Spillover: Animal Infections and the Next Human Pandemic

by David Quammen

It’s a word of the future, destined for heavy use in the twenty-first century.

Approval ratings for bats are never high. Now in Australia they went lower.

they are not simply happening to us; they represent the unintended results of things we are doing. They reflect the convergence of two forms of crisis on our planet. The first crisis is ecological, the second is medical.

Will the Next Big One be caused by a virus? Will the Next Big One come out of a rainforest or a market in southern China? Will the Next Big One kill 30 or 40 million people?

Yikes!

“I’m a Hot Zone kid,” Warfield told me much later. She couldn’t vouch for the book’s scientific accuracy, she added, but its effect on her then was galvanic.

Two schools of thought have arisen. I think of them as the wave school and the particle school—my little parody of the classic wave-or-particle conundrum about the nature of light.

Such a great connection

The particle view of Ebola sees it as a relatively old and ubiquitous virus in Central African forests, and each human outbreak as an independent event, primarily explicable by an immediate cause.

The wave view suggests that Ebola has not been present throughout Central Africa for a long time—that, on the contrary, it’s a rather new virus, descended from some viral ancestor, perhaps in the Yambuku area, and come lately to other sites where it has emerged. The local outbreaks are not independent events, but connected as part of a wave phenomenon. The virus has been expanding its range within recent decades, infecting new populations of reservoir in new places. Each outbreak, by this view, represents a local event primarily explicable by a larger cause—the arrival of the wave.

Another crucial aspect of measles is that the virus is not zoonotic. If it were—if it circulated also in animals living near or among human communities—then the question of critical community size would be moot.

Alternatively, anyone who favors Intelligent Design in lieu of evolution might pause to wonder why God devoted so much of His intelligence to designing malarial parasites.

“Small increases of the infectivity rate may lead to large epidemics.” This quiet warning has echoed loudly ever since. It’s a cardinal truth, over which public health officials obsess each year during influenza season.

Raise the blood temperature of the infected person a few degrees, he realized, and you might cook the bacterium to death. So he began inoculating patients with Plasmodium vivax.

SARS got on a plane in Hong Kong and went to Toronto. Its arrival in Canada was unheralded but then, within days, it began to make itself felt. It killed the seventy-eight-year-old grandmother who had carried it into the country, killed her grown son a week later, and spread through the hospital where the son had received treatment.

Another ominous trait was that the new bug, whatever it might be, seemed so very good at riding airplanes.

Population estimates of R0 can obscure considerable individual variation in infectiousness,” according to J. O. Lloyd-Smith and several colleagues, writing in the journal Nature, “as highlighted during the global emergence of severe acute respiratory syndrome (SARS) by numerous ‘superspreading events’ in which certain individuals infected unusually large numbers of secondary cases.”

the symptoms looked a little bit too much like influenza—or, more precisely, like influenza at its worst.

Would you dine on a monkey? Without a blink he said yes, with a proviso: that the monkey meat seemed appetizing. What about ape? If you were in Africa, would you eat gorilla or chimpanzee? “I can’t draw the line there,” he answered. “It’s either eat meat, or don’t eat meat. You’d have to test me by putting human flesh in front of me.”

The rat meat was mild, subtle, faintly sweet. There were many small femurs and ribs. One eats bamboo-rat hocks with one’s fingers, I learned, sucking clean the bones and piling them politely on the table beside one’s bowl, or else dropping them on the floor (the preferred method of Mr. Wei’s father,

the most crucial, was inherent to the way SARS-CoV affects the human body: Symptoms tend to appear in a person before, rather than after, that person becomes highly infectious.

If SARS had conformed to the perverse pattern of presymptomatic infectivity, its 2003 emergence wouldn’t be a case history in good luck and effective outbreak response. It would be a much darker story.

Double yikes

“If mammals didn’t make ticks sick,” Ostfeld said, “ticks wouldn’t make mammals sick later on.”

Risk of Lyme disease seems to go up as the roster of native animals, in a given area, goes down. Why? Probably because of the differences in reservoir competence between mice and shrews (both with high competence) and almost all other vertebrate hosts (low competence) that may share habitat with them.

a zoonosis may spill over more readily within a disrupted, fragmented ecosystem than within an intact, diverse ecosystem.

If that sounds like good news, rather than a spooky enigma, you’re more of an optimist than I am.

through the mesh, managed to jab the Schwarzenegger macaque in its thigh; in the same motion, he rammed down the plunger. It was a nifty move, somewhat outside the usual duties of a family-practice physician from Seattle.

A sneeze travels downwind, more or less at random, but a mosquito can fly upwind toward a victim. That’s what makes vectors such effective modes of transmission.

If Nipah virus hadn’t been zoonotic, capable of leaping into humans and killing them, Field told me, it might have passed as no more than “a blip on the productivity output” of Malaysian pig

It’s almost impossible to screen your pigs, cows, chickens, ducks, sheep, and goats for a virus of any sort until you’ve identified that virus (or at least a close relative), and we have only begun trying.

The ducks and chickens turned out to be a false lead. See how tricky it is to do epidemiology in a Bangladesh village? None of those innocent childhood pastimes I’ve mentioned, from duck burial to cricket, was significantly more associated with the infected boys

Occasionally dead bats are found floating in the pots.” But that’s not enough to eliminate the demand for raw sap.

Remember measles, circulating endemically in cities of five hundred thousand people or more? Bats probably meet the critical community size standard more consistently than most other mammals.

detect antibodies against Marburg (in thirteen of the roughly six hundred fruit bats sampled) and fragments of Marburg RNA (in thirty-one of the bats), but they also did something more difficult and compelling. Antibodies and RNA fragments, though significant, were just the same sorts of secondary evidence that had provisionally linked the Ebola virus to bats. This team had gone a step farther: They’d found live virus.

“It confirmed my suspicions that these bats are moving,” Amman said—and moving not only through the forest but from one roosting site to another. Travel of individual bats (such as K-31) between far-flung roosts (such as Kitaka and Python) implied circumstances whereby Marburg virus might ultimately be transmitted all across Africa, from one bat encampment to another. It suggested opportunities for infecting or reinfecting bat populations in sequence, like a string of blinking Christmas lights. It voided the comforting assumption that this virus is strictly localized.

It’s no condescension against Bakwele culture to note that butchering chimpanzees to eat their arms, as part of an ancient and bloody ritual, could be a very good way to acquire SIVcpz

Throughout the rest of the world you see AIDS-education materials crying out: Practice safe sex! Wear a condom! Don’t reuse needles! Here the message was: Don’t eat apes!

French Equatorial Africa then known as Oubangui-Chari) during 1917–1919, treated 5,347 trypanosomiasis cases using only six syringes.

“The duck is the Trojan horse,” Webster told me. That’s where the danger lurked secretly, he meant. Wild ducks might land on your flooded paddy, carrying the virus, fouling the water, and infecting your domestic ducks. Your ducks would appear fine, but when your son brought them home to their coop for the night, they could infect your chickens. Before long your chickens—and your son too—might be dead of bird flu.

Global Viral Forecasting Initiative (GVFI), financed in part by Google and created by a bright, enterprising scientist named Nathan Wolfe, one of whose mentors was Don Burke. GVFI gathers blood samples on small patches of filter paper from bushmeat hunters and other people across tropical Africa and Asia,