Militants of Islamic State are seen before explosion of air strike on Tilsehir hill near the Turkish border village Yumurtalik in Sanliurfa province, Oct. 23, 2014.
BULENT KILIC—AFP/Getty Images
December 4, 2014 10:51 AM EST

As images of brutal beheadings and dying plague victims compete for the world’s shrinking attention span, it is instructive to compare the unexpected terrors of the Islamic State of Iraq and Greater Syria (known as ISIS or ISIL) and Ebola. In October, the U.N. High Commissioner for Human Rights pointed out that “the twin plagues of Ebola and ISIL both fomented quietly, neglected by a world that knew they existed but misread their terrible potential, before exploding into the global consciousness.” Seeking more direct connections, various press stories have cited “experts” discussing the potential for ISIS to weaponize Ebola for bioterrorist attacks on the West.

Sensationalist claims aside, questions about similarities and differences are worth considering. Both burst onto the scene this year, capturing imaginations as they spread with surprising speed and severity. About Ebola, the world knows a lot and is doing relatively little. About ISIS, we know relatively little but are doing a lot.

In the case of Ebola, the first U.S.-funded treatment unit opened on Nov. 10—more than eight months after the epidemic came to the world’s attention. The U.S. has committed more than $350 million and 3,000 troops to this challenge to date. To combat ISIS, President Obama announced on Nov. 7 that he would be sending an additional 1,500 troops to Iraq to supplement his initial deployment of 1,500. And he has asked Congress for a down payment of $5.6 billion in this chapter of the global war on terrorism declared by his predecessor 13 years ago and on which the U.S. has spent more than $4 trillion so far.

Over recent centuries, medicine has made more progress than statecraft. It can be useful therefore to examine ISIS through a public-health lens. When confronting a disease, modern medicine begins by asking: What is the pathogen? How does it spread? Who is at risk? And, informed by this understanding, how can it be treated and possibly prevented?

About Ebola, we know the answers to each. But what about ISIS?

Start with identification of the virus itself. In the case of Ebola, scientists know the genetic code of the specific virus that causes an infected human being to bleed and die. Evidence suggests that the virus is animal-borne, and bats appear to be the most likely source. Scientists have traced the current outbreak to a likely animal-to-human transfer in December 2013.

In the case of ISIS, neither the identity of the virus nor the circumstances that gave rise to it are clear. Most see ISIS as a mutation of al-Qaeda, the Osama bin Laden–led terrorist group that killed nearly 3,000 people in the attacks on the World Trade Center and Pentagon in September 2001. In response to those attacks, President George W. Bush declared the start of a global war on terrorism and sent American troops into direct conflict with the al-Qaeda core in Pakistan and Afghanistan. In the years since, the White House has deployed military personnel and intelligence officers to deal with offshoots of al-Qaeda in Iraq (AQI), Yemen (AQAP), Syria (al-Nusra) and Somalia (al-Shabab).

But while ISIS has its roots in AQI, it was excommunicated by al-Qaeda leadership in February. Moreover, over the past six months, ISIS has distinguished itself as a remarkably purpose-driven organization, achieving unprecedented success on the battlefield—as well as engaging in indiscriminate violence, mass murders, sexual slavery and apparently even attempted genocide.

Horrifying as the symptoms of both Ebola and ISIS are, from an epidemiological perspective, the mere emergence of a deadly disease is not sufficient cause for global concern. For an outbreak to become truly worrying, it must be highly contagious. So how does the ISIS virus spread?

Ebola is transmitted only through contact with infected bodily fluids. No transfer of fluids, no spread. Not so for ISIS, where online images and words can instantly appear worldwide. ISIS’s leadership has demonstrated extraordinary skill and sophistication in crafting persuasive messages for specific audiences. It has won some followers by offering a sense of community and belonging, others by intimidation and a sense of inevitable victory, and still others by claims to restore the purity of Wahhabi Islam. According to CIA estimates, ISIS’s ranks of fighters tripled from initial estimates of 10,000 to more than 31,000 by mid-September. These militants include over 15,000 foreign volunteers from around the globe, including more than 2,000 from Europe and more than 100 from the U.S.

Individuals at risk of Ebola are relatively easy to identify: all have come into direct contact with the bodily fluids of a symptomatic Ebola patient, and almost all these cases occurred in just a handful of countries in West Africa. Once symptoms begin, those with the virus soon find it difficult to move, much less travel, for very long undetected.

But who is most likely to catch the ISIS virus? The most susceptible appear to be 18- to 35-year-old male Sunni Muslims, among whom there are many Western converts, disaffected or isolated in their local environment. But militants’ individual circumstances vary greatly, with foreign fighters hailing from more than 80 countries. These terrorists’ message can also inspire “lone wolf” sympathizers to engage in deadly behavior thousands of miles from any master planner or jihadist cell.

In sum, if Ebola were judged as a serious threat to the U.S., Americans have the knowledge to stop it in its tracks. Imagine an outbreak in the U.S. or another advanced society. The infected would be immediately quarantined, limiting contact to appropriately protected medical professionals—thus breaking the chain of infection. It is no surprise that all but two of the individuals infected by the virus who have returned to the U.S. have recovered and have not infected others. Countries like Liberia, on the other hand, with no comprehensive modern public-health or medical system, face entirely different challenges. International assistance has come slowly, piecemeal and in a largely uncoordinated fashion.

Of course, if ISIS really were a disease, it would be a nightmare: a deadly, highly contagious killer whose identity, origins, transmission and risk factors are poorly understood. Facing it, we find ourselves more like the Founding Fathers of the U.S., who in the 1790s experienced seasonal outbreaks of yellow fever in Philadelphia (then the capital of the country). Imagining that it was caused by the “putrid” airs of hot summers in the city, President John Adams and his Cabinet simply left the city, not returning until later in the fall when the plague subsided. In one particularly virulent year, Adams remained at his home in Quincy, Mass., for four months.

Not until more than a century later did medical science discover that the disease was transmitted by mosquitoes and its spread could be stopped.

We cannot hope to temporarily escape the ­“putrid” airs of ISIS until our understanding of that scourge improves. Faced with the realities of this threat, how would the medical world suggest we respond?

First, we would begin with humility. Since 9/11, the dominant U.S. strategy to prevent the spread of Islamic extremism has been to kill its hosts. Thirteen years on, having toppled the Taliban in Kabul and Saddam Hussein in Baghdad, waged war in both Iraq and Afghanistan, decimated the al-Qaeda core in Pakistan and Afghanistan and conducted 500 drone strikes against al-Qaeda affiliates in Yemen and Pakistan, and now launched over 1,000 air strikes against ISIS in Iraq and Syria, we should pause and ask: Are the numbers of those currently infected by the disease shrinking—or growing? As former Secretary of Defense Donald Rumsfeld once put it: Are we creating more enemies than we are killing? With our current approach, will we be declaring war on another acronym a decade from now? As we mount a response to ISIS, we must examine honestly past failures and successes and work to improve our limited understanding of what we are facing. We should then proceed with caution, keeping in mind Hippocrates’ wise counsel “to help, or at least, to do no harm.”

Second, we would tailor our treatments to reflect the different theaters of the disease. Health care professionals fighting Ebola in West Africa face quite different challenges of containment, treatment and prevention than do their counterparts dealing with isolated cases in the Western world. Similarly, our strategy to “defeat and ultimately destroy” ISIS in its hotbed of Iraq and Syria must be linked to, but differentiated from, our treatment for foreign fighters likely to “catch” the ISIS virus in Western nations. While continuing to focus on the center of the outbreak, the U.S. must also work to identify, track and—when necessary—isolate infected individuals within its borders.

Just as Ebola quarantines have raised ethical debates, our response to foreign fighters will need to address difficult trade-offs between individual rights and collective security. Should citizens who choose to fight for ISIS be stripped of their citizenship, imprisoned on their return, or denied entry to their home country? Such a response would certainly chill “jihadi tourism.” Should potential foreign fighters be denied passports or have their travel restricted? How closely should security agencies be allowed to monitor individuals who visit the most extremist Salafist websites or espouse ISIS-friendly views? Will punitive measures control the threat or only add fuel to radical beliefs?

Finally, we should acknowledge the fact that for the foreseeable future, there may be no permanent cure for Islamic extremism. Against Ebola, researchers are racing toward a vaccine that could decisively prevent future epidemics. But the past decade has taught us that despite our best efforts, if and when the ISIS outbreak is controlled, another strain of the virus is likely to emerge. In this sense, violent Islamic extremism may be more like the flu than Ebola: a virus for which we have no cure, but for which we can develop a coherent management strategy to minimize the number of annual infections and deaths. And recalling the 1918 influenza pandemic that killed at least 50 million people around the world, we must remain vigilant to the possibility that a new, more virulent and contagious strain of extremism could emerge with even graver consequences.

Allison is director of the Belfer Center for Science and International Affairs at Harvard’s John F. Kennedy School of Government

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