The Coming Plague (99 page)

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Authors: Laurie Garrett

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The deer carried the ticks with them as they made long foraging journeys through woodlands and into suburban yards. Because there were no predators around to keep the deer population in check, their sheer numbers were great enough to force the animals to scour boldly for food, often stepping right into suburban front yards and patios to nibble at carefully cultivated azaleas and lawns. That, in turn, guaranteed that three more species—
Homo sapiens
, felines, and canines—would come in contact with
I. dammini
ticks and the
B. burgdorferi
bacteria they carried.
16
Studies in New York showed that the territory inhabited by the
I
.
dammini
tick was expanding at a steady and rapid rate, as deer, pet dogs, humans, rodents, and even some birds carried the insects further and further from the initial outbreak sites. By 1991, Lyme, the disease, and
I. dammini,
its vector, had spread widely throughout wooded and scrub-brush ecospheres all over the Northeast. Their invasion, and the epidemic they spawned, was new.
17
To understand how, and why, Lyme disease had suddenly emerged in North America, Spielman and his colleagues tried to recapitulate the history of the expansion of
I. dammini's
territory.
18
The work took Spielman's group back in time to the arrival of British colonists in North America. When the Pilgrims landed in Massachusetts they set to work with Puritanical fervor clearing local forests and building settlements, Spielman said. By the late eighteenth century Massachusetts was the center of North America's iron industry, and remaining forests of the region were denuded to supply fuel for iron smelting. By the nineteenth century most of the woodlands of the entire Northeast had been so thoroughly
devastated that housing construction required importation of wood from what were then the western territories.
“The result was an ecology just as artificial as a concrete parking lot,” Spielman said, speaking of the later return of flora and fauna to the denuded areas. The grand tall trees, oaks and larches, never returned, nor did the large carnivorous animals. What did replace the old forests was an ecology similar to what probably had comprised the edges of the woods in the sixteenth century: scrub brush, small birches and other nonshade trees, meadows, deer, chipmunks, voles, squirrels, and birds.
“It's an artificial landscape that we have created, largely by neglect, here in the East,” Spielman said, adding that the new ecology was filled with insect and rodent vectors, “lurking out there in this system of change.”
Into the denuded forests came aggressor flora and, unchallenged by predators, the deer, rodents, and
I. dammini
ticks. As their numbers soared, bringing the deer, in particular, back from the edge of extinction in the Northeast, a new disease paradigm emerged.
19
As the invasion of
I. dammini
ticks and deer into artificially reforested areas demonstrated, no matter how hard
Homo sapiens
struggled to pave the world, Nature never ceased trying to force its way back. No area could escape the steady global spread of plant, animal, and insect species. In the absence of natural predators or competitors, alien species introduced into artificial ecologies—including mega-cities—could quickly overwhelm all suitable niches. And with the immigrant species could—and had—come microbes that were new to the local environment.
The Lyme case demonstrated the fallacy of viewing flora and fauna per se as “natural.” From the point of view of microbial opportunity, loss of original biodiversity couldn't be corrected merely by introducing a handful of aggressor species.
 
During the early 1980s ecologists Paul and Anne Ehrlich of Stanford University developed the “Rivet Hypothesis” of diversity. They thought of the ecosphere as a huge airplane held together by steel rivets, or species. As each species died out, the total mass of the “airplane” might remain the same, but rivets were lost, weakening the overall structure. Eventually, a critical number of rivets having been lost, the plane would come apart, crash, and perish.
The epochal “Rivet Hypothesis” was given credibility by several experiments conducted in laboratories around the world. Scientists grew plants in environmentally sealed greenhouses filled with devices that measured carbon dioxide, oxygen, and total biomass. And it turned out that the more diverse the species assortment in a greenhouse—even when total biomass, sunlight, and all other factors were equal—the greater the oxygen production and general vitality of the little ecosphere.
In a survey of nineteen tropical forest ecospheres, researchers from the Missouri Botanical Garden found striking evidence that the changing ratio
of oxygen to carbon dioxide was already having dire effects: forest turnover rates were increasing dramatically. Whole sections of forest biota “rivets” were dying and regenerating with radically escalating haste. In several major forests—particularly in Central Africa and Amazonia—turnover rates over the 1970–94 period had increased 150 percent every five years. The result, wrote Al Gentry (who died in a plane crash over Ecuador while making these surveys), was a net decrease in biodiversity as the older, massive hardwood trees, and the multitude of flora and fauna that existed in the ecospheres they created, died off and were replaced by a limited range of aggressive smaller trees and tropical vines. These gas-dependent species had less dense wood, and could transform forests into carbon sinks which would emit chemicals that further exacerbated the CO
2
imbalance and ozone crisis. Gentry predicted an accelerated rate of species extinctions and a radical change in the density and diversity of the world's rain forests, all occurring at astonishing speed.
20
From an atmospheric scientist's point of view the most crucial issue was the decline in oxygen production from the earth's flora due both to its overall declining mass and to the lowered range of diversity among surviving vegetation. Coupled with increased production of carbon dioxide owing primarily to human fossil fuel consumption and forest burning, and the expected increase in oxygen-dependent
Homo sapiens
, a clear chemical crisis loomed.
The most immediate impact was chemical destruction of the earth's ozone layer. The invisible layer of gas composed primarily of uncoupled oxygen atoms, or ozone, had unique physical properties. The atoms responded to specific wavelengths of light, repelling those in the ultraviolet and infrared bands. Little light in those wavelengths emanated upward from the earth's surface, but the planet was bombarded with such radiation from the sun. If not for the ozone layer, the planet would be a humanly uninhabitable hothouse bathed in mutation-causing ultraviolet light.
Throughout the 1980s researchers, particularly at NASA's Goddard Space Flight Center, amassed evidence that the ozone layer was weakening, especially over the South Pole. Over Antarctica an actual seasonal hole had developed in the ozone layer, through which poured levels of ultraviolet light unprecedented in known human history.
By 1990 a fierce debate raged in scientific circles over the size and significance of that ozone hole. But something was undoubtedly happening to the global ecology. Glaciers were retreating in some parts of the world, skin cancer rates were up in Australia and southern Chile, surface temperatures of oceans in some areas had risen, and mean surface air temperatures were up. Some researchers found, in fossils and deep glacial ore samples, evidence of such periods of warming in the earth's past, indicating that such events could all be part of a historic cycle on the planet. Further, it was possible that the bulk of the warming was induced not by human pollution and rain forest destruction, but by natural catastrophic events
such as the 1991 eruption of the Mount Pinatubo volcano in the Philippines.
21
There was strong evidence, however, that halogen ions, particularly chlorides and bromides, were making their way via human pollution into the atmosphere. These were the breakdown products of thousands of plastics, pesticides, fuels, detergents, and other modern materials. Once inside the ozone layer, the halogens acted as chemical scavengers, attaching themselves to free oxygen atoms to form heavy molecules that then fell out of the protective layer into lower tiers of the earth's atmosphere. In this way, ozone was actively depleted.
Most Western scientists insisted that the pollution- and deforestation-driven ozone depletion and global warming hypothesis was correct, though among believers there were significant differences of opinion about its current and forecast severities. The strongest evidence supported an estimate of a net global temperature increase of half a degree centigrade during the twentieth century, with five degrees centigrade marking the difference between, on the one hand, the Ice Age and, on the other, a severely deleterious greenhouse warming effect.
The first outcome of this warming was a higher surface water evaporation rate, which, in turn, led to greater levels of rainfall and monsoon in key areas of the planet. In places that normally had low levels of rainfall, such as the Sahara Desert, there would be even less precipitation. The net result would be greater extremes in water distribution, with severe droughts afflicting some parts of the planet, flooding and hurricanes hitting others. That, in turn, was expected to alter everything from the migrations of birds to the feeding patterns of blue whales; from habitat ranges of malarial mosquitoes to the amount of the planet's arable land suitable for profitable agricultural growth.
22
The lesson of macroecology was that no species, stream, air space, or bit of soil was insignificant; all life forms and chemical systems on earth were intertwined in complex, often invisible ways. The loss of any “rivet”—even a seemingly obscure one—might imperil the physical integrity of the entire “plane.”
The “plane,” in the Ehrlichs' scenario, was destined to crash. What hadn't been anticipated was that the plane would first get sick, heavily encumbered by emerging pathogenic microbes.
In 1987, Siberian fishermen and hunters working around Lake Baikal noticed large numbers of dead seals (
Phoca sibirica
) washing up along the shores of the huge Central Asian lake. By year's end, the seal death toll would top 20,000, or nearly 70 percent of the entire population. The world's deepest lake—a mile deep—was a unique 12,000-square-mile ecosphere inhabited by a number of species of flora and fauna found nowhere else in the world, including the dark gray freshwater seals. Because the Soviet government had long used the country's lakes as waste dumps, it was first assumed that the seals were victims of some toxic chemicals.
But with the spring thaw of 1988 came an apparent epidemic of miscarriages among female harbor seals (
P. vitulina
) in the North Sea along the coasts of Sweden and Denmark. Some 100 spontaneously aborted seal pups were recovered, a few of which survived long enough for scientists to study their symptoms: lethargy, breathing difficulties, nasal congestion.
23
A quick-and-dirty analysis of the pups' blood revealed that the dying and dead seals had antibodies that reacted weakly in laboratory tests against canine distemper viruses.
With the arrival of summer 1988 came hundreds of dead adult seals in the North Sea area. They washed up upon shores separated by huge expanses of land and sea, from the western Baltic Sea area of Sweden and Denmark to the far west coast of Scotland. By August dead seals were even found scattered along the beaches of northern Ireland.
In laboratories in the Netherlands, Ireland, Russia, and the United States, scientists swiftly determined that the seals were dying from a morbillivirus—the same class that included human measles, cattle rinderpest virus, and canine distemper. The die-offs continued well into 1990, eventually claiming more than 17,000 North Sea harbor seals, or more than 60 percent of the entire population.
Scientists working in laboratories from Atlanta to Irkutsk swiftly determined that two different viruses were responsible for what seemed to be separate seal epidemics in Lake Baikal and the North Sea. The virus isolated from the massively infected lungs of Lake Baikal's seals was dubbed phocine distemper virus-2 (PDV-2), and it proved virtually identical to canine distemper virus.
The North Sea seals, however, were suffering from something never before seen. Their microbial assailant, named phocine distemper virus-1 (PDV-1), was distinct from any other known morbillivirus. It appeared to be something new, and the extraordinary death rates among harbor seals indicated that their immune systems had never previously encountered such a virus.
While the seal experts worked on that puzzle, veterinarians in Spain were examining dolphins that were beaching themselves along the Mediterranean coast of Catalonia, Spain. By July 1990 more than 400 Mediterranean dolphins had washed onto the shores of North Africa, Spain, and France, clearly suffering respiratory distress. Autopsies of the animals revealed startling brain damage and acute immunodeficiencies. Similar signs of immune deficiency had already been documented in the North Sea seals, and accounts in the popular Spanish press were soon calling the mysterious marine mammal ailment “dolphin AIDS.”

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