“Seven to one!” our new friend smiled. “Seven! Unbelievable.” We laughed along, recounting Brazil’s incredible World Cup defeat. It was early July, and we were waiting to board the crowded ferry to cross the bay from Freetown, Sierra Leone. At the time, the World Cup was one of two topics all strangers were discussing in the busy port city and throughout the country. The other topic was Ebola.
Despite the growing attention, in many ways life trudged on as normal for most Sierra Leoneans. But whispers of the virus — where it had been detected? how do you get it? how it had spread? where is it going next? — were heard everywhere. In the city of Kenema, where we worked to understand how the virus was changing, these whispers were more pervasive. Kenema was at the center of the outbreak, and it seemed unlikely that the available resources could contain its spread for very long. Fear of the outbreak was smoldering
Today, as the fire of Ebola rages in parts of West Africa, sparks have inevitably begun to land around the globe. The virus has now entered Spain and the United States and infected people in both places. Now the water cooler talk here has turned to baseball playoffs and Ebola.
The American public is experiencing many of the same anxieties that we witnessed in July in Sierra Leone. Many people are understandably concerned about how the virus is transmitted and where it will go next with a mixture of denial and dread. Information and misinformation spread differently in the United States than in Sierra Leone, but it is not hard to find firebrands here, too, questioning Ebola’s existence and means of spread. It is important that we directly address key questions and anxieties, including the pervasive concern that Ebola will soon go airborne.
When it comes to how you catch Ebola, it is important to remember that, compared to many other human pathogens, the way this disease spreads is not very mysterious. Ebola is spread by contacting infected body fluids, such as blood, feces, sputum, and vomit, of someone with active symptoms. This mechanism requires close contact — within a few feet — with the contagious person.
Airborne viruses, in contrast, circulate for extended periods of time and over long distances in tiny particles in the air, which can be inhaled and lead to illness. Ebola virus has never been observed to spread this way.
In nearly every case in which the effort has been made to trace transmission of the disease, we have been able to identify the sick person through whom an Ebola patient became infected. Those at highest risk of contracting Ebola are health care workers and close household members. By interviewing patient families, health care workers, and personal contacts, we can definitively determine in retrospect how the virus passed from one person to another.
In contrast, for airborne pathogens like seasonal influenza and measles, contact tracing is considerably more challenging. If you catch the flu, you often cannot backtrack and determine who gave it to you. Because these viruses spread by small aerosolized particles, they can linger in the air, and much less direct contact is needed to spread the disease. If Ebola were airborne, the Dallas patient would likely have infected many others not known to have been in close contact.
Even though contact tracing is straightforward for Ebola, the bar for understanding transmission has been raised considerably. We want to know not just whom the virus came from, but what specific action caused the infection. Was protective equipment not taken off correctly, or was a surface not fully disinfected? These are important questions to investigate for improving safety precautions, but if we cannot immediately answer them, it does not mean that we do not know how Ebola is spread or that it has mutated to spread in a new way.
We have to recognize that we already have the most powerful information for controlling the spread of disease: knowing who spread the virus to whom. Contact tracing and testing are critical to controlling Ebola. Nigeria recently contained the spread of Ebola following the introduction of an infected traveler, in large part through a committed effort to diagnostic testing and contact tracing. After overcoming early challenges much like America’s, Nigeria through successful coordination was able to stop an outbreak from spreading among the 21 million people of Lagos.
The success in Nigeria was possible, and can be in the United States, because the circumstances are fundamentally different from what Sierra Leone faced. Sierra Leone shares a porous border with two countries already entrenched in an epidemic. The outbreak began with 14 people infected with what turned out to be two distinct versions of the virus. By the time the first case was detected in a diagnostic lab three hours from the site, the outbreak had already been spreading across the country. In the United States, like in Nigeria and Senegal, we are positioned to stop the virus if we focus on diagnostics and contract tracing.
That is not to say that the virus could not change. As the virus makes new copies of itself it occasionally makes errors. The vast majority of changes are irrelevant or even harmful to the virus, but a small number may make the virus more fit for its environment. Yet seismic changes, such as a virus altering its transmission mode in a blink of evolutionary time, have never been seen, and are extremely unlikely now.
Nonetheless, any change is one change too many. Rather than fear unlikely and unpredictable changes, we need to stop them by stopping the virus’ spread. We should focus our attention on containing the virus by methods that we know work. Effectively testing and tracing contacts for Ebola patients requires an enormous commitment of personnel and resources to interview all suspected contacts and conduct tests. If we fall behind tracing and testing for the virus, we will lose track of where it is, as has occurred at times in parts of West Africa.
Back in July, at the end of our journey in Sierra Leone, we encountered a roadblock. After our ferry crossed the bay to Freetown, the many vehicles and hundreds of passengers on board began to quickly file down a ramp to shore. One of the exiting vans misjudged the angle of the ramp and ran aground, becoming completely stuck and trapping all of the vehicles remaining on the ferry.
At first, the driver attempted to free his van by himself, while others simply filed past. Soon though, a crowd gathered to lend a hand.
After several failed attempts, the group finally reached a clever solution to free the van. A team unloaded all of the goods to reduce its weight, and then chained the van to another large truck still aboard the boat. The second truck towed the van back up the ramp, to re-exit from a better angle. Simple teamwork, coordination, and creative thinking solved the problem.
The van was free, everyone could continue on his or her way, and for a moment life returned to normal.
Nathan Yozwiak is an infectious disease researcher at Harvard University and the Broad Institute. He works in Pardis Sabeti’s lab, which has been studying Lassa fever in Nigeria and Sierra Leone since 2008 and has also responded to the 2014 Ebola outbreak.