AVIAN INFLUENZA, the so-called bird flu, has been described, by various people who should know these things— spokespeople from the World Health Organization (WHO) and the United States’ Centers for Disease Control and Prevention— as the single greatest threat facing the world. Not war, not poverty, not starvation, not catastrophic climate change. Bird flu.
Okay, let’s play a bit of Bill Clinton here. What do these authorities mean by “threat”? (We should also ask what they mean by “bird” and “flu,” but that is a story for another time.) Let us begin with “threat.”
A threat, in this sense, is something that is likely to cause us harm; we could also use the word “danger.” Bird flu is the biggest danger facing the world, these authorities are saying, and to deal with this threat, better security is needed. Until a few years ago, we scientists had banished words like “threat” and “danger” and reduced them to the more scientifically controllable, measurable word “risk.” Our response to danger was called “risk management.” Now, in the new age of emerging infectious diseases such as bird flu, we seem to be back in the jungle. We are back to dangers and threats. The worst of these, today’s equivalent to the man-eating lion in the dark forest, is a pandemic. The word “pandemic” is often bandied about in the same conversations as “threat.” One of my colleagues has defined a pandemic as an epidemic, only “huger,” which is as accurate a description as any.
So what is an epidemic? It is like an outbreak, only huger. An outbreak occurs when a relatively small group of people or animals or plants gets sick, as when everyone gets sick after eating a warm potato salad on a sunny day. The source of an outbreak can usually be traced to one particular event or exposure.
The word “epidemic” goes at least as far back as Homer, in about the eighth century BC. Homer used it to refer to someone in his or her own country, as differentiated from a traveler. It had connotations of “indigenous” or “endemic.” Hippocrates, in 430 BC, gave it a medical slant, referring to physical syndromes (illnesses) that occurred in particular places and times. After the discovery of bacteria in the nineteenth century, people began to use the term to refer to specific diseases, as in epidemics of cholera. More recently, the word has been used to refer to more cases than expected of both very specific diseases, such as hemolytic uremic syndrome caused by E. coli O157:H7, and general syndromes, such as obesity. In this book, I shall assume that an epidemic occurs when many people or animals get sick and perhaps die, usually countrywide.
A pandemic is a lot of people getting sick and dying in many countries at more or less the same time. In response to the threat of avian influenza, WHO recently updated its criteria for what it calls a pandemic. Its classification includes an Inter-Pandemic Phase (which thus assumes we are always between pandemics, as we are between ice ages), in which other animals, but no people, are infected and ranges up through various Pandemic Alert phases, in which the agents from other species are trying us out but haven’t fully adapted to us, to Phase 6, the Pandemic Phase, in which there is “increased and sustained transmission in the general population.” After that, waves of the disease go around the world, but fewer people get sick and die with each subsequent wave, either because humans have built up immunity or because the agent, defying creationists, evolves through the process of natural selection. In this case, only those with milder forms of the disease survive long enough to pass it on to others, and hence the agent moves in with our species to a longer, gentler, more sustainable life. Finally, through some combination of heroic efforts on our part and the natural progression of events, we arrive at another Inter-Pandemic Phase.
When we say that a lot of people are getting sick or dying, what do we mean? How many people is a lot of people? What do we mean by “sick”? Epidemiologists sometimes define an epidemic as more cases than they would expect, or as “unusually high rates” of disease or death. What is “unusual”? What is “unexpected”? How, indeed, does one measure the importance of a disease?
Each year there are several hundred million cases of malaria, and a million or so people die, mostly children. Tuberculosis kills a couple of million people a year. HIV/AIDS and AIDS-related illnesses kill millions every year. Diarrhea kills millions of children every year. Some diseases have a high case-fatality rate, meaning that a large proportion of those who get the disease die. Some of these diseases affect only a few people, and so the fatality rate in the overall population is very small. Other diseases have low case-fatality rates, but many people are infected, so the total number of people who die in the population is very high. Many global assessments by the World Health Organization, the World Bank, and other large organizations now use measures such as disability-adjusted life years (DALY) and disability-free life expectancy (DFLE) to compare the importance of various diseases. Using these measures emphasizes afflictions of children (who have more years of life to lose than older people), such as diarrhea, malaria, suicide, and accidents. These measure also give greater weight to chronic, debilitating diseases than to acute outbreaks. How do we assess importance? Is it a scientific decision?
Are authorities more hesitant to use the loaded word “pandemic” for some diseases, preferring to speak of a “global epidemic” of AIDS or “high rates” of malaria or diarrhea in certain parts of the world? If so, why is that? Do some diseases so radically and explicitly expose global economic inequities that the wealthy owners of global institutions would prefer to focus on those that more directly threaten Europe and North America and for which a technical, money-making fix is more likely to be found? The truth is that although words like “outbreak,” “epidemic,” and “pandemic” have a scientific ring to them, and some grounding in science, their use is very political.
I don’t want to belittle the possibility of a pandemic of some sort of plague. Indeed, by the time you read this, perhaps that plague will be upon us. I just want us all to understand that, in the way we talk about and respond to diseases in the world community, we are going beyond science to make value judgments about what is unexpected or unusual. In one sense, every death is expected and tragic. Baby-boomer optimism about technological breakthroughs notwithstanding, death is, and will remain, the usual course of events. The world could not unfold as it should if we did not all, sooner or later, die. This eventuality is what gives us despair and our children hope. We have come to expect that our deaths will occur later in life, however, and by heart attacks, cancer, suicide, or car accidents (which are on the top ten world killer list), not attacks of chicken viruses, for goodness’ sake.
There is a measure of poetic justice in the idea that the next global pandemic could come from chickens, that they should make us even more fearful than the explosive strutting of half-cocked fanatics that attempted to hijack the global story after 2001. We, industrial societies, have been the ones who called for a chicken in every pot. In our conquest of hunger and pursuit of obesity, we were the ones who pushed for economies of scale in agriculture, which not only brought down the consumer price of good protein but created vast brewing vats for a multitude of infectious microbes. Chickens have been on the front line of our battles against nature and hunger—and our fanatical obsession with personal health, low taxes, and the economics of me-ism. This is, then, the revenge of the pawns.
In this current avian influenza scenario, the chickens really are like pawns, since they are only the messengers from a beleaguered biosphere to cocky human beings. So far, the general response has been to shoot the messengers. If we want to stay around in a convivial world, our species shall have to do better; we shall have to come to some accommodation with the kings and queens and bishops hiding in the back row. This is not a battle to win. The best we can hope for is an uneasy, mutually respectful draw.
The flu pandemic could kill a billion people, or maybe just a few dozen. If it is a real killer, by the time we know (the viruses change so fast that we won’t know until they are upon us), it will be too late to make a vaccine. By the time the vaccine would be produced, those who are going to die would already be dead. Scientists and public health workers think there is a pandemic coming, but they are not sure. No one knows which agent it will be or where it will come from. The better the detection methods become, the more precise the tests, the more refined the technology, the more viruses and other tiny living things can be seen— the less is known about what they mean.
Emerging infectious diseases such as avian influenza have created a dilemma for scientists: what we know we don’t know seems to be expanding faster than what we are pretty sure we do know. We have a lot of hard facts and a poor understanding of what they mean. What kind of advice can be given to policymakers? How can scientists and politicians incorporate a sense of uncertainty and ignorance into their activities? How do we do this and still whistle while we work?
There are ways, but they are ways that many scientists and most politicians have been trying to ignore. Twenty-first-century problems cannot be solved using only nineteenth- and twentieth-century scientific methods, and there is a kind of child-like simplicity in supposing they can. Many scientific methods require us to put on blinkers and focus on small things. A lot can be learned by studying the genetics of viruses and the structure of human cells, but the questions now facing the world are bigger: Where does a pandemic come from? Can it be predicted or prevented, and, if not, what is the best way to respond and adapt? How can people live in healthy peace with nature on this planet? These questions require a combination of the best laboratory science with an understanding of ecology, culture, social change, and ethics. This is no time to put on blinkers, either running to the apocalyptic and conservative religious and economic cults that daily evangelize in the headlines or retreating to the kind of experimental laboratory science that was excellent at solving an entirely different set of problems. Humanity has come too far, learned too many good things, to make that retreat.
Avian influenza is only one of a great many zoonoses, some of which have changed the course of history and some of which circulate among us undetected—sleeper cells, perhaps, or maybe just small sleeping companions. Occasionally, in small acts of generosity, we share them back.
WHO defines zoonoses as those diseases caused by agents that are naturally transmitted between other vertebrates and humans. The late Calvin Schwabe, a zoologist, veterinarian, epidemiologist, medical anthropologist, humanist, chef, and pioneer in the study of what has been called “one medicine”—the common historical roots and substantive relationships between human and animal medicine—took a slightly more liberal view of zoonoses. In his Veterinary Medicine and Human Health, he defined zoo-noses as diseases whose agents are shared in nature among people and other vertebrate species. His definition thus includes not just infections transmitted from vertebrate animals to people, but also a wide array of diseases that people and other animals have in common because of environments they share, as well as diseases that occur because animals create hospitable environments for human pathogens, even though the animals may not necessarily serve as reservoirs, nor transmit the agents directly to people. Pedro Acha and Boris Szyfres, writing for the Pan American Health Organization, worked around some of these ambiguities by entitling their major text in the area Zoonoses and Communicable Diseases Common to Man and Animals.
Reservoirs for zoonoses are their natural home—those animals or combination of animals and ecosystems in which the infectious agents usually live and multiply and on which they depend for survival. If the reservoir is a single animal, it’s called a reservoir host (which should mean, if life were fair, that we would call the microbe a guest, which we don’t; we denigrate it by calling it a parasite or pathogen). Microbes usually don’t kill their reservoir hosts, or, if they do, they take a while to do so, or they find ways to get themselves transmitted to another animal (through biting or contaminating the environment, for instance) before the first animal dies.
Most often, humans are “accidental” hosts of the agent (as if, in other types of diseases, we are deliberately targeted). If we are “accidental hosts,” the microbe doesn’t need us; we just happen to provide a handy bed-and-breakfast while it is looking for someone else. Sometimes we are a dead-end host, a kind of Hotel California, from which the agent can check out but never leave (alive, that is).
Zoonoses may be classified according to the animals that are their natural homes, such as chickens, dogs, rodents, bats, or non-human primates. This classification helps us to think carefully about the species with which we interact, how we interact with them, and how we might manage those interactions. People provide opportunities for zoonoses by creating habitats for some types of animals (raccoons and pet cats, for instance, in urban environments, or white-tailed deer and cows in North American farmland) or by invading the habitats of other animals, such as bats, wild primates, or migrating birds.
We increase the chances that an organism will jump across species when we interact more closely with those species. About four hundred free-ranging rhesus macaques live at the Swayambhunath Temple in Kathmandu, Nepal, interacting with residents and visitors by sharing water, food, and aggressive play. Scientists have only begun to investigate the disease risks associated with such temples, common throughout South and Southeast Asia. In North America, people play with their pet dogs and cats or take them into hospitals in animal visitation programs, raising similar questions. The stakes are raised if we engage in that most intimate contact of all—eating another species. One theory of the emergence of HIV/AIDS is that people killed and ate non-human primates from which they picked up the virus. Why people would dine thus—being marginalized, poor, and driven into the forest margins—is part of the larger story, which I hope becomes apparent as you read this book.
Zoonoses may also be classified ecologically, according to the cycles of infection that maintain them in nature and the ways they are communicated between animals and from other animals to people. Direct zoonoses, which include many food-borne agents like Salmonella and E. coli O157:H7, may be perpetuated in nature by a single vertebrate species, such as birds or cattle; their natural cycles require no invertebrates, and they are transmitted to people directly, through bites or food. This book will not dwell on food-borne zoonoses; those diseases, including newly emerging ones such as bovine spongiform encephalopathy (mad cow disease), will be covered more thoroughly in the forthcoming second edition of my book Food, Sex and Salmonella.
Cyclozoonoses have maintenance cycles that require more than one vertebrate species but no invertebrates. Echinococcus multilocularis, a parasite found in dogs, is an example.
Metazoonoses require both vertebrates and invertebrates, such as ticks or mosquitoes, to complete the life cycle. The plague, which needs fleas, and American sleeping sickness, which requires triatomid bugs (also called kissing bugs), are meta-zoonotic diseases.
Finally, saprozoonoses depend on inanimate reservoirs or development sites, such as soil, water, or plants, as well as vertebrate hosts. Some of the parasitic diseases we get from our pets, like toxoplasmosis and toxocariasis, require an external environment to complete their life cycles; their eggs do not become infectious for another animal until they have “ripened” in the environment for days to weeks.
Other saprozoonoses, which aren’t zoonoses by the WHO definition, grow in the environment, from which they make people and other animals sick. In 2001, for instance, dogs, cats, harbor seals, porpoises, ferrets, llamas, and people in and around a particular area of Vancouver Island all suffered serious lung and neurological infections from an environmental fungus called Cryptococcus gattii. Interestingly, the strain of the fungus that caused the outbreak usually lives in the tropics and subtropics. Some people suggested climate change might have contributed to its spread. This book does not dwell on such diseases but focuses on diseases we get from animals rather than those we get with animals.
To the classifications above, laboratory scientists would add a system differentiated according to bacterium, virus, and parasite species. In this book, I have used a variation on the ecological and animal-reservoir themes. It has a separate section for each of the following types of zoonoses: those that involve insects and a variety of other animals, but no birds (“And Scurrying Beasties”); those that involve birds, with or without insects (“Of Singing and Flight”); those that involve rats and bats (“And Things That Go Bump in the Night”); and those that involve animals that we have domesticated and with which we have evolved especially close relationships (“With All Our Most Constant Companions”). It is thus a hybrid classification system based on animal reservoirs, natural cycles, and the relationships of the animal reservoirs to people. It seemed to me to best reflect how intelligent non-scientists might classify them and begin to make sense of them.
Some zoonoses have been around for a long time and will be for millennia to come; our species should live so long. Microbes of all sorts, all those microscopic “animalcules” that the Dutch scientist Anton van Leeuwenhoek first saw through his microscope in the late 1600s, are all around us, in our mouths, on our genitals, on our hands. And certainly all over those other animals with which we share the planet. Your dog could be carrying them, or your cat, or the mosquitoes zinging around your ear as you read this book on the veranda in the evening; they could be in your salad or in those cute raccoons waddling across the backyard. The diseases caused by these microbes have names that are both familiar and odd and include the plague, West Nile virus infection, Lyme disease, sleeping sickness, salmonellosis, poker players’ pneumonia, and tuberculosis. These diseases can—and do—strike many people every day. They show up as worms in the eye and cysts in the belly, chronic heart disease, and debilitating infections of the brain.
Usually zoonoses drive through our neighborhoods and check us out without our even knowing. We then, as some researchers have said, “suffer” from subclinical disease. Not every infection (when the bug gets into you and multiplies) results in clinical disease. Sometimes these infections do kill. Most often they cause a passing, “flu-like” illness.
The more perceptive among my readers will have noticed a little trick I have been playing in the last few paragraphs. I have been slipping back and forth between diseases and infections, and between animals and people. When we speak of pandemics of diseases people get from animals, we need to be more careful. It is possible to have a pandemic infection in animals or people without a lot of disease. Infection does not equal disease. Infection in animals does not equal disease in people. Thus, we would prefer that if there is a pandemic, it be a pandemic of infection in animals (which avian influenza already is), or at least a pandemic disease in birds (which it already is), but not a pandemic disease in people.
Some writers differentiate these by using the terms “epizootic” and “panzootic” to refer to epidemics and pandemics in animals other than people. Although this usage simplifies some things for bureaucrats and managers, it obscures the fact that people are animals—exceptional animals, to be sure, but animals nonetheless—and that the sharing of microbes among species is normal. The “——demic” and “——zootic” allows people to fall back too readily into a kind of delusional silo mentality. No realistic understanding of zoonoses and their control can be achieved without the contributions of natural scientists (ecologists, entomologists, and zoologists, for instance), health scientists (veterinarians and physicians), historians, anthropologists, social scientists, artists, and just plain folks.
The bad news is that many of the threats of disease we face today are connected to each other—and to many of the things we have come to cherish in our modern lifestyles. The way we deal with one disease, or even one so-called problem, can have far-flung consequences for what happens to other diseases and other problems. The good news equally is that many of the threats of disease we face today are connected to each other—and to many of the things we have come to cherish in our modern lifestyles. The way that one disease or problem is dealt with can have far-flung consequences for what happens to other diseases and other problems. As Douglas Adams realized when he wrote The Hitchhiker’s Guide to the Galaxy, the answer to the question of “life, the universe and everything else” is relatively simple and hard to get our heads—and our lives—around. It may not be “42,” as the computer in the novel suggests, but it is not necessarily billions of dollars of better biomedical technology and vaccines, as others propose. Some of our other options will become apparent in the tales in the book.
Let us begin, then. And what better way to begin than with the plague.