Pandemic: Tracking Contagions, from Cholera to Ebola and Beyond by Sonia Shah Sarah Crichton Books/Farrar, Straus and Giroux, 271 pp., $26.00

Pandemics—the uncontrolled spread of highly contagious diseases across countries and continents—are a modern phenomenon. The word itself, a neologism from Greek words for “all” and “people,” has been used only since the mid-nineteenth century. Epidemics—localized outbreaks of diseases—have always been part of human history, but pandemics require a minimum density of population and an effective means of transport. Since “Spanish” flu burst from the trenches of World War I in 1918, infecting 20 percent of the world’s population and killing upward of 50 million people, fears of a similar pandemic have preoccupied public health practitioners, politicians, and philanthropists. World War II, in which the German army deliberately caused malaria epidemics and the Japanese experimented with anthrax and plague as biological weapons, created new fears.

In response, the US Centers for Disease Control (CDC), founded in 1946 to control malaria domestically, launched its Epidemic Intelligence Service in 1951 to defend against possible biological warfare, an odd emphasis given the uncontrolled polio epidemics raging in the 1940s and 1950s in the United States and Europe. But in the world of public health, the latest threat often takes precedence over the most prevalent.

According to the doctor, writer, and philanthropist Larry Brilliant, “outbreaks are inevitable, pandemics are optional.” Brilliant, a well-known expert on global health, ought to know, since he has had much to do with smallpox eradication. Smallpox, arguably the worst disease in human history, caused half a billion deaths during the twentieth century alone. The strain called Variola major—the most lethal cause—killed one third of all infected and permanently scarred all survivors. In 1975, Rahima Banu, a two-year-old Bangladeshi girl, became the last case of V. major smallpox. Two years later, Ali, a twenty-three-year-old hospital cook in Somalia, became the last case of V. minor. Rahima and Ali survived. Smallpox did not.

Forty years later, smallpox is still the only disease affecting humans ever to have been eradicated. (Rinderpest, a virus affecting cows—literally “cattle plague”—was eradicated in 2011.) There is optimism that polio and guinea worm may soon follow. Meanwhile, dozens of new infectious diseases have emerged, including the pathogens behind the twenty-first-century “pan-epidemics”—a term coined by Dr. Daniel Lucey to describe SARS, avian flu, swine flu, MERS, Ebola, and now Zika.

The fear, fascination, and financial incentives that these new diseases create divert attention and resources from ancient diseases like cholera, malaria, and tuberculosis, which infect and kill far more people. Ebola has caused relatively few deaths, while TB infects 9.6 million people each year and kills 1.5 million, and malaria infects more than 200 million, killing nearly half a million. (Ali, smallpox’s last survivor, later succumbed to malaria.)

Zika virus was…