In 2001, not long after the 9/11 attacks, a mysterious spate of anthrax attacks by mail killed five people and sickened 17. What the FBI calls “the worst biological attacks in U.S. history” led to concerns that bioterrorists might weaponize other globally deadly diseases, like smallpox.
The sudden emergence of a highly infectious novel coronavirus in late 2019 has reminded us of a sobering fact: Nature is the ultimate bioterrorist. It’s the one we should fear the most. An unknown virus that once existed only in nature quietly entered a major city in China sometime before the end of 2019 and then spread rapidly around the world. As we write this, SARS-CoV-2, the virus that causes Covid-19, has already killed nearly 860,000 people.
As the outbreak began, there was immediate speculation about the origins of the virus. Initial theories considered emerging viruses in wild animals sold for human consumption in a wet market in Wuhan. That turned out to be an unlikely origin. The legitimate quest for the source of the pandemic was then quickly overwhelmed by theories that were inconsistent with known facts about an accidental release of a novel coronavirus from a Chinese virology lab.
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It’s imperative that we return to a fact-based consideration of the origins of Covid-19. One day this pandemic will end. But as we and several colleague wrote recently in the American Journal of Tropical Medicine and Hygiene, another one could soon begin if we don’t start focusing on what we know about the source of this and other potentially emerging viruses, and use these insights to prepare for the many other formidable threats brewing in nature.
Pandemics aren’t new. As one of us (D.M.M.) wrote with our colleague Dr. Anthony Fauci in the September issue of Cell, Covid-19 is at least the seventeenth pandemic caused by an emerging disease since the so-called Plague of Athens began in 430 BCE.
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For years, scientists had been predicting the inevitability of something like Covid-19. In the wake of the spread of severe acute respiratory syndrome (SARS) in 2002 and 2003, which was also caused by a coronavirus, scientists focused on the considerable reservoir of coronaviruses lurking in bats around the world. In 2007, one scientific group warned, “The presence of a large reservoir of SARS-CoV-like viruses in horseshoe bats … is a time bomb. The possibility of the re-emergence of SARS and other novel viruses … should not be ignored.”
Unfortunately, scientists such as these became modern-day Cassandras, ignored until their terrible predictions came true.
Scientists studying SARS and the 2012 emergence of Middle East respiratory syndrome (MERS), another disease caused by a bat coronavirus, discovered a key fact: Many bat coronaviruses are naturally suited for causing infections in humans and in other animals. This is because of something infectious disease researchers call host switching, also known as a spillover event. It’s a genetic change in a pathogen or parasite that allows it to live in a new host — in this case, switching from bats to humans.
After the SARS outbreaks — but long before Covid-19 — bat-to-human transmissions of SARS-like coronaviruses were detected in China, perhaps representing pandemic near-misses.
Today, the genetic sequence of SARS-CoV-2 indicates that its genome is 96% identical to certain coronaviruses found in wild bats. But the exact path the virus traveled as it switched from a bat host to a human host is not yet completely understood.
Several years ago, scientists identified a bat coronavirus “hot spot” in a vast contiguous area that includes Laos, Myanmar, Vietnam, and parts of south and southwest China. Disease experts also pointed to numerous ways these bat coronaviruses could jump to humans: cave exploration and bat tourism; wet markets that sell and butcher live animals; the growth of supply chains dedicated to selling wild animals for human consumption; destructive land management practices; and more.
While the detective work continues, it’s clear that we have had ample evidence for more than a decade that bat coronaviruses pose a major risk of causing a pandemic. The key issue now is to learn from our failure to recognize and act on these warning signs.
It can be helpful to put the existential threat of pandemics into context. The horrific bombings of Hiroshima and Nagasaki in 1945 killed somewhere between 110,000 people and 210,000. In 1918, 50 million died of influenza. Nothing on the typical radar screen of national security threats comes close to pandemic threats.
Today, we have international agencies, programs, treaties, and agreements dedicated to preventing nuclear wars. At the very least, the threat of infectious disease outbreaks exploding into pandemics and keeping tabs on emerging viruses deserves this same level of attention, investment, and international cooperation.
For starters, significant increases in bat coronavirus surveillance and research are urgently needed. This important work, which has languished, should be greatly expanded, and we should encourage scientists working in China and other hot-spot countries to join international research and surveillance partnerships.
Strengthening basic public health measures, including hygiene and sanitation in all countries, can also make us more secure. Emerging viruses should not find ready pathways to facilitate their spread. A stronger global public health infrastructure is also needed to respond quickly and efficiently to emerging viruses and other pathogens.
It may seem strange to compare threats posed by human interactions with winged mammals that sleep upside down in caves to that of a terrorist group or a nuclear-armed nation. But scientific evidence — and our collective daily experience coping with Covid-19 — tells us that pandemics may equal or surpass these dangers. It is time to significantly elevate our response to them so it is equal to the peril they present.
David M. Morens is an infectious disease physician, chair of the American Committee on Arthropod-Borne Viruses, a fellow of the American Society of Tropical Medicine and Hygiene, and senior adviser to the director of the National Institute of Allergy and Infectious Diseases. Joel G. Breman is physician-epidemiologist, senior scientist emeritus at the Fogarty International Center of the National Institutes of Health, and president of the American Society of Tropical Medicine and Hygiene. The opinions expressed here are those of the authors and do not necessarily represent the positions of their employers or affiliated organizations.
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