Santa Fe Institute

Science for a Complex World: The mathematics of stopping Ebola

Nov. 25, 2014 11:51 a.m.

This column is the latest in the "Science in a Complex World" series written by Santa Fe Institute researchers and published in The Santa Fe New Mexican. This article appeared on November 23, 2014.

By Samuel V. Scarpino, Omidyar Fellow, Santa Fe Institute

Last July, a group of scientists from eight research groups around the country began holding weekly meetings to develop a mathematical understanding of the Ebola virus outbreak in West Africa. This league of mathematicians, computer scientists, epidemiologists and biologists was unusual not only because of its members’ diverse scientific backgrounds, but also because it included five researchers from the Santa Fe Institute.

These institute scientists provide an important perspective on disease transmission — specifically, emphasizing the need to piece together how the various factors affecting disease transmission interact to cause a large outbreak. This approach, which we call complex systems science, already has improved our understanding of the spread of infectious diseases, from SARS to the 2009 H1N1 influenza pandemic. I was humbled to be asked to join the discussions and eager to be able to offer a complex systems perspective to what was quickly becoming a global emergency.

At SFI, my colleagues and I are constructing mathematical models of Ebola transmission, incorporating many interacting factors that might be contributing to the outbreak. These models help inform the intervention decisions being made every day by public health officials. The first step in this process was to develop computer models of Ebola’s spread to look at its potential reach in West Africa and across the world. These models required us, as complexity scientists, to piece together a dizzying number of interconnected processes: the biology and evolutionary trajectory of the virus, the travel patterns of humans moving in and out of the afflicted countries, the behavioral practices of its victims, the health care infrastructure in West Africa and the potential role of various public health interventions.

This type of approach — where we seek a detailed understanding of how a complex set of factors interacts to result in a major event, such as an epidemic — is a hallmark of the Santa Fe Institute. For 30 years, we have been using this complex systems lens to look at wide-ranging issues in systems from the stock market to cities to influenza pandemics.

It has now produced novel insights about the Ebola outbreak. The most significant of these, perhaps, has been identifying a clear link between poverty and Ebola infection. To date, the Ebola virus has claimed the lives of more than 5,000 residents of Sierra Leone, Guinea and Liberia. These West African countries are among the world’s most impoverished; on average, more than half of all residents in each of these countries live below their nation’s poverty line. That the countries experiencing the largest Ebola outbreak on record are among the world’s most impoverished is, troublingly, not a coincidence.

The link between poverty and Ebola becomes more clear when you consider how poverty affects a country’s health care infrastructure. Sierra Leone, Liberia and Guinea have, on average, fewer physicians, nurses and hospital beds per capita than 95 percent of the world’s countries. This translates to around 300 physicians for a country of 6 million people, the average population of each of these three nations. Put another way, that’s one doctor per 20,000 residents. By analogy, in the United States, we would have to fire more than 98 percent, or around 750,000, of our physicians to achieve a doctors-to-people equivalent.

Despite the seemingly complex nature of the Ebola virus, an effective intervention to stop the disease and prevent additional large outbreaks is simple. Other African countries such as Nigeria and Uganda have only marginally more physicians, hospital beds and nurses than the afflicted regions in West Africa, yet this modest increase in health care infrastructure was enough for them to have succeeded in stopping Ebola in its tracks by using quick and effective case isolation and contact tracing to find exposed individuals before they became infectious.

The only way to prevent more Ebola cases from occurring in the United States and other countries is to stop the epidemic in West Africa. As a global community, this means accelerating the deployment of health care workers and increasing the health care capacity in all three countries. Achieving this will require international cooperation and money, certainly. But just as important, stopping Ebola will require us to enlist the support of the global population in delivering aid.

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Samuel V. Scarpino is an Omidyar Postdoctoral Fellow at the Santa Fe Institute. His primary research interests lie at the interface of evolutionary biology, operations research and epidemiology. His past work on disease surveillance, done in close collaboration with state and national public health agencies in the U.S., has led to substantive changes in surveillance practices. He holds a Ph.D. in integrative biology from The University of Texas at Austin and attended SFI’s Complex Systems Summer School in 2010.

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