Penguin walking logo
EPILOGUE
The Pandemic Century
“Gentlemen, it’s the microbes that will have the last word.”
Louis Pasteur
Sharks never attack swimmers in the North Atlantic. Flu is a bacterial disease and a threat to infants and the elderly, not young adults in the prime of life. Ebola is a virus endemic to forested regions of equatorial Africa—it can’t reach a major city in West Africa, let alone one in North America or Europe. Coronaviruses are uninteresting—the “Cinderellas” of the viral world; they might present a threat in hospitals and other closed environments, such as cruise ships, but they are unlikely to cause a global pandemic.
As the pandemic century that began in 1918 ends, we know better than to trust the pronouncements of experts. Battered by their repeated failure to predict deadly outbreaks of infectious disease, even the experts have come to recognize the limits of medical prognostication. This is not only because microbes are highly mutable—that has been known since Pasteur’s time—but because we are continually lending them a helping hand. Time and again, we assist microbes to occupy new ecological niches and spread to new places in ways that usually only become apparent after the event. To judge by the recent run of pandemics and epidemics, the process seems to be speeding up. If HIV and SARS were wake-up calls, then Ebola, Zika, and Covid-19 confirmed it. “Despite extraordinary advances in medical science, we cannot be complacent about the threat of infectious diseases,” acknowledged the National Academy of Medicine in an influential report published in 2016. “The underlying rate of emergence of infectious diseases appears to be increasing.”1
Why this should be the case—if it is the case—is a matter of ongoing research and conjecture. Certainly urbanization and globalization would appear to be key factors. By concentrating large numbers of people in cramped and often unsanitary spaces, the mega-cities of Asia, Africa, and South America, like Athens in the time of Thucydides, provide ideal conditions for the amplification and spread of novel pathogens. Sometimes technology and alterations of the built environment can mitigate the risks that such overcrowding presents for the transfer of pathogens to people. The plague abatement measures in the Mexican quarter of Los Angeles in 1924 may have been brutal and morally questionable (certainly, it is hard to imagine environmentalists and community activists in California tolerating the wholesale demolition of minority neighbourhoods and the mass slaughter of squirrels today), but at the time they were effective in removing the threat of plague from downtown LA and its harbour. Likewise, air conditioners and modern cooling systems are very effective ways of insulating people from the mosquitoes that breed in and around urban high rises and favelas, but as the Legionnaires’ disease outbreak demonstrated, and SARS confirmed, water towers and fanned air can also present new disease risks, particularly in closed environments such as hotels and hospitals.
Greater global interconnectivity driven by international travel and commerce is undoubtedly another key factor. While in the sixteenth century it took several weeks for smallpox, measles, and other Old World pathogens to reach the New World, and even longer for the vectors of diseases like yellow fever to become established in the Americas. Today, international jet travel means that an emerging virus can land in any country or continent on the globe within seventy-two hours. It is not the microbes that are doing this, but our own technology. Wuhan, for instance, is a key domestic and international hub with over one hundred direct flights to more than seventy countries worldwide. Prior to the lockdown, any number of individuals—business people, tourists, foreign language tutors—could have transported the virus beyond China’s borders by the simple expedient of boarding a plane. Indeed, tens of millions of us annually make such trips in aircraft for either business or pleasure, and as flights become cheaper and passengers make more and more journeys, the risks are only likely to grow. Herded into airline waiting rooms, then crammed into economy row seats, we resemble nothing more than the captive Amazonian parakeets who introduced psittacosis to Baltimore and other US cities in 1929. The difference is that the parakeets had no choice about their accommodation, whereas we do. As Alfred Crosby put it, international jet travel is like “sitting in the waiting room of an enormous clinic, elbow to elbow with the sick of the world.”2 Yet budget airlines continue to grow in popularity.
Another increasingly important factor is how the growing demand for milk and animal proteins in rapidly industrializing countries, such as China, is putting pressure on previously remote animal habitats where pathogens like coronavirus reside. As an example, for more than three centuries Guangdong, the epicentre of the 2002 SARS outbreak, practised a subsidence farming model, whereby rice-farmers would raise pigs, chickens, and ducks on plots of land adjacent to rice paddies. These backyard farms were ecologically sustainable and provided all the food requirements for farmers and their families. They also produced surpluses that could be sold at market for cash, supplementing farmers’ meagre incomes. But with the advent of the Livestock Revolution in the 1980s and the arrival of so-called industrial food production conglomerates this began to change. Heavily capitalized broiler companies began to undercut traditional subsistence farmers, forcing smallholders to look for new sources of protein and income. Many of them turned to farming “wild” animals, such as civet cats and pangolins. As the market for these traditional Chinese delicacies grew and they were rebranded as luxury products, wild animals started to command premium prices at “wet” markets. As the anthropologists Christos Lynteris and Lyle Fearnley explain, one of the advantages of this style of farming is that smallholders are able to transport animals to market without the involvement of large-scale food processing firms and supermarkets.3 At the same time, however, state-backed enterprises and industrial farms have gobbled up more and more cultivable land, forcing smallholders to look to “uncultivated” plots closer to the edge of rainforests. These areas, of course, are the same zones inhabited by bat populations, a factor that makes the spillover of novel viruses to farmed animals and humans much more likely.
Anthropologists and sociologists, such as Mike Davis, have been warning about the unintended ecological consequences of the Livestock Revolution for years.4 Unsurprisingly, so have disease ecologists such as Peter Daszak. Indeed, in 2017 Daszak and his colleagues in the EcoHealth Alliance compared information about emerging infectious diseases “hotspots” with demographic and environmental data, such as climate change and shifts in population density and land-use patterns. They concluded that the risk of disease emergence was “elevated in tropical forest regions, high in mammal biodiversity, and experiencing anthropogenic land use changes related to agricultural practices”.5 In other words, permitting people to farm on the edge of forests that are home to a diverse range of mammalian species, or to penetrate deeper into the same forests in search of timber and bushmeat, presents clear risks for pandemic emergence events.
These insights are valuable, not least because they underline the way in which infectious disease is part of an ecological web that is itself influenced by a constellation of shifting economic, social, and environmental factors. Or, as the Rockefeller researcher René Dubos observed in 1958, “microbial disease is one of the inevitable consequences of life in a world where nothing is stable.”6 That is why Dubos recommended that in a world of rapid environmental, ecological and social change it was incumbent on scientists, to “avoid pride of intellect and guard against any illusion or pretense as to the extent and depth of what he knows”. Instead, Dubos advised medical researchers to “develop an alertness to the unexpected, an awareness of the fact that many surprising effects are likely to result from even trivial disturbances of ecological equilibrium”.7
Dubos was not the only thinker to reject a narrow “germ-eye” view of our interactions with microbes. The social historian of medicine Charles Rosenberg, in an influential essay published in the wake of the AIDS pandemic, also advised against treating germs merely as contagions that needed to be eradicated. Prior to the bacteriological era and the rise of microbe-hunting, disease and health had been viewed in far more holistic terms, he pointed out. In particular, he argued, epidemics were seen as being due to a “unique configuration of circumstances”. Contrasting this configuration model with the notion of disease as “contamination”, Rosenberg invoked a view of health as a “balanced, integrated, and value-imparting relationship between humankind and its environment”.8
It was a similar sensibility that towards the end of his career saw Dubos focus increasingly on interactions between man and his environment and to emphasize what he called the “symbiosis of earth and humankind”.9 In Dubos’s day, these perspectives found expression in the image of earth as a “spaceship” adrift in a hostile universe, and his call for environmental activists to “think globally, act locally”. Today, these ideas find their correlate in the notion of “planetary health” and the call by young activists such as Greta Thunberg to adopt a more holistic and environmentally responsible attitude to our interactions with nature and the lives that depend on it, our own included.10
Lurking in the background, informing our response to Covid-19 and whatever other pandemic might be heading our way during the next one hundred years, is the ghost of Spanish flu. If anything has taught scientists the value of caution and the perils of hubris it is the long shadow cast by the 1918-19 influenza pandemic – what the WHO, an organization not known for hyperbole, calls the “most deadly disease event in the history of humanity”. Since it became possible to retrieve viral genetic material from the H1N1 pandemic virus using modern molecular pathology techniques, virologists have made huge progress in understanding the factors that made the Spanish flu so virulent. By comparing the 1918 virus to descendent H1N1 strains still in circulation, scientists have also come to a better understanding of its epidemiology and pathophysiology. Moreover, the 1997 outbreak of H5N1 bird flu in Hong Kong, and the subsequent outbreaks of other varieties of bird flu in China and Southeast Asia, have shown that it is not necessary for an avian influenza virus to transit through an intermediary mammalian host first in order for it to be the cause of morbidity and deaths in humans. At the same time, the 2009 scare over the “Mexican” swine flu demonstrated that from time to time different swine and human lineages of H1N1 can recombine to produce new pandemic viruses. However, so far, no bird flu or recombinant swine flu virus has yet managed the trick of wide infectivity and high virulence that was achieved in 1918. Furthermore, while it is known that the H1N1 Spanish flu was infectious to all age groups in 1918-19, scientists are still no closer to solving the riddle of why it proved relatively more deadly to young adults, or why mortality rates were closely associated with the increased incidence of secondary bacterial infections. The result is that despite the tremendous advances in microbiology, immunology, vaccinology, and preventive medicine in the century since 1919, influenza researchers are still no closer to being able to predict when new pandemic strains will emerge or how they will impact human populations. As David Morens and Jeffrey Taubenberger put it: “In recent decades, pandemic influenza has continued to produce numerous unanticipated events that expose fundamental gaps in scientific knowledge … These uncertainties make it difficult to predict influenza pandemics and, therefore, to adequately plan to prevent them.”11
That is why, reviewing the last hundred years of epidemic outbreaks, the only thing that is certain is that there will be new plagues and new pandemics. It is not a question of if, but when. Camus was right. Pestilences may be unpredictable, but they will recur.
留言
張貼留言