When it emerged in the United Kingdom during the late 1980s, mad cow disease seemed a gruesome anomaly. Cattle got sick and then so did people. The human victims suffered dementia, memory loss, personality change, clumsiness, and other forms of degenerative impairment, all leading to death. Their misfortune was traceable to eating beef from certain cows, animals that had been fed on a diet contaminated with . . . something nefarious. The nefarious thing was eventually identified as a prion, a protein molecule that had become folded and dysfunctional in a way contagious to similar proteins, especially within brain matter. Slowly, as the ailment progressed in a victim over months and years, more and more molecules folded, like a mousetrap cascade—flappity flap flap—and the person’s brain became riddled with little holes. This seemed fantastic.
We can now see that it was neither fantasy nor anomaly. It was part of a pattern. The pattern is that strange pathogens are emerging from nonhuman animals to cause terrible diseases in people. The human version of mad cow, known as variant Creutzfeldt-Jakob, is just one of them.
We are part of the natural world
The fancy name for such a disease is zoonosis. That simply means: an animal infection transmissible to humans. More than half of all our infectious diseases fall within this category, and the list includes not only some old, notorious killers (bubonic plague, yellow fever, influenza) but also many scary new scourges that have emerged more recently. Ebola is a zoonosis. So are West Nile fever, SARS, Lyme disease, AIDS, hantavirus pulmonary syndrome, and a long list of others. Most of them share two characteristics that set them apart from mad cow. They come to us from wildlife, not from our livestock. And they are caused not by prions, but by viruses.
These new diseases accomplish, in their grim ways, what St. Francis of Assissi tried to do rather more gently. They remind us of our connectedness with the natural world. They remind us, in fact, that there is no “natural world” in distinction from our world. There is only the world, and we are part of it. So are rats and monkeys and birds and bats and mosquitoes and viruses. Infectious diseases—particularly those caused by pathogens that pass between one species and another—are just another form of intimate relationship that binds us within the pageant of life on Earth.
The most notable point about zoonoses these days is that the phenomenon seems to be getting worse. Within the past six decades, there’s been a long, ugly litany of new names, new diseases, new viruses passing into humans from wildlife. Some are infamous and some more obscure: Kyasanur Forest disease (1957), Machupo (1961), Marburg (1967), Lassa (1969), Ebola (1976), HIV-1 (first noticed in 1981, identified in 1983), HIV-2 (1986), hantavirus in the U.S. (1993), Hendra in Australia (1994), avian influenza (1997), Nipah encephalitis (1998), SARS (2003), and many more. The worst of such viruses are especially problematic because they live inconspicuously in their natural animal hosts (a rodent? a bat? a monkey?) and then, once they’ve spilled over into humans, they replicate quickly, they mutate, they evolve, they adapt, they spread, and they kill.
Some of them spread quite well; some of them kill quite efficiently. The very worst do both. The 1918-19 influenza claimed about 50 million victims. AIDS has caused 30 million deaths so far, and we’re not done with it. A severe new strain of influenza, spilling over from a wild duck in Guangdong, or from a shearwater in Queensland, could also prove fatal to millions of people.
And nowadays, in our globalized world, new infections travel farther and faster than ever before. The SARS virus traveled out of southern China to Hong Kong by bus, in the body of one man, who fell ill and started coughing; then it wafted through the corridors of a hotel where he stayed. From the hotel, having passed into other victims, it traveled onward to Beijing and Toronto and Singapore and Hanoi in a matter of hours. The same virus could just as easily—but for happenstance—have disembarked in New York or Paris or Berlin. It was lethal to about one person in ten among those it infected and might have caused many more deaths, if it hadn’t been so promptly identified and so efficiently contained.
When disease experts suffer insomnia, these are among the dark possibilities on which they ruminate. They wonder when the Next Big One will emerge. They wonder which kind of virus it will be, spilling over from what animal, in what remote corner of the planet. They wonder whether human intelligence—in the form of epidemiology, disease ecology, medical innovation, public health planning, and an informed citizenry—will be adequate to the challenge presented by some new bug. We should wonder the same.
No need for nightmares
Taking seriously this prospect of a forthcoming pandemic, though, is very different from saying that some nightmarish new virus may wipe out humanity altogether. The disease experts are not saying that. At its most horrific, which would be quite horrific enough, such a catastrophe of infection could well claim tens of millions of lives—as the 1918 influenza did, and as AIDS has more recently done. But the facts of population biology, genetic variation, Darwinian evolution, and human abundance and adaptability insure that any pandemic, however severe, will leave many human survivors. To fret about “the end of humanity” from some such cause is to miss the point and to distort the disease conversation away from its sober realities.
There’s no need to lie awake worrying, and there’s no basis for eschatological gloom. By light of day we should inform ourselves about the true scope of the problem, the dynamics of such spillovers, and what can done. “Zoonosis” may sound like a technical term, but it’s destined to be vernacular in the 21st century.