Ebola virus cases in West Africa are rising faster than the ability to contain them, the World Health Organization says, as experts warn that the exponential rise could become a worldwide disaster.

The death toll has risen to more than 2,400 people out of 4,784 cases, WHO director general Margaret Chan told reporters at the UN health agency’s headquarters in in Geneva on Friday, noting the figures could be an underestimate.

"In the three hardest hit countries, Guinea, Liberia and Sierra Leone, the number of new patients is moving far faster than the capacity to manage them. We need to surge at least three to four times to catch up with the outbreaks," Chan said.

She called for urgent international support in the form of doctors, nurses, medical supplies and aid to the worst-affected countries.

Health-care workers have been infected with Ebola while treating patients in West Africa. Almost half of the 301 health-care workers who have developed the disease have died.

Chan welcomed Cuba’s announcement that it will send 165 health-care workers to fight the outbreak, but added that at least 500 doctors from abroad are needed.

A doctor, wearing protective gear, takes part in a drill with a dummy to demonstrate the procedures of handling a patient afflicted with the Ebola virus, in Hong Kong in early September. (Tyrone Siu/Reuters)

An infectious disease expert warned in Friday’s New York Times that "the Ebola epidemic in West Africa has the potential to alter history as much as any plague has ever done."

Michael Osterholm is the director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

Ebola spreads through direct contact with bodily fluids, but Osterholm raised a possibility that he said virologists are loath to discuss openly but consider behind closed doors: the prospect that the Ebola virus could mutate to become transmissible through the air.

Osterholm cites a 2012 study by researchers at the National Microbiology Laboratory in Winnipeg that showed the Ebola Zaire strain behind West Africa’s outbreak could spread by the respiratory route between pigs and monkeys.

The key to containing the outbreak, Osterholm stressed, is to beef up efforts to stop the spread of the virus.

'Unprecedented' outbreak needs response to match

To that end, he suggested that the United Nations take over the position of "command and control" to direct the efforts of medical, public health and humanitarian aid from countries and non-governmental groups.

A woman mourns the death of a family member in Monrovia, Liberia, earlier this week. The World Health Organization warns that the country already accounts for half of the more than half of the 2,000 deaths across West Africa from the virus. (Zoom Dosso/AFP/Getty)

"If we wait for vaccines and new drugs to arrive to end the Ebola epidemic, instead of taking major action now, we risk the disease's reaching from West Africa to our own backyards," he concluded in a commentary titled, "What We’re Afraid to Say About Ebola."

Meanwhile, an editorial in Eurosurveillance, published by the European Centre for Disease Prevention and Control, said it was hard to track an outbreak with exponential growth in case numbers.

"Ebola cannot be ignored in the hope it will burn itself out," Peter Piot, one of the scientists who first identified the Ebola virus in 1976, and his colleague Adam Kucharski, said in their editorial. Piot is now director of the London School of Hygiene and Tropical Medicine.

Stronger control measures are needed to stop transmission, Piot and Kucharski said.

A modelling study published in Eurosurveillance projects that, if the growth in cases continues at its current pace, under a worst-case scenario there could be another 77,000 to 277,000 cases by the end of the year.

"Many of the issues currently facing West Africa — from lack of trust in health authorities to poor infection control — have surfaced before, and have been overcome. However, the current outbreak is unprecedented both in size and scale. It will require a response to match," they concluded.

Darren Tosh is project director of Samaritan's Purse Canada. One of the group's U.S. missionaries, Dr. Kent Bradly, was infected with Ebola in West Africa and has recovered.

"The epidemiological models show this Ebola outbreak to be taking tens of thousands of lives that we've yet to even project," Tosh said. "We can see that this epidemic is not slowing down and we just try to continue to ramp up as much as we can."