Technological advancements effectively combat future disease.

“You’ll tell us when you’re worried, right?”∂ That was the question posed to me countless times at the height of the∂ 2014 West African Ebola outbreak. As an infectious disease physician,∂ I was interviewed on outlets such as CNN, NPR, and Fox News about the∂ dangers of the virus, and the answer I gave was always the same:∂ “Ebola is a deadly, scary disease, but it is not that contagious. It∂ will not find the U.S. or other industrialized nations hospitable.”∂ In other words, no, I wasn’t worried—and not because I have a rosy∂ outlook on infectious diseases. I’m well-aware of the damage these∂ diseases are causing around the world: HIV, malaria, tuberculosis; the∂ influenza pandemic that took the world by surprise in 2009; the∂ anti-vaccine movement bumping cases of measles to an all-time∂ post-vaccine-era high; antibiotic-resistant bacteria threatening to∂ collapse the entire structure of modern medicine—all these, like∂ Ebola, are continuously placing an enormous number of lives at risk.∂ But when people ask me if I’m worried about infectious diseases,∂ they’re often not asking about the threat to human lives; they’re∂ asking about the threat to human life. With each outbreak of a∂ headline-grabbing emerging infectious disease comes a fear of∂ extinction itself. The fear envisions a large proportion of humans∂ succumbing to infection, leaving no survivors or so few that the∂ species can’t be sustained.∂ I’m not afraid of this apocalyptic scenario, but I do understand the∂ impulse. Worry about the end is a quintessentially human trait.∂ Thankfully, so is our resilience.∂ For most of mankind’s history, infectious diseases were the∂ existential threat to humanity—and for good reason. They were quite∂ successful at killing people: The 6th century’s Plague of Justinian∂ knocked out an estimated 17 percent of the world’s population; the∂ 14th century Black Death decimated a third of Europe; the 1918∂ influenza pandemic killed 5 percent of the world; malaria is estimated∂ to have killed half of all humans who have ever lived.∂ Any yet, of course, humanity continued to flourish. Our species’∂ recent explosion in lifespan is almost exclusively the result of the∂ control of infectious diseases through sanitation, vaccination, and∂ antimicrobial therapies. Only in the modern era, in which many∂ infectious diseases have been tamed in the industrial world, do people∂ have the luxury of death from cancer, heart disease, or stroke in the∂ 8th decade of life. Childhoods are free from watching siblings and∂ friends die from outbreaks of typhoid, scarlet fever, smallpox,∂ measles, and the like.∂ So what would it take for a disease to wipe out humanity now?∂ In Michael Crichton’s _The Andromeda Strain_, the canonical book in∂ the disease-outbreak genre, an alien microbe threatens the human race∂ with extinction, and humanity’s best minds are marshaled to combat∂ the enemy organism. Fortunately, outside of fiction, there’s no∂ reason to expect alien pathogens to wage war on the human race any∂ time soon, and my analysis suggests that any real-life domestic∂ microbe reaching an extinction level of threat probably is just as∂ unlikely.∂ When humans began to focus their minds on the problems posed by∂ infectious disease, human life ceased being nasty, brutish, and short.∂ Any apocalyptic pathogen would need to possess a very special∂ combination of two attributes. First, it would have to be so∂ unfamiliar that no existing therapy or vaccine could be applied to it.∂ Second, it would need to have a high and surreptitious∂ transmissibility before symptoms occur. The first is essential because∂ any microbe from a known class of pathogens would, by definition, have∂ family members that could serve as models for containment and∂ countermeasures. The second would allow the hypothetical disease to∂ spread without being detected by even the most astute clinicians.∂ The three infectious diseases most likely to be considered∂ extinction-level threats in the world today—influenza, HIV, and∂ Ebola—don’t meet these two requirements. Influenza, for instance,∂ despite its well-established ability to kill on a large scale, its∂ contagiousness, and its unrivaled ability to shift and drift away from∂ our vaccines, is still what I would call a “known unknown.” While∂ there are many mysteries about how new flu strains emerge, from at∂ least the time of Hippocrates, humans have been attuned to its risk.∂ And in the modern era, a full-fledged industry of influenza∂ preparedness exists, with effective vaccine strategies and antiviral∂ therapies.∂ HIV, which has killed 39 million people over several decades, is∂ similarly limited due to several factors. Most importantly, HIV’s∂ dependency on blood and body fluid for transmission (similar to Ebola)∂ requires intimate human-to-human contact, which limits contagion.∂ Highly potent antiviral therapy allows most people to live normally∂ with the disease, and a substantial group of the population has∂ genetic mutations that render them impervious to infection in the∂ first place. Lastly, simple prevention strategies such as needle∂ exchange for injection drug users and barrier contraceptives—when∂ available—can curtail transmission risk.∂ Ebola, for many of the same reasons as HIV as well as several others,∂ also falls short of the mark. This is especially due to the fact that∂ it spreads almost exclusively through people with easily recognizable∂ symptoms, plus the taming of its once unfathomable 90 percent∂ mortality rate by simple supportive care.∂ Beyond those three, every other known disease falls short of what∂ seems required to wipe out humans—which is, of course, why we’re∂ still here. And it’s not that diseases are ineffective. On the∂ contrary, diseases’ failure to knock us out is a testament to just∂ how resilient humans are. Part of our evolutionary heritage is our∂ immune system, one of the most complex on the planet, even without the∂ benefit of vaccines or the helping hand of antimicrobial drugs. This∂ system, when viewed at a species level, can adapt to almost any enemy∂ imaginable. Coupled to genetic variations amongst humans—which open∂ up the possibility for a range of advantages, from imperviousness to∂ infection to a tendency for mild symptoms—this adaptability ensures∂ that almost any infectious disease onslaught will leave a large∂ proportion of the population alive to rebuild, in contrast to the∂ fictional Hollywood versions.∂ While the immune system’s role can never be understated, an even∂ more powerful protector is the faculty of consciousness. Humans are∂ not the most prolific, quickly evolving, or strongest organisms on the∂ planet, but as Aristotle identified, humans are the rational∂ animals—and it is this fundamental distinguishing characteristic∂ that allows humans to form abstractions, think in principles, and plan∂ long-range. These capacities, in turn, allow humans to modify, alter,∂ and improve themselves and their environments. Consciousness equips∂ us, at an individual and a species level, to make nature safe for the∂ species through such technological marvels as antibiotics, antivirals,∂ vaccines, and sanitation. When humans began to focus their minds on∂ the problems posed by infectious disease, human life ceased being∂ nasty, brutish, and short. In many ways, human consciousness became∂ infectious diseases’ worthiest adversary.