Spillover: Animal Infections and the Next Human Pandemic

I have seen the spillover, and it is us. ( )

An excellent foray through old & new zoonosis, & the factors influencing their transmission, both human & non human. Genuinely frightening, but also insightful. Recommended for those with an interest in the subject & some technical knowledge. ( )

A fascinating, riveting, and terrifying look at zoonotic viruses. It seems likely that the next pandemic will result from our ongoing destruction of rainforest habitats. I've also decided that if I ever do have the opportunity to visit China I'm going to bring my own food. ( )

Zoonosis: any infection or disease that is transmitted to man from lower vertebrates
Spillover: that time point where the disease, which may have evolved through millennia with its animal host, comes in contact and establishes itself itself in a new host, including humans.

This is a brilliant book of medical detection of past and present infectious disease events and predictions of ‘the next big one’. Quammen is careful not to oversensationalize the story he methodically lays out his conclusions in this 500 page book.

Quammen begins by recounting a recent zoonotic spillover event—the outbreak of Hendra virus in Australia that killed race horses and the people that work with them. He outlines the epidemiological detective work in determining the virus, its natural animal reservoir and the mode of transmission into racehorses. He speculates why the virus made the jump at this particular time.

And then he does it again with dozens more infectious outbreaks, each a puzzle of its own. Some of these are frightening with high death rates and sensational headlines: Ebola, SARS, Influenza, AIDS and the not quite as deadly Lyme disease. Others are less well known but are also killers : Q fever, psittacosis, typhus and even the vector borne malaria.

Each infection has an interesting story to tell by itself. Each one adds to the store of knowledge and we find the patterns and make predictions from the patterns:

-The next epidemic is liable to occur from a virus with RNA as its genome rather than DNA due to RNA's high rate of mutation and evolution.

-A human to human disease with no animal reservoir can be eliminated from the planet (smallpox)—but one that lurks within an animal host cannot be eradicated without eliminating all the members of the natural animal host species.

-The deadly influenza outbreak of 1918 is liable to happen again as influenza has two host species (birds and swine) whose specifically evolved influenza viruses can recombine within a single host into deadly new combinations.

--AIDS/HIV most probably entered humans from a single spillover event from an infected ape in 1908. It sputtered along hidden in humans in the jungles of Africa until certain events made it explode into worldwide prevalence in the 1970’s. It has currently caused tens of millions of deaths. Are the small flares of Ebola evidence that it is following the same path?

Finally, Quammen gives the example of tent caterpillars whose numbers increase dramatically every few years. Then, when their population reaches a certain density, caterpillar numbers plummet dramatically when a caterpillar-killing virus wipes out almost-but-not-quite all of their population. When the caterpillar numbers become low enough to contain viral spread, the virus declines and the population of caterpillars can once more begins to rise.

Finally, Quammen turns our attention to the ubiquity of the human race and their exponential growth rate. As human populations become more crowded and also more mobile, the potential for disease spread increases greatly. In addition we are disturbing more and more animal habitat with our increased numbers, more frequently putting us in the path for spillover events to occur. Is there any way to avoid the caterpillar’s fate? ( )

In Spillover, David Quammen provides us with yet another of his masterful books, combining a readable synthesis of scientific research with personal interviews, experiences, and ruminations. This time it's not on natural selection or island biogeography, but on zoonotic diseases (illnesses which pass from animals to humans). From Marburg to AIDS to Hendra virus and Nipah, Quammen explains how scientists think these diseases come to the spillover point (when the pathogen passes from one species to another) and explores the consequences.

The book is absolutely terrifying, even though Quammen takes pains not to oversensationalize his subject (in fact he takes exception to Richard Preston's having done just that in The Hot Zone). It's simply the facts of the case as Quammen lays them out: these diseases are nasty, they're lurking, and sooner or later, one of them is very likely to cause "the next human pandemic." Since I don't follow the professional virological literature, I was astounded to learn about the role of bats (particularly large Asian fruit bats) as reservoir hosts of these nasty bugs; Quammen devotes much attention to this, to great effect.

While Spillover gets just a touch repetitive over the course of the book (the text of which runs to 520 pages), I didn't actually mind all that much, since the repeated bits generally proved a useful refresher. This is a book which I hope will have a large audience: as Quammen notes, humanity is anything but a passive actor when it comes to disease evolution and spread: our actions over the last centuries and decades have laid the groundwork for much of what may come, and we are, whether we like it or not, completely entangled in the ecological processes of our planet.

Terrifying, yes, but read it. You'll learn something. ( )