MONROVIA—Hans Rosling is a global health celebrity, a former head of the Division of Global Health at the Karolinska Institute in Stockholm whose riveting lectures have made him a star of TED talks, and a fixture of the World Economic Forum in Davos, Switzerland. But since 20 October, he has occupied room 319 of Liberia's Ministry of Health & Social Welfare, a large yellow building not far from the Atlantic Ocean. Working alongside the country's head of Ebola surveillance, Luke Bawo, he is helping the ministry make sense of the largest Ebola outbreak ever recorded.

Rosling has come without any affiliation, which he says helps him stay independent. “He just walked into the office and introduced himself,” Bawo says.

He feels bad about not coming earlier. Ebola arrived in Liberia from Guinea in March, then spread south to Monrovia, where it exploded in August. Hospitals were closed and Ebola treatment units were overwhelmed. “I thought the Ebola outbreak could be stopped locally,” Rosling says. “I just wasn’t smart enough.” (He also felt he was too old to work in a treatment unit.)

When he saw the epidemic curve go up in Sierra Leone and down in Liberia in October, he was skeptical, and he decided to find out firsthand what was happening. He canceled his lectures and contacted the Liberian government. “I’m not a virologist and I’m not a clinician, but I have considerable experience investigating messy epidemics in poor parts of Africa,” he says.

A quarter-century ago, he faced a threat that seemed even more terrifying than Ebola. In August 1981, Rosling was working as a district medical officer in northern Mozambique when he sat in front of a line of 30 women and children whose legs had become paralyzed over the past month. "I had this big neurology book, and their disease did not exist in that book,” Rosling says. A South African submarine had been spotted in a nearby bay a few weeks earlier. “It was fully possible that it was biological warfare.”

When he came home that evening, he told his wife to take their kids and drive them to a safer place a few hours away. He didn't sleep the next 48 hours. “When you face a disease that may be infectious, 98% of your intellectual capacity becomes blocked. You become so scared, thinking you will die, thinking you may be crippled, thinking about your children.” It took 2 weeks before it became clear the affliction wasn't contagious. (Now called konzo, it's caused at least in part by toxic compounds in cassava roots.) A group of Italian nuns helped Rosling overcome his fears. "I don't think I could have done this without them," he says.

The experience left Rosling with a cool approach to health crises and a keen sense of what it takes to fight a disease in one of the poorest parts of the world. Soon after he arrived in Monrovia, he became convinced that the Liberian decline is real, driven in large part by changes in behavior that reduce the risk of infection. Liberia now reports only some 10 new cases a day. That's good news, but it also presents big new challenges. While Ebola was the main cause of death, safe burials were essential. Now that new infections are less common, people could in principle resume traditional funeral practices, which include contact with the body, for deaths not due to Ebola. But spreading that message could cause people to drop their guard with Ebola victims, too, leading to new infections. “Any decision will have many complicated consequences,” Rosling says.

Rosling learned that lesson, too, in the konzo outbreak. Because he was initially unable to rule out an infectious disease, the Mozambican government set up a roadblock to stop the disease from spreading. A group of people took a boat along the coast to evade the blockade, and it sank. "I have stood there and seen the bodies of 18 women and children who drowned because of that roadblock,” he says. "That stays with you. Eighteen bodies of people you killed.”

After he arrived in Monrovia, Rosling started by doing simple things, such as proofreading the ministry's epidemiological reports, which he says nobody had time for. He changed an important detail in the updates: Rather than listing "0 cases" for counties that had not reported any numbers—which could be misleading—he left them blank. Next, he tackled the problem behind the missing data. Some health care workers couldn't afford to call in their reports, because they were paying the phone charges themselves; Rosling set up a small fund to pay for scratch cards that gave them airtime.

One of Hans Rosling’s recent "Factpods" on YouTube discussed the spread of Ebola in West Africa.

Now, he's focusing on how to get the number of new cases down to zero. That means finding every single case, tracing that patient’s contacts, and isolating all of those who show symptoms—a huge challenge in a country where many villages are hours away from a road, Ebola symptoms like diarrhea and fever are common, and the fear of the deadly virus drives some contacts to skip town and seek out a traditional healer. “We have to make a meticulously perfect system work in a country where such a system cannot exist,” he says. “This is the biggest intellectual challenge I have participated in in my life.”

On a whiteboard in his office, Rosling has drawn a complicated flow chart to show how the information about patients and their contacts moves through the system. Data are lost at several steps. Some people die on the way to the hospital; others give different ages or names at different points. Rosling’s aim is to know how many of the newly discovered Ebola patients are already on one of the contact lists. But so far he has been struggling even to find out what county every patient is from.

Others on the front lines welcome Rosling's help. Kevin De Cock, who leads the U.S. Centers for Disease Control and Prevention (CDC) field team in Liberia, calls him “an eminent epidemiologist with immense African experience. He provides strong technical and intellectual input.” Bawo says he admires Rosling's commitment but worries that he's overstretching himself. “He is welcome to stay, but I make it my business that he takes one day off a week,” Bawo says. “Every Sunday I don’t call him, he does not call me, and I do not want him to send me an e-mail.”

Rosling says he's tired of the portrayal of Africa as a continent of incompetence, superstition, and rampant corruption. “I am astonished how good people are that I work with here, how dedicated, how serious,” he says. When The New York Times reported that governmental infighting was hampering the Ebola response, Rosling tweeted: “Don McNeil misrepresents Liberia’s EBOLA-response to win the MOST INCORRECT ARTICLE ABOUT EBOLA AWARD.” His self-assurance and impatience with opinions he disagrees with can grate on others. “I find him quite irritating,” says one Western colleague. “Mostly because he turns out to be right about most things.”

Rosling is critical of Western nations' response to the crisis. Whereas experts from elsewhere in Africa have come as colleagues and stayed for long periods of time, for instance, agencies like CDC replace their staff every few weeks, which Rosling says hampers continuity. (CDC is like Cuba, Rosling says: “Amazing people, bad system.") The U.S. military won’t transport patients or even blood samples in their helicopters, he adds: “Welcome to the continent of less superstition.”

Rosling eventually wrote his Ph.D. thesis about the konzo outbreak, helped set up the Swedish chapter of Doctors Without Borders, and became a professor of global health at the Karolinska Institute, where he retired in 2012. His talks still garner "obscene fees," he says—some $600,000 annually—which he uses to finance the Gapminder Foundation, a nonprofit he set up to bring development statistics to a broad audience. His talks have been viewed by millions, 200,000 people follow him on Twitter, and he has rich and powerful fans. “Mark Zuckerberg called me yesterday,” he says at one point, to ask how his money could help fight Ebola.

Rosling's 2006 TED talk debunked myths about the developing world.

In his talks, which feature dazzling graphics, Rosling is fond of emphasizing that most people's view of the world is wrong. He often asks how many children get the standard childhood vaccinations—20%, 50%, or 80%? Most people answer 20%, but it's 80%. “The problem is that the education systems in North America and Europe and the media have not conveyed a fact-based view of the world.”

Similarly, many people lump everything from Turkey to Somalia together as the developing world, blurring the differences between middle-income countries and those dominated by extreme poverty. He likes to say that 1.5 billion people have a light bulb and a washing machine, 4 billion have only the light bulb, and about 1.5 billion have neither. The populations of Liberia, Guinea, and Sierra Leone mostly fall into the last category, he says. “And that is one reason we can have such a huge Ebola outbreak here.”

Eradicating extreme poverty should be a top priority, says Rosling, who has been critical of programs that focus on a single disease, such as the multibillion-dollar initiative to eradicate polio. That has put him at odds with Bruce Aylward of the World Health Organization (WHO), who heads the campaign. Now, Aylward is also in charge of WHO’s Ebola response, but in this case, there's no disagreement: “Ebola is different,” Rosling says, adding that Aylward gave him important guidance. Aylward praises Rosling as “great added value."

Although he does not come into contact with Ebola patients, Rosling had one moment when his fear of infectious diseases returned. One night in his Monrovia hotel, he developed diarrhea. He skipped dinner and locked himself up in his room. “I had to plan. Should I tell my family? Should I not?” he says. He decided to take his temperature every 2 hours and monitor himself for additional symptoms. “But I did finish my report before I went to bed.” He felt fine the next morning, and he's not planning to return to Sweden anytime soon. “I canceled Christmas with the family," he says. "But I hope to be home for Midsummer’s Eve.”

*The Ebola Files: Given the current Ebola outbreak, unprecedented in terms of number of people killed and rapid geographic spread, Science and Science Translational Medicine have made a collection of research and news articles on the viral disease freely available to researchers and the general public.