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30 september 2016
Spillover is the kind of nonfiction book I frequently disdain here: I used to call them "voice-driven," which it is, but a better term is "interview-driven." You know the type, the author as character hears about something interesting in Borneo and next day, she's rattling down a road in Borneo on a bus. But I forgive Spillover its sometimes hilarious technique (seriously, where's the money to go on these impulsive jaunts come from?) because David Quammen has such an engaging voice. And no matter where he goes and who he interviews, his interests lie in exposition for the reader's benefit, not in local color or character sketching.
Quammen must have logged a billion frequent-flyer miles in search of the sites where zoonotic diseases did what zoonotic diseases do: "spill over" from host populations of animals into human communities. At one point he reflects on the oddness and possible triviality of his quest. At several points he reflects on its riskiness, even foolhardiness. Why is it interesting to him? Because so many great pandemics have reached humans via animal hosts: the plague, the great influenza, HIV/AIDS. And the "Next Big One" is likely to arrive the same way.
How humans learned the workings of these diseases is a great detective story. Many of the central figures are still living, and most did their key work within living memory. Our knowledge was of course still limited even as of 2012 when Quammen wrote, and in a sense will always be, because pathogens evolve too quickly for us to know definitively. But to think of 150 years ago, when the very cause of most diseases was a mystery, and compare that to our elaborate knowledge of bacteria and viruses, and the population ecology of these little germs, is to stand in wonder at the cleverness – and even more, the sheer effort – of generations of medical researchers.
Zoonoses require host populations that they can't readily kill. Contrary to popular belief, Quammen notes, viruses don't evolve toward symbiosis with the species they infect. Viruses could care less about symbiosis. Killing at a slow rate, giving host animals plenty of time to infect other hosts, is actually the "ideal" strategy. The problem for doctors is to identify the hosts of given disease organisms. At the time Quammen was writing, for instance, bats were only suspected as the hosts of Ebola, a connection now more firmly established. (Quammen also wrote before the first cases of Ebola in the U.S. were diagnosed in 2014.) Host populations can be difficult to pinpoint because the animals themselves either don't get sick, or aren't observable enough to know whether they're getting sick of a particular illness or not. Bats are hosts for many an infection, but doing veterinary checkups on wild bats is something between perilous and impossible.
Quammen recounts some fairly death-defying feats carried out by dogged researchers: capturing bats, tranquilizing monkeys, squeezing into dodgy caves, even roaming through open-air markets filled with exotic meats, which is one of the suspected gateways in many an outbreak. Mostly academics, his unsung heroes range from mathematical theoreticians to practical veterinarians. (Any prejudice you held toward veterinary medicine as somehow a poor intellectual cousin of human medicine will be dispelled by Spillover.)
Quammen writes with great energy and spirited, if sometimes gallows, humor, about diseases ranging from Hendra and psittacosis to Ebola, HIV, and SARS. He is not alarmist. For all the book's sensational qualities, Spillover is ultimately rather matter-of-fact. Humans are themselves an outbreak upon the planet, clinically speaking, and outbreaks are kept in check by counter-outbreaks. No wait, that sounds more posthumanist than Quammen might like. He simply points out that we are enmeshed in relationships with animal species (and bacterial and viral species) that earlier medical thought tried to ignore. Zoonotic diseases, for instance, cannot be eradicated unless you eradicate entire host species as well. This has worked for any potential dodo flus, and might be acceptable in the case of malaria mosquitoes. But would you want to kill off entire species of monkeys to eradicate even as scary an illness as Herpes B? And what if you were wrong, and the disease broke out again anyway? Ethics is as important as logic to Quammen's argument, which is thought-provoking – and in its vision of a planet where everything and everybody are linked to one another, oddly comforting.
Quammen, David. Spillover: Animal infections and the next human pandemic. New York: Norton, 2012. RA 639 .Q83