Beasts of the Earth: Animals, Humans, and Disease

Beasts of the Earth: Animals, Humans, and Disease

Beasts of the Earth: Animals, Humans, and Disease

Beasts of the Earth: Animals, Humans, and Disease


Humans have lived in close proximity to other animals for thousands of years. Recent scientific studies have even shown that the presence of animals has a positive effect on our physical and mental health. People with pets typically have lower blood pressure, show fewer symptoms of depression, and tend to get more exercise.

But there is a darker side to the relationship between animals and humans. Animals are carriers of harmful infectious agents and the source of a myriad of human diseases. In recent years, the emergence of high-profile illnesses such as AIDS, SARS, West Nile virus, and bird flu has drawn much public attention, but as E. Fuller Torrey and Robert H. Yolken reveal, the transfer of deadly microbes from animals to humans is neither a new nor an easily avoided problem.

Beginning with the domestication of farm animals nearly 10,000 years ago, Beasts of the Earth traces the ways that human-animal contact has evolved over time. Today, shared living quarters, overlapping ecosystems, and experimental surgical practices where organs or tissues are transplanted from non-humans into humans continue to open new avenues for the transmission of infectious agents. Other changes in human behavior like increased air travel, automated food processing, and threats of bioterrorism are increasing the contagion factor by transporting microbes further distances and to larger populations in virtually no time at all.

While the authors urge that a better understanding of past diseases may help us lessen the severity of some illnesses, they also warn that, given our increasingly crowded planet, it is not a question of if but when and how often animal-transmitted diseases will pose serious challenges to human health in the future.


This book is about human infectious diseases and the microbes that cause them. As the recent resurgence of AIDS, tuberculosis, and influenza has shown, infections are still major causes of illness and death in our society. We are also discovering that infectious agents may play a role in many chronic ailments such as cancer, heart disease, and schizophrenia. The microbes that cause infectious diseases are thus very much part of our daily lives.

The vast majority of these microbes has been, and continues to be, transmitted to humans from other animals. A few diseases, heirloom infections such as those caused by herpes and hepatitis viruses, first infected our primate ancestors, and their microbes descended through early hominids to Homo sapiens. A large number of diseases, such as measles and tuberculosis, resulted from microbes transmitted to humans following the domestication of animals. Many other diseases, such as AIDS, SARS, mad cow disease, monkeypox, and bird flu have been transmitted from animals to humans in recent years as the relationship between animals and humans has changed. Each change in this relationship is accompanied by a risk of additional animal microbes being transmitted to humans.

We have become accustomed to thinking of animals as our friends, not as sources of human disease. Through the influence of Aesop, the Brothers Grimm, Beatrix Potter, and Walt Disney, it has become increasingly difficult to appreciate that the animal represented by Donald Duck was the origin of an influenza pandemic that killed twenty million people, that Mickey Mouse may be spreading deadly hantavirus, that Clarabelle Cow is the source of prions that cause mad cow disease, and that Pluto may be carrying leishmaniasis. We do not associate Bambi with Lyme disease, Big Bird with West Nile virus, Rocky Raccoon with rabies, or Garfield with toxoplasmosis. Even Barney, the dinosaur beloved of small children, is almost certainly a carrier of Salmonella bacteria, as all reptiles are.

In the past two hundred years, we have entered another period in which . . .

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