published by W.W. Norton.

Ebola was the big disease story of 2014, but of course AIDS is still around. The AIDS pandemic has now killed about 39 million people worldwide and infected another 35 million. There’s little point in comparing these two public-health catastrophes, despite the obvious contrast in sheer magnitude, because each is so awful in its own way and each is so extraordinary. Yet they have at least one thing in common: They belong to a single category of phenomena—the category of rampaging zoonotic diseases.

A zoonotic disease, as I’ve explained elsewhere more than once, is a human affliction caused by an infectious bug (a virus, in each of these two cases) that has spilled over from nonhuman animals into humans.

Zoonotic diseases are the subject of my 2012 book Spillover—a work mainly devoted to the ecology and evolution of scary viruses—from which I extracted and reshaped sections to produce a little 2014 book, Ebola: The Natural and Human History of a Deadly Virus. I’ve now done the same thing (at the suggestion of W. W. Norton) with the long AIDS chapter from Spillover, in order to offer it too as a short, stand-alone book. The Chimp and the River: How AIDS Emerged from an African Forest is my answer to the jaded question, Why do zoonotic diseases really matter? The impetus in putting out Ebola was to offer a lean but substantial explanation of that virus—where it comes from and why and how it behaves—in the midst of an urgent situation. I thought of the book as an emergency information tool for news people, public officials, and anyone else concerned with the subject but too busy, or otherwise not likely, to read all 592 pages of Spillover. The impetus for releasing The Chimp and the River is different: AIDS has seemed urgent for 34 years now (since it was first recognized, in 1981), but most people still don’t comprehend how it took hold in humans, or when, or how, or why. The Chimp and the River explains that, and I have always seen this stretch of pages as a little self-contained book within a big one.

If you haven’t read Spillover, or followed certain discoveries in the arcane scientific journal literature of recent years, The Chimp and the River will give you a startlingly unexpected picture of the AIDS tragedy and its origins—a story of fateful accident, dark irony, and humanity’s bad luck that is very different from what you think you know.

For instance: The very beginning of AIDS has now been traced to a single event, localized rather precisely in place and time. The place was southeastern Cameroon, a small wedge of landscape in forested Central Africa from which two modest rivers (the Ngoko and the Sangha) drain toward the great freeway of brown water known as the Congo. The time was as early as 1908, give or take a margin of error. The event was an encounter—presumably a bloody encounter, a predator-prey interaction—between one human and one chimpanzee. The chimp happened to be carrying a blood-borne virus, which scientists much later have labeled SIV—an insidious thing, a retrovirus, slow-acting, with enormous potential to replicate, persist, and cause harm in the right host (meaning the wrong host, from our point of view), if it could blunder its way into such a promising situation. This virus passed from the chimp’s blood—through a cut on the man’s hand, maybe?—into the hunter’s bloodstream. SIV became HIV. (More precisely, the chimp’s version of SIV became the founder lineage of what’s now called HIV-1 group M, the pandemic strain. I explain all this in the book.) Forget about that Canadian airline steward, Gaetan Dugas, about whom you may have heard or read. The Cameroonian hunter, not Gaetan Dugas, was Patient Zero. From there, that single man, that moment, that mishap, the fateful strain of HIV spread through global humanity, like a bucket of blood flowing down a tile stairway.

The Chimp and the River tries to tell this story accurately, humanely, vividly, in the dimensions of history and ecology (and imagination), as the most dire and consequential of scientific detective tales. My years of reading and rereading the journals, the many interviews I conducted, my travels in remote places (including on the Ngoko River draining southeastern Cameroon, where I chartered a rickety pirogue to retrace the virus’s route) all went into this little book. For one stretch of the text, to connect the dots among known facts across gaps of unknowability, I created a sort of parable—that’s my hypothetical tale of the Cut Hunter and the Voyager—using the tools of a fiction writer (which I once was) to imagine the irrecoverable particulars of history.

Maybe that gambit works; maybe not. Something else I’ve said elsewhere: Safety is craft, when it comes to writing, and art entails risk. For whatever this may be worth, and I invite you to discount it as coming from the author: The Chimp and the River probably constitutes the riskiest and most important 176 pages I’ve ever written.



EBOLA: The Natural and Human History of a Deadly Virus



SPILLOVER: Animal Infections and the Next Human Pandemic



THE CHIMP AND THE RIVER: How AIDS Emerged from an African Forest