"The closer you get to zero, the harder the job."

That's according to , who heads the U.N.'s effort against Ebola. In a new report, the agency says that while health workers have been making progress in containing the outbreak in West Africa, it will take $1.5 billion over the first half of 2015 to bring the number of cases down to zero. And the effort will require more than 67,000 national and international health care workers and experts.

"The control effort has to concentrate on getting to the very last case," Nabarro says. "Because if you don't completely eliminate it, [the virus] can always come back and cause a flare up."

Over the past months, the number of new Ebola cases in the region has been plummeting, with 99 reported for the last week of January — the lowest since June 2014. But a jump to 124 new cases this week shows that Ebola remains a threat.

Some of the money is already in place. Since September, the international community and private donors have given $482 million to groups like the World Health Organization, UNICEF and the World Food Program to keep their Ebola-related programs running in 2015.

The money would enable contact tracers and burial teams to reach possible Ebola victims in 63 hotspots — many of them deep in the jungle. "You have to switch from just offering to treatment or burying [as many] bodes in a safe way as you can to a situation where you are trying to identify every single chain of transmission of the disease," Nabarro says.

To do that, the U.N. needs to make sure the health care workers have the right transportation — cars, helicopters — and "fantastic" communication and mobile technology to quickly get information back to labs and treatment centers. And this has to be done "in a part of the world which has virtually no electricity," he tells Goats and Soda.

Part of the money will also help the three hardest-hit countries rebuild their health infrastructure to provide basic care and prevent additional outbreaks in the future.

"We hope we don't need it all and we'd happily repay whatever we don't use," Nabarro says. "But we need enough so we're not scrambling around and having to cut back on our operations." And the donations have been coming in. In January alone, he adds, the U.N. has received more than $100 million in donations, bringing the total amount needed down to $900 million.

"It's a huge operation," he says. "And it's expensive. But it has to be done."

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