Ebola has returned to Africa, surfacing this time in the Democratic Republic of the Congo. As of Saturday, according to the World Health Organization, there have been 49 confirmed or probable cases of the hemorrhagic disease in the DRC, along with 25 deaths. Most have occurred in a hard-to-access area, but at least one is in the million-person city of Mbandaka, almost 100 miles down the Congo River from the original cases and a short distance to the DRC’s border with the Republic of Congo.

This outbreak marks the third surge in Ebola this decade, including a vast epidemic that took more than 11,000 lives between 2014 and 2016. By now, the response follows a predictable pattern. The WHO, Centers for Disease Control and Prevention, and Doctors Without Borders send in rapid-response teams. These teams set up treatment centers and ship in supplies—including, this time, the first doses of an experimental vaccine.

With luck, those emergency measures will control the spread of this outbreak. But there’s another emergency measure that won’t curb Ebola, and might even encourage it to spread: stopping people at national borders to see whether they carry the disease.

So far, Nigeria and Kenya have set up health stations at land crossings, ports, and airports to check the temperature of travelers whose trips began in the DRC. There are no reports yet of people being turned away if they are feverish, but their itineraries are recorded in case they need to be tracked down afterward. If this outbreak expands, such interruptions to travel could too; seven countries instituted border checks during a small outbreak last year.

Checking people at the border—or even closing borders entirely against travelers from an infected zone—feels intuitively right, an easy solution for keeping disease at bay. (During the 2014-16 epidemic, President Donald Trump—not yet a candidate at that point—called for grounding all flights from West Africa, and said that humanitarian medical personnel who contracted the disease should be left there to die.)

But researchers who have studied earlier border-crossing outbreaks say the checks amount to little more than political theater. They do little to curb the spread of a disease, but they are likely to apprehend uninfected travelers, slow down commerce, and most importantly, impede the delivery of relief supplies. In a worst-case scenario, health stops may cause infected people to sneak to border crossings where checks haven’t been set up, spreading disease as they go.

“Border screenings and border closures both come from the same place, which is a desire to be seen to be doing something,” says Alexandra Phelan, a doctoral candidate and adjunct professor at Georgetown Law and a contributor to Ebola’s Message, an examination of the 2014-16 epidemic. “They are a way for governments or politicians to communicate to their people that they are taking the most protectionist measures they can. They have the appearance of being strict and stringent, but it’s not actually possible to close yourself off from in a globalized world.”

SARS, which girdled the globe in roughly a week in 2003, was the first modern epidemic to prove how rapidly diseases can travel. By the time most governments realized the threat, the virus already had crossed their borders.

But that didn’t stop many nations from trying to identify the disease in travelers, at vast cost and little benefit. After Toronto suffered early SARS casualties, the Canadian government spent more than $7 million screening more than 1 million arriving airline passengers to protect against further incursions. But in an analysis done after SARS burned itself out that summer, infecting more than 8,000 people worldwide and killing 774, Canadian researchers found the extensive screening had not caught a single extra case of the disease.

Also that year, China screened 14 million travelers for SARS symptoms, and found 12 possibly infected people; Singapore checked 500,000 people and found none. Six years later, worried about the international movement of swine flu, Australia set up screening at all eight airports that receive international flights. Starting with the WHO’s declaration of an international health emergency and up to the end of flu season, the country checked more than 1.8 million people, and spotted 15,457 of them who might be ill. In the end, only 154 were possible cases of swine flu—and there’s no record of any of them passing on that relatively mild disease.

As Australian researchers pointed out afterward, the country’s program was resource-intensive: it required the purchase of fever scanners, and the hiring of scanner operators and public health nurses for every shift at every airport—costs that ate up money from elsewhere in public health.

The difficult reality of outbreaks is that as long as infected people feel well enough to travel, they are unlikely to look different from someone with a disease that doesn’t pose a threat. SARS patients were feverish; so were swine flu patients, and Ebola patients are as well—but so are people with colds and bronchitis during flu season, and with malaria and other diseases common in the areas where Ebola occurs. (The lone exception to this may be the dead disease smallpox; its pustules were so distinctive that epidemiologists could track down victims in strange villages just by describing the lesions.)

This means that while people with “safe” infections will be caught in a dragnet, people who could potentially spark outbreaks may slip through. That’s how Ebola came to the US in 2014, via a traveler from Liberia who wasn’t ill while he was traveling. He didn’t develop symptoms—and therefore wasn’t infectious—until after he arrived at the home of family living in Dallas. That traveler, Thomas Duncan, passed the disease to two nurses who treated him and who were not aware of the seriousness of his illness. He died; they survived.

Nigeria is on alert now because of Patrick Sawyer, a Liberian-American who brought Ebola to Nigeria in 2014, died there, and sparked an outbreak that killed eight others. Sawyer was already very ill when he traveled to Nigeria; it was later discovered that he had been under observation for possible Ebola in a Liberian hospital, checked himself out, and flew to Ghana and Togo before landing in Lagos.

If Sawyer had been stopped before leaving Liberia, Nigeria’s outbreak would not have happened. His story shows that border screening might be successful if it occurs at the start of a journey, instead of the end of one—that is, before people leave the place they fell ill. It’s possible that exit screening, as it’s called, prevented the international epidemic from being even larger than it was. On Oct. 5, 2014, the day the CDC disclosed the illness of Thomas Duncan in Dallas, the agency also said that its disease detectives and partners had identified 77 people who were visibly ill in airports in West Africa. Because the countries were screening passengers in airports, none of them were allowed on planes.

In a statement released Friday, the WHO encouraged health checks at departure instead of arrival, writing: “Exit screening, including at airports and ports on the Congo river, is considered to be of great importance; however, entry screening, particularly in distant airports, is not considered to be of any public health or cost-benefit value.”

There’s another message embedded in these stories. After Sawyer fell ill, Nigerian public health responded quickly, tracking down almost 900 people he crossed paths with to make sure no one passed on the disease. After Duncan’s illness was discovered, eight other people, all medical personnel, came to the United States with Ebola. All of them were identified before they left West Africa, and not one infected anyone else.

What was true for Nigeria and the United States ought to be true everywhere. The most important protection against a border-crossing disease is an alert, aggressive, fully funded public-health system. Until those exist everywhere, any country on either side of an airplane ride will be at risk.



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