Spillover: the powerful, prescient book that predicted the Covid-19 coronavirus pandemic.

by David Quammen

Influenza is caused by three types of viruses, of which the most worrisome and widespread is influenza A. Viruses of that type all share certain genetic traits: a single-stranded RNA genome, which is partitioned into eight segments, which serve as templates for eleven different proteins. In other words, they have eight discrete stretches of RNA coding, linked together like eight railroad cars, with eleven different deliverable cargoes. The eleven deliverables are the molecules that comprise the structure and functional machinery of the virus. They are what the genes make. Two of those molecules become spiky protuberances from the outer surface of the viral envelope: hemagglutinin and neuraminidase. Those two, recognizable by an immune system, and crucial for penetrating and exiting cells of a host, give the various subtypes of influenza A their definitive labels: H5N1, H1N1, and so on. The term “H5N1” indicates a virus featuring subtype 5 of the hemagglutinin protein combined with subtype 1 of the neuraminidase protein. Sixteen different kinds of hemagglutinin, plus nine kinds of neuraminidase, have been detected in the natural world. Hemagglutinin is the key that unlocks a cell membrane so that the virus can get in, and neuraminidase is the key for getting back out. Okay so far? Having absorbed this simple paragraph, you understand more about influenza than 99.9 percent of the people on Earth. Pat yourself on the back and get a flu shot in November.

Influenza 101

The practical alternative to soothsaying, as Burke put it, is “improving the scientific basis to improve readiness.” By “the scientific basis” he meant the understanding of which virus groups to watch, the field capabilities to detect spillovers in remote places before they become regional outbreaks, the organizational capacities to control outbreaks before they become pandemics, plus the laboratory tools and skills to recognize known viruses speedily, to characterize new viruses almost as fast, and to create vaccines and therapies without much delay. If we can’t predict a forthcoming influenza pandemic or any other newly emergent virus, we can at least be vigilant; we can be well-prepared and quick to respond; we can be ingenious and scientifically sophisticated in the forms of our response.

How to nip pandemics in the bud

We should appreciate that these recent outbreaks of new zoonotic diseases, as well as the recurrence and spread of old ones, are part of a larger pattern, and that humanity is responsible for generating that pattern. We should recognize that they reflect things that we’re doing, not just things that are happening to us. We should understand that, although some of the human-caused factors may seem virtually inexorable, others are within our control.

That’s the salubrious thing about zoonotic diseases: They remind us, as St. Francis did, that we humans are inseparable from the natural world. In fact, there is no “natural world,” it’s a bad and artificial phrase. There is only the world. Humankind is part of that world, as are the ebolaviruses, as are the influenzas and the HIVs, as are Nipah and Hendra and SARS, as are chimpanzees and bats and palm civets and bar-headed geese, as is the next murderous virus—the one we haven’t yet detected.

The mathematical ecologist’s term for variousness of behavior is “heterogeneity,” and Dwyer’s models have shown that heterogeneity of behavior, even among forest insects, let alone among humans, can be very important in damping the spread of infectious disease. “If you hold mean transmission rate constant,” he told me, “just adding heterogeneity by itself will tend to reduce the overall infection rate.” That sounds dry. What it means is that individual effort, individual discernment, individual choice can have huge effects in averting the catastrophes that might otherwise sweep through a herd. An individual gypsy moth may inherit a slightly superior ability to avoid smears of NPV as it grazes on a leaf. An individual human may choose not to drink the palm sap, not to eat the chimpanzee, not to pen the pig beneath mango trees, not to clear the horse’s windpipe with his bare hand, not to have unprotected sex with the prostitute, not to share the needle in a shooting gallery, not to cough without covering her mouth, not to board a plane while feeling ill, or not to coop his chickens along with his ducks. “Any tiny little thing that people do,” Dwyer said, if it makes them different from one another, from the idealized standard of herd behavior, “is going to reduce infection rates.” This was after I had asked him to consider The Analogy and he had pushed his brain against it for half an hour.

The power YOU possess