divide one by the other and get how many this disease kills," Aylward said.

"To get that number, you need to take a bunch of people, follow them right through the course of their disease, and understand how many survive. That subset of people, who we know were sick, and we know their final outcome, what we're finding is 70 percent mortality, it's almost the exact same number across the three countries," he said.

Aylward said that the WHO needed to isolate 70 percent of cases within two months to contain the outbreak.

"Every time you isolate another patient, every time you have a safe burial, you're taking some of the heat out if this outbreak," said Aylward. "But this is Ebola. This is a horrible, unforgiving disease. You've got to get to zero."

In Berlin, a UN medical worker infected with Ebola in Liberia has died. The St Georg hospital in Leipzig said on Tuesday that the 56-year-old man, whose name has not been released, died overnight of the infection.

The man tested positive for Ebola on October 6, prompting Liberia's UN peacekeeping mission to place 41 other staff members under "close medical observation".

Meanwhile, the UN warned on Tuesday the world is failing to gain the upper hand against the deadly outbreak.

"Ebola got a head start on us," said Anthony Banbury, head of the UN Mission for Ebola Emergency Response.

"It is far ahead of us, it is running faster than us, and it is winning the race," the Briton told the UN Security Council in New York, by remote link from UNMEER headquarters in Accra.

"If Ebola wins, we the peoples of the United Nations lose so very much,' he said.

"We either stop Ebola now or we face an entirely unprecedented situation for which we do not have a plan," Banbury stressed.

PHOTO CAPTION

As Ebola continues to spread from through Liberia, an American charity worker, Katie Meyler, is desperately trying to lend a hand. With the Liberian health care system stretched to the limit, Meyler's charity is using a donated ambulance to help rush victims to care centers. Debora Patta reports.

Aljazeera