The Chimp and the River: How AIDS Emerged from an African Forest
By David Quammen
New York: W.W. Norton, 174 pp,
ISBN: 978-0-393-35084-5, 2015. $13.95 (USA), paperback
William C. McGrew
Division of Biological Anthropology,
Dept. of Archaeology and Anthropology,
University of Cambridge, UK
Most of us who study chimpanzees probably will pick up a book that has our subject species in its title, out of curiosity. (Even if the demeaning abbreviation, “chimp”, is used!) I did so in a Borders bookshop, having never heard of this book before then. I HAD heard of its predecessor, Spillover. Animal Infections and the Next Human Pandemic, by the same author, published in 2012. As it turns out, Quammen extracted a chapter from the first book and then adapted it for publication as another book on its own.
Quammen is an award-winning science writer, probably best known for an earlier book, The Song of the Dodo. He has written before about non-human primates, notably for National Geographic, about Gombe and Jane Goodall, but in this book, he travels to central Africa to seek first-hand information about his topic. In a nutshell, the chimpanzee in the title is the hypothetical individual Pan t. troglodytes who passed on to a hunter the virus that became HIV-1. The river is the Sangha River, the hypothetical avenue down which the virus travelled to reach Brazzaville and Leopoldville (now Kinshasha), from whence it spread out to infect the globe.
Quammen makes clear his aim in the introduction: To trace backward from the current pandemic of HIV-AIDS to its origin, then to follow its progress via history, epidemiology and accident to its “spillover.” Thus, according to him, it is a saga with three main characters: chimpanzee, human and virus. This attempt at reconstruction is a real challenge, for by the time HIV-AIDS was identified, its origins were lost in the past, to be elucidated only by retrospective inference, from limited, piece-meal, and non-random evidence. His thesis is simple: Just over a century ago, a single SIV-infected chimpanzee was killed or butchered by a single African hunter from southeastern Cameroon. That event of zoonoses (transmission from animal to human) was the trigger, from whence all else proceeded.
Technically, the book is admirable. It is written in elegant and intelligible English, all lean and no fat. It has 25 chapters, short and punchy, often with cliff-hanging final sentences, to keep the reader moving on. The good news is that there are 139 endnotes that allow the reader to follow up any point, and there are about 100 references in which to do so. The 10-page index is detailed and useful. The less-good news is that there are no illustrations, not even a map of the key places of the journeys made by the virus, or the author.
The argument is by plausibility, based on the first recovered evidence of the virus (dating back to 1908), then on later medical evidence collected sporadically and serendipitously in the ensuing decades, until modern studies, principally by Beatrice Hahn and colleagues, have sought and obtained new data, in proactive, hypothesis-testing mode. These latter field studies have utilised non-invasive methods, by extracting antibodies from urine or virus fractions from faeces, thus allowing cooperation with ongoing projects done by field primatologists. However, the timing of the key events can be inferred only by the molecular clock, via comparison of variants in nucleotide substitutions, as no actual chronology is possible.
So, what are its limits? First, it is out of date. Basically it is the story up to Keele et al. (2009), which revealed that wild chimpanzees do suffer from their own version of AIDS. Second, as presented here, the evidence from wild chimpanzees comes only from Gombe, which is notable, given that P. t. t. in Cameroon is a different subspecies from P. t. schweinfurthii in Tanzania. Since then, SIVcpz has been found in other populations of P. t. s. and P. t. t. (Rudicell et al. 2011) but not (yet) in P. t. v. (Leendertz et al. 2011). Third, Quammen is clearly committed to a narrative (Cut Hunter Hypothesis), to which the evidence is made to fit. To give a simple example, the possibility of human to animal transmission (anthroponoses?) as an alternative explanation is never mentioned. Presumably this is ruled out because SIV is said to be older and more diverse than HIV (to put it simplistically). Certainly, humans preying on apes is more common than apes preying on humans, but the latter does occur (Frodo’s consumption at Gombe of a human infant, while its mother and others could only watch in horror, being a graphic example). And, it turns out that SIVcpz may be no more varied that HIV-1, M lineage, with its nine subtypes. So, perhaps it is not so clear who infected whom?
So, why should a chimpologist read this book? First, field primatologists (e.g., Jane Goodall, Richard Wrangham) play prominent roles in the story. Second, it provides a succinct and readable account of the SIV-HIV origins story, to which students and others can be referred for background reading. Thus, it offers a basis for answering testing questions about the relationship between chimpanzees and HIV-AIDS. Third, on a completely different level, it reminds us that physical contact with both human and chimpanzee blood is a risky business, wherever and however it may occur.
Keele BF, Jones JH, Terio KA et al. 2009. Increased mortality and AIDS-like immunopathology in wild chimpanzees infected with SIVcpz. Nature 469:515–519.
Leendertz SAJ, Locatelli S, Boesch C et al. 2011. No evidence for transmission of SIVwrc from western red colobus monkeys (Piliocolobus badius badius) to wild West African chimpanzees (Pan troglodytes verus) despite high exposure through hunting. BMC Microbiol 11:24.
Rudicell RS, Piel AK, Stewart F et al. 2011. High prevalence of simian immunodeficiency virus infection in a community of savanna chimpanzees. J Virol 85:9918–9928.
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