The Coming Plague: Newly Emerging Diseases in a World Out of Balance

“Disease cowboys” is a phrase Garrett uses to designate a class of doctors active from the 1950s to the 1980s who did fieldwork around the world and often undertook great personal risks to stem the rising tide of new infectious outbreaks. This includes many of the leading players in the stories of The Coming Plague, such as Karl Johnson, Joe McCormick, Daniel Tarantola, and Peter Piot. In Garrett’s view, their on-site research gave them a broad understanding of multiple fields of disease management—from ecology to immunology to tropical disease—that was not available through the conventional, highly-specialized medical training common in the US. With the passing of the disease cowboys’ generation, other medical professionals have lost a robust and holistic view of disease emergence and management.

Drug resistance refers to an adapted state of microbial life in which a set of microbes has gained the ability to withstand medications that previously would have killed or restrained them. All three classes of microbes (bacteria, viruses, and parasites) have shown the ability to gain drug resistance over time, either by random mutations in which organisms that have protective genes against certain drugs survive and pass on their resistance to new generations or by activating cellular defenses and backup DNA segments to respond to a new threat. Garrett presents drug-resistant microbes as a growing danger to human health because many previous classes of medications used to treat them are now ineffective, and in some cases, no other treatment options remain.

Ecology is the study of how living things interact with one another in an environment, and it lies at the heart of Garrett’s main points in The Coming Plague. She argues that humans have too often viewed themselves and microbes as being in two entirely separate categories of being, such that diseases appear to be abnormal, which afflicted us from the outside. In contrast, she paints a picture in which humans and microbes coexist as organisms in the global environment together and that—as in all ecologies—our relationship with them consists of a balancing act. When humanity changes its behavior or the environment, this represents an ecological shift that disrupts the balance of other organisms, and we should expect that they will respond with changes of their own. In the case of microbes, those reactive changes often manifest themselves in new outbreaks of disease.

An epidemic is an outbreak of an infectious disease within a population in a short amount of time. The definition of an epidemic varies in relation to the baseline prevalence of a given disease, such that the outbreak of a rare disease might be called an epidemic after only a small number of cases, while a common disease would require many more cases before being labeled an epidemic. The word is used interchangeably with “outbreak,” which carries essentially the same meaning without being tied to the technical parameters of case numbers.

Microbe is Garrett’s word of choice when discussing the diseases in The Coming Plague, all of which represent microbial infections. In Garrett’s use, “microbe” refers to disease-causing agents in three categories: bacteria (a class of tiny, single-celled organisms), viruses (vehicles of disease-causing genes), and parasites (other microscopic organisms). Microbes are thus microscopic disease agents that are alive or bear the genetic material characteristic of life. This is in contrast to non-living causes of disease like chemicals, genetic impairments, or environmental influences.

In the scientific study of infectious disease, a “reservoir” is the natural host of a disease-causing microbe, often an animal species. The microbe does not cause serious disease in the reservoir species but is usually present in significant numbers, such that contact with another species can result in spillover events. Once a spillover has occurred, the new species that carries the microbe can be severely affected by disease, as it will likely have no natural immunity that the reservoir species bears.