SPILLOVER is a fascinating and in-depth exploration of zoonoses – i.e. diseases that can jump from various animal species into humans. This continues to be a germane topic in the face of our current zoonotic pandemic – COVID-19. The book came out in 2012 / 2013, but has seen a groundswell of interest because it’s the most well-known popular work on this subject. One will read a few sentences in the book that seem prescient, but the author and the many experts he consults would be the first to state that this is no act of mystical precognition. Rather, a zoonotic pandemic seems to be an inevitability given humanity’s huge and growing population and the nature of our interactions with the rest of the animal kingdom. Of course, no one could say precisely when or what pathogen would lead to “the next big one,” of which – it so happens – we are currently amid. Though coronaviruses do come up as potential candidates, but so do others (e.g. certain strains of influenza.)
The book is organized differently than most. It’s cut up into bite sized chunks, with 115 chapters that are usually not more than a few pages each. However, chapters aren’t the relevant unit of interest so much as the book’s nine parts, each of which takes on a particular zoonosis, or class thereof. Because zoonoses are such a huge topic, the author focuses on a few that are of particular interest for varied reasons, including: the challenge of tracking the disease’s origins, the potential to be the next big one, the global influence of some diseases, as well as other reasons a particular zoonosis generates an interesting story.
The first part explores one of the lesser known zoonoses (except for in locales where outbreaks have occurred, e.g. Australia,) Hendra virus. While a common species of bat (the flying fox) is the reservoir for Hendra, what makes the story gripping for humans is that humans contract the disease through the intermediary of horses. While interaction with exotic wildlife is the the mode throughout the book, the fact that, here, transmission occurs from one of humanity’s closest animal friends increases the closeness-to-home effect.
Part two shifts into one of the most dramatic and well-known of the zoonoses, Ebola virus. Ebola is familiar from Richard Preston’s book “Hot Zone,” though Quammen does explain how Preston sensationalized and overstated the physical effects of the disease. [Presumably what Preston did was take the most vicious looking case and describe it through as dramatic of analogies as possible, such that it became unrecognizable from the typical case.] At any rate, it’s a disease that grabs one by the fear center because – while it doesn’t spread readily – it’s highly lethal and is unarguably an unpleasant way to go.
Part three delves into malaria and P. falciparum, the bug that causes it. Malaria has profoundly shaped human existence in the tropics. A vector-borne disease carried and passed by mosquitos, Malaria is widespread throughout much of the world and continues to generate debilitating effects. Many concepts are drilled into one while reading this book, and one worth mentioning here is the differentiation of reservoirs and vectors. A lot of the stories in this book revolve around scientists’ searches for reservoirs – the species where the pathogen resides in waiting. It’s often much more difficult to uncover a reservoir species than it is a vector (vectors invariably coming into direct contact with humans, whereas reservoirs can be far removed from humans.)
Part four investigates Severe Acute Respiratory Syndrome (SARS.) This is one of the most relevant sections because SARS is a corona virus — like COVID-19 — and it served as a harbinger of a corona virus pandemic. SARS is also at least vaguely familiar to most people as it was a relatively recent epidemic.
The next two sections zoom out a bit and, instead of diving down into one zoonosis, they each consider a range of bacterial and viral zoonoses, respectively. Part five discusses Q fever, Lyme disease, Psittacosis, and other bacterial diseases that enter humans by way of other animals. Part six explores a range of viral diseases and – in the process – gives a bit of a lesson as to why viruses present such a risk as well as how different viruses work. This section covers rabies and Nipah virus.
Part seven tells the story of the search for the Marburg virus origin and reservoir. Marburg is similar to Ebola, but the story of the epidemiological search for it makes for intriguing reading. Part eight discusses HIV-AIDS and its simian predecessor, SIDS. What made this fascinating to me was that I learned that HIV has been around (at least) since the first decade of the twentieth century. If you’re like me, you associate the origin of AIDS with the 1980’s. However, with so many people regularly dying from so many different conditions in central Africa, it wasn’t obvious that those killers were getting an added help from a virus that crippled immune systems. It also took scientist a while to realize that SIDS was resulting in the death of chimpanzees. (It’s possible for a reservoir to be unaffected by a disease, and this is what they first thought to be the case.)
The final part is a wrap up that zooms out to look at the nature of episodes of ecological imbalance and “outbreaks” of species. In this case, “outbreak” is used to describe any explosion of population growth of a species. While the section opens with a species of caterpillars [forest tent caterpillars] that would occasionally flare up, killing off trees on a large scale, it discusses human population growth as an outbreak that – like all others – will inevitably end one way or another. This section also discusses influenza (which isn’t a major topic earlier in the book,) presumably because it had been the lead candidate at the time for the “next big one.” And “the next big one” is a related overarching theme in this section.
The book is annotated and has an extensive bibliography. There are few graphics, but there are maps that are helpful for those who aren’t familiar with the areas where many of these disease outbreaks originated (e.g. central Africa.)
I found this book to be intriguing. It teaches the reader some basics of epidemiology as it goes about telling the story of the spread of these diseases. [e.g. It will help one distinguish virulence and transmissibility – terms that are often used by neophytes interchangeably, but which are distinct in important ways.] However, the focus is always on the story and, therefore, it keeps these lessons interesting throughout. I’d highly recommend this book for those who are interested in the pandemic, zoonoses, or the challenges of combating disease.