Spillover — Animal Infections and the Next Human Pandemic

The book opens with the «pale horse» epigraph from Revelation, but with a rather modest virus. In September 1994, in the Brisbane suburb of Hendra, a pregnant racing mare named Drama Series falls ill; the horses in her stable die one after another, and trainer Vic Rail dies after a week in intensive care. Quammen says he chose this case on purpose: Hendra is not the scariest virus and has killed only a handful of people, but it is «marginal, erratic, but in a larger sense typical» — a good starting point for understanding how new diseases emerge.

The author's method is clear from the first pages: he does not just summarise papers, he goes to the scene. A neighbouring horseman, pouring him instant coffee, recalls horse heads and legs piling up in skips on the street; police taped off the house as a crime scene, since sabotage or insurance fraud was first suspected. The surviving strapper, Ray Unwin, tells him he is «not a whinger» but his health has been «crook» ever since. These human details keep the science alive.

Then the detective work begins. The Australian Animal Health Laboratory isolates a new paramyxovirus from the dead horses — first called «equine morbillivirus», later renamed Hendra. But the real question is where the virus hides when it isn't killing horses and people. Vet-turned-ecologist Hume Field abandons his PhD on feral cats to hunt for this «reservoir host»: he bleeds rodents, reptiles and birds and finds no antibodies. Meanwhile, 900 kilometres north, cane farmer Mark Preston dies of encephalitis, and it emerges that he was infected a year earlier while helping nurse sick horses. Quammen builds the story so that the reader arrives at the answer — fruit bats — together with the researchers: the lone fig tree the first mare sheltered under was where the bats gathered.

Between the stories, Quammen explains the key ideas with great clarity. A zoonosis is an animal infection transmissible to humans; about 60% of known human infectious diseases fall into this category. Smallpox could be eradicated because it is not zoonotic, and polio is close for the same reason — the virus has nowhere to hide except in people. Zoonoses like yellow fever, Lyme or Ebola, however, can never be fully defeated because they hide in animal reservoirs. Simple, memorable lines such as «predators eat their prey from the outside, pathogens from the inside» are the book's great strength.

One of the most striking passages concerns «the Next Big One»: experts predict that the next great pandemic will be viral, will likely come out of a rainforest or a market in southern China, and will spread fast. Written in 2012, these lines are chilling to read after 2020. The closing part recalls Alan Berryman's provocative remark that, ecologically speaking, the greatest outbreak on the planet is Homo sapiens itself — more than seven billion people, roads cutting deeper into forests and markets create unprecedented opportunities for viruses to spill over.

Its weakness is its bulk: some sections stretch out with expedition detail, and the reader is loaded with names, labs and acronyms. Even so, among popular science books about pandemics it remains one of the most important and best written.

• A separate part for each pathogen — structured like a detective story
• The author's field trips and interviews with scientists
• Scientific concepts explained with everyday analogies