Summary

Bryson begins Chapter 20 by making the point that many diseases remain a mystery to medical science. He uses the example of Akureyi disease, first noticed in a city in Iceland in 1948, for which no cause or treatment has ever been found. “Infectious diseases, as you will gather, are curious things,” Bryson writes (320). Some diseases appear at random and then go quiet. Others advance quickly across landscapes, such as West Nile virus. Some diseases wreak havoc and then mysteriously disappear, such as the sweating sickness that appeared in England between 1485 and 1551. “Baffling outbreaks, particularly small ones, are more common than you might think,” Bryson writes (320). There are four factors that turn a disease into an epidemic: how lethal it is, how good it is at finding new victims, how difficult it is to contain, and how susceptible it is to...