Wild Health How Animals Keep Themselves Well and What We Can Learn From Them Trade cloth - 2002

Details

• Title Wild Health How Animals Keep Themselves Well and What We Can Learn From Them
• Author Cindy Engel
• Binding Trade Cloth
• Edition 1st Printing
• Language EN
• Publisher Houghton Mifflin, Wilmington, Massachusetts, U.S.A.
• Date January 16, 2002
• ISBN 9780618071784

1 HEALTH IN THE WILD The multitude of the sick shall not make us deny the existence of health.
— Ralph Waldo Emerson, 1860

The herbalist Juliette de Badracli Levy has spent much of her long life observing the way animals keep themselves well in the wild. In one of her many books she writes, “Everywhere in the woods one observes the wild animals rearing their young in health and freedom from sickness.”1 But this view is considered naively romantic by wildlife health experts. Although an animal may seem healthy on the surface, it may harbor diseases and parasites that drain its resources and can flare up should resistance falter momentarily. Furthermore, the animals we see are the survivors, disease and death having filtered out the less healthy. The wild animal, from this perspective, fights a perennial battle with sickness and disease.
Which view is correct—the romantic vision of a healthy and harmoniously balanced ecosystem, or the survivalist vision of a ruthless, endless battle with death and disease? Paradoxically, the two views are not as diametrically opposed as they might first appear. When we see a beautiful swan glide across still water, the movement appears effortless; the swan seems calm and untroubled, even serene. An observer below the water, however, would see that the swan is working hard: muscles are contracting and relaxing; legs and webbed feet are pumping, pushing water aside with great effort. So it is with wild health. While an animal may appear to glide effortlessly through life’s troubled waters, a continuous struggle for survival goes on, largely unseen. One perspective, then, is that behind a façade of blissful, harmonious balance, each and every organism is working to maintain its health and to survive. Another perspective is that the struggle and selective survival actually create the impression of harmony. I find no conflict in being able to see both the struggle and the balance in the same vista, but evidently the answer to the seemingly straightforward question “How healthy are wild animals?” is influenced by the perspective of the observer.
Most of us gain our impressions of health in the wild primarily from the news media—and news about wildlife, like news about anything, is seldom good news. Currently, wildlife health makes grim reading. Seal and dolphin populations in the Mediterranean and Baltic seas, and in the coastal waters of the United States, have been seriously affected by major disease outbreaks. It looks as if the butylins used to protect the hulls of ships from barnacles and such are the main culprits. These biocidal chemicals damage mammalian immune systems, lowering resistance to disease and cancers. Meanwhile, harbor porpoises in the English Channel and southern North Sea are sickened by the high concentrations of polychlorinated biphenols and mercury in their waters. And a global epidemic of mysterious tumors affecting endangered sea turtles is linked to the pollution of their watery breeding grounds.
On land, amphibians around the world are facing a health crisis. Over the past two decades there has been a rapid decline in their numbers, including extinction of some species, apparently because of a global epidemic of a particular fungal infection. Furthermore, the number of grossly abnormal amphibians born has increased. Although the exact causes of this crisis are ambiguous, environmental factors that disrupt both disease resistance and the developmental systems of amphibians may play a role. All the main contenders are caused by humans: global warming, agrochemicals, and damage to the ozone layer.
Pollution distorts our impression of wild health, and the occurrence of disease in wild-animal populations has become an important indicator of ecological disruption. For a clearer picture of how animals stay well, we need to assess the health of populations far from the effects of industrial society. But even there our presence can disrupt the survey. Early in the study of wild chimpanzees at Gombe National Park in Tanzania, a polio outbreak decimated the chimpanzees, killing four and leaving six permanently disabled. It is thought that the virus spread from local humans, who suffered a polio outbreak a month before, and was carried inadvertently by vaccinated human scientists. The introduction of new pathogens can be devastating for any population. The Spanish conquistadors of the fifteenth and sixteenth centuries killed most of the native Central Americans, not by superior warfare or cunning intellect, but by bringing with them novel and consequently lethal diseases (measles, for one). Today pathogens are traveling the world with increasing ease as the internatiional trade in food, plants, and animals expands, and humans become increasingly mobile. As a result, wildlife is exposed to many new diseases.
As thhhhhe human population increases, the need for more and more land for housing, agriculture, and tourism continues to squeeze wildlife into ever-shrinking areas of natural habitat. Asian elephants no longer have enough room to find the food and water they need to stay well. Lions in the Serengeti National Park, along with the last few viable populations of African wild dogs, have been ravaged by canine distemper virus and rabies caught from domestic dogs skirting the edge of the park. William Conway of the Wildlife Conservation Society puts it succinctly: “Our growing herds and flocks of domestic animals have become a plague to wildlife, devastating habitat and spreading disease.” We hear far more about disease passed in the other direction— from wild to domesticated animals. In Europe, wild badgers are blamed by farmers for infecting domesticated cattle with tuberculosis, deer are feared as carriers of foot-and-mouth disease because infected herds can remain symptom free, and wild boar are hounded for spreading classical swine fever (CSF) to commercial pigs because “CSF has become milder in wild boar than pigs.”3 In North America, free- ranging bison are accused of spreading brucellosis to ranched cattle, and wild deer of spreading tuberculosis to cattle. In what I consider to be a totally illogical response, wild animals successfully keeping disease at bay are often killed in order to protect sickly (but profitable) domesticated livestock from infection. In the United Kingdom, for example, a culling program is currently under way in which twenty thousand badgers will be killed to prevent them from possibly spreading tuberculosis to cattle.
This fear of wild animals as harbingers of disease is deeply ingrained in the human psyche. The European hedgehog (small, spiny heroine of a classic Beatrix Potter story) was recently described as “among the most dangerous animals in Europe” by pathologist Ian Keymer of London Zoo, who found that they carry at least sixteen diseases known to affect people. And those “could be the tip of the iceberg,” he adds. “If we look closer we may find many more.” Howard Hughes would have understood, but if we follow this line of reasoning to the extreme, we should never exchange air or body fluids with other people, and we should certainly eradicate all other species on earth—just to be safe!
Even though wild animals are able to carry diseases that affect livestock and humans, it would seem sensible to explore why they are so successful in fending off the worst effects of these diseases, to look to them for ways of improving our own health and that of our livestock, rather than trying to eradicate them. In addition to looking at genetic resistance to disease, we would do well to learn from the many behavioral self-help strategies that wild animals employ.
One difficulty in assessing wild health is locating genuinely wild places—where animals are not confined by perimeter fences, culled, managed, or exposed to domestic animals or humans. Where is the wild truly wild? Unfortunately, such habitats are shrinking daily. A survey by the World Wide Fund for Nature found that more than a third of the planet’s animal and plant species exist exclusively on a scant 1.4 percent of its land surface.5 Moreover, few places on earth remain uncontaminated by persistent pollutants such as PCBs, dioxins, and DDT. With shrinking habitat and increasing pollution, the opportunity to study undisturbed animal populations is decreasing, while the need to do so becomes ever more urgent.
Even when we can find truly wild places, measuring or assessing the health of animals living there is notoriously difficult. Most of the evidence has tended to come from the incidental comments of natural historians and scientists on the health of animals being observed. In the early 1960s George Schaller, of the New York Zoological Society, was the first person to study wild lowland gorillas in West Africa. He found them healthy, lean, well muscled with shiny coats, although he noted that they did catch cold when the rains came. He was surprised to find roundworms in half the fecal samples he examined because the gorillas were in such good health. During the same time, Jane Goodall found wild chimpanzees to be generally healthy, although they too quite often suffered from colds and coughs during the rainy season. In the 1970s Cynthia Moss started her long-term study of elephants in Amboseli National Park and found them in extremely good health. (Things went wrong in later years, though, when human encroachment and drought struck the herds.) They had few diseases and only a few cases of unexplained sickness. They rarely suffered from contagious epidemic diseases, such as rinderpest, and were able to live to a ripe old age as long as they could avoid drought and human hunters.
Schaller later went to Kanha, in India, where he found disease rare among free-ranging, well-nourished chital (medium-sized deer) and gaur (wild relatives of the cow). He concluded that the health of domestic and wild hoofed animals is mainly a function of the quality of the range, and that animals in poor condition as a result of malnutrition become highly susceptible to parasites and disease. Similar conclusions have been drawn by wildlife veterinarians, who report that free-living marsupials in Australia have few problems with infectious diseases, parasites, and cancers, unless droughts, floods, or range restriction occur.
Unfortunately, anecdotal observations such as these are not adequate to provide an accurate scientific picture of wild health. Sick animals may alter their behavior in ways that make them harder (or easier) to spot than healthy animals. Sick elephants, for example, often separate from the herd to remain near water, shade, and easy food, so an observer might underestimate the prevalence of sickness. Hedgehogs, normally nocturnal, when sick will sit in the sun during the day. A daytime observer might therefore think that hedgehogs were more sickly than they are. More visible populations can be taken as representing a species when this is not necessarily so. Red foxes in the United Kingdom have moved into cities where food is more plentiful and energy rich. These urban foxes live in conditions much more crowded than their rural counterparts, because the food supply is more concentrated. The health of the more visible urban foxes is therefore not an accurate indication of the health of wild foxes in their natural habitat.
Fortunately we are now seeing a minor flurry of health assessments of wild animals living in some of the remotest parts of the world, far from human settlements and pollution. In the 1990s the Wildlife Conservation Society’s field veterinary program, headed by William Karesh, ascertained that anacondas in Venezuela, macaws in Peru, rock-hopper penguins and guanacos in Argentina, impala in northern Namibia, forest duiker and pancake tortoises in Tanzania, and African buffalo were all “in good physical condition.” They were muscled and lean, had cleanly healed serious wounds, were harboring surprisingly few internal or external parasites, and showed no signs of physical abnormalities such as those currently seen in amphibians. Blood tests revealed that parrots had few infections with common bird diseases and were successfully carrying avian viruses that commonly wipe out captive parrots. Impala had surprisingly few previous infections with local diseases, and duiker carried serious pathogens such as leptospirosis with no visible ill effects. African buffalo were outstanding in their ability to resist disease: “When buffalo encounter viral and bacterial diseases, they generally suffer little.” They were in excellent health, yet blood tests revealed that they had been in contact with leptospirosis, parainfluenza, brucellosis, bovine herpes, bluetongue, and foot-and-mouth. As successful combatants of such infections, they were considered “carriers” of disease and much despised by local cattle farmers.
These assessments tend to bear out the earlier observations of Schaller, Goodall, and others that wild animals are often infected with disease-causing organisms (pathogens) without showing any symptoms. Repeatedly, animals appear to be in good condition when blood and fecal tests show infection with pathogens or parasites. We have to conclude that it is normal—natural—to be infected with low levels of pathogens and parasites in the wild, but that somehow these are kept below symptomatic levels. Benjamin Hart, a veterinary research scientist at the University of California, Davis, concludes that “wild animals generally are often immune to vector-borne diseases and show few clinical signs of illness from parasite infections.” Whether you consider such animals to be healthy or not depends on whether you think the presence of the pathogen is the same as the presence of the disease. In my view, it is not necessarily the same: to carry pathogens without showing symptoms might be considered a sign of extremely good health. Nor does it matter that these animals are only the survivors—that the unhealthy ones simply failed to make it. It is because they are survivors that they are of interest to us. How is that they have survived and maintained their health while others have not? They are not merely survivors; they are doing very well. We should be interested in any behavior that has contributed to this condition.
My unsurprising conclusion is that when wild animals are free to range over undisturbed habitat, not exposed to high levels of pollutants and not exposed to extremes of environmental change, they are generally in good health. They live within an ecosystem to which their physiology and behavior are, by virtue of their very survival, well adapted. They have been exposed to local pathogens from an early age, so that their immune system is primed (as it would be by vaccinations) for resistance to them. They may get sick; but when they do, the reason is primarily a strong disruption in their environmental conditions (drought, pollution, lack of food, overcrowding, or invasion by a novel pathogen).
Of course, the immune system plays an enormous role in maintaining health, but it is by no means the only line of defense an animal has—and it is certainly not independent of behavior. Scientists at Stanford University captured healthy wild African green monkeys and caged them separately to monitor the effects of stress on their immune systems. The monkeys rapidly succumbed to infectious diseases, and some even died despite being given all the nutrients they were thought to need. This is not an isolated case. It is well documented that healthy wild animals do not take readily to captivity. Immune collapse is common. It is notoriously difficult to maintain the health of wild-born gorillas in captivity even if the animals were healthy when caught. White sharks cannot be held captive at all; they die within weeks.12 The health of the immune system is demonstrably interlocked with the animal’s behavior in its environment.
Good health is therefore a balance between the opposing survival instincts of the individual animal and all the other organisms with which it shares its habitat. The ubiquitous nature of pathogens means that constant attention is needed in order to remain healthy. Animals cannot simply rely on their immune systems to keep them well under constantly changing conditions. They must take an active role in maintaining their own health. Incredibly, although the physiology and immunology of disease are well researched, the behavioral aspects of health maintenance have not received a great deal of attention. (Benjamin Hart has published the only recent reviews on this subject.) Paradoxically, animal health research programs rarely study health. Like human health research, animal health research concentrates on sickness and disease rather than on how or why certain individuals remain healthy in their natural surroundings. Disease processes are usually studied in domesticated species and under sterile laboratory conditions in which the animal is unable to influence the course of the disease. In other words, the study animals are observed passively enduring disease rather than actively managing their own health. Until recently, scientists have not focused on whether animals have any successful strategies for dealing with disease.
To a layman the terms “health” and “fitness” may be synonymous, but to a biologist they are very different. For biologists, fitness is measured by the number of offspring an animal has (that survive to reproduce themselves) compared to other individuals in its population. An individual animal could, therefore, be considered fitter than another if it successfully reared more offspring—even if it was coughing up blood and dragging itself along on paralyzed limbs! Of course, the fittest animal in a population is often (although certainly not always) strong and healthy as well, but the term “survival of the fittest” is frequently misused to refer to strength or health. Even biologists pay little attention to health, considering fitness a far more relevant attribute. However, the ways animals maximize their health is clearly a pivotal mechanism by which they increase fitness. Survival includes the important aspect of quality. Merely surviving is not enough. A wild animal has to survive in as healthy a condition as possible in order to compete successfully with others and reproduce. If behaving in certain ways enhances the health of certain individuals, it will give them an adaptive advantage over others that do not behave in those ways. There need be no conscious, deliberate, or intentional basis to these behaviors.
What aspects of animal behavior are we looking for? Basically, any action that quantitatively prevents or treats ill health. There are several possible approaches. An important aspect of all living organisms is that they manage to keep their insides in a fairly steady state with respect to what is on the outside. It was back in 1857 that the French physiologist Claude Bernard discovered that organisms actively strive to maintain their internal state within a narrow range. This phenomenon, called homeostasis, allows the organism a degree of independence from exterior conditions. Many homeostatic mechanisms are physiological: that is, they involve the processes and functioning of the body. As external temperature increases slightly, for example, a mammal might start to sweat; the capillaries near the surface of its skin dilate so that the blood is cooled near the outside of the body and internal temperature is stabilized. But if these physiological changes do not successfully rebalance body temperature, the animal may change its behavior by seeking shade or lying in cool water.
With this vastly oversimplified example, it is easy to see how physiology and behavior interact to keep the internal state “balanced” and thereby maintain health. Many aspects of health maintenance behavior can be described as homeostatic. Other behaviors such as grooming, resting, or even fasting are best described as self- maintenance. Some actions, though, are only taken in response to a health disruption and are called (unsurprisingly) illness response behaviors. Some involve the animal’s use of a substance not made by itself, in such a way as to rectify malaise, and are therefore called self-medication. Collectively, these health maintenance behaviors are the focus of this book.

Copyright © 2002 by Cindy Engel. Reprinted by permission of Houghton Mifflin Company