Spillover: Animal Infections and the Next Human Pandemic by David Quammen
| Spillover: Animal Infections and the Next Human Pandemic by David Quammen | |
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| Category: Popular Science | |
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Reviewer: Gloria Nneoma Onwuneme
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| Summary: On the impact which zoonoses have had, continue to have, and may have on human beings. | |
| Buy? Maybe | Borrow? Yes |
| Pages: 592 | Date: August 2013 |
| Publisher: Vintage | |
| ISBN: 978-0099522850 | |
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We provide an irresistible opportunity for enterprising microbes by the ubiquity and abundance of our human bodies. This is a salient fact taken away from David Quammen’s Spillover. The entire book is a most trenchant eye-opener to just how much of an impact animal infections have on people; approximately 60% of human infectious diseases are zoonoses, 'animal [infections] transmissible to humans'.
The stories of how the outbreaks of these zoonoses happen are told, all saying something about what determines the level of the detrimental effects they have on people. Historically, rather dramatic events have preceded the discoveries of the pathogens responsible. The book starts with the mysterious deaths of horses, horse trainers and cane farmers in the Australian town Hendra, caused by what was found to be a new virus. The 1996 deaths of 18 people who died after eating a chimp cadaver in Mayibout 2, Gabon, was in fact a case announcing the re-emergence of Ebola in six different central African countries. In more recent times, SARS entered the limelight for a while, when a 78 yr old woman flew from Hong Kong to Toronto, taking a stealthily spreading endemic global. Possibly more disconcerting than all of these is the story of what might be the universally scariest pathogen, HIV, with stronger and stronger links being established between SIV and the currently dominant Next Big One in the lineage of transmissible diseases.
The list of zoonoses is a long one, caused by six main kinds of microbes (or in the case of viruses, protein coats containing genetic material). It features all influenzas, psittacosis (or parrot fever), Q fever, rabies, Lyme disease, Nipah virus, and many more. But regardless of all the measures taken against these, including a US embargo against the import of parrots, and the culling of pigs and deer, zoonoses remain that much more of a challenge for various reasons. Besides the obvious difficulty that the extermination of whole species presents, there’s the complexity of the systems by which pathogens actually spill over from (other) animals to human beings. For one, the reservoir hosts are often misidentified. The deer associated with Lyme disease actually turned out to merely be a comfortable habitat for ticks which bore the bacterium responsible. And their fur wasn’t even greatly preferred by the ticks in comparison to those of rodents. The massacre of 1.1m pigs in Malaysia, the ewes with Q fever who miscarried extensively in the Netherlands and the sickly equines in Australia all have bats to blame for the Nipah virus, Coxiella burnetii and Hendra virus they were given, respectively. The strangely expansive role chiropterans seem to play in the sudden outbreaks of zoonoses isn’t so strange, given that they make up about 20-25% of all classified mammalian species.
Another issue is the fact that one is able to conclude that mankind is increasingly presenting itself as a host to opportunistic pathogens, by seeking to seize all this planet has to offer. We continually encroach upon nature and the rapid progress of technology is making our world smaller and smaller. Sir Frank McFarlane Burnet, who identified the agents of Q fever and psittacosis, was completely right to urge the medical field to consider the ecological context in which we find, or place, ourselves, when it comes to infectious diseases.
The field of infectious disease pathology is heeding this advice more and more, and Quammen gives accounts of his experiences with science investigators, scattered far and wide, posing all sorts of questions. Why do some zoonoses succeed more than others in taking a hold on people? What factors impact success of infiltration of Homo sapiens sapiens? Sometimes the answer to this lies in the way in which man acts upon nature; it was observed that shortly before the SARS coronavirus explosion, the trend of Eating Wild (by exploring exotic sources of meat) exploded in Southeast-Asia, for the trade in game to have gone hidden after SARS smouldered.
The question of zoonoses has engendered quite a few developments, including the 'mathematizing' of disease dynamics, and the scrutiny of just what factors into the profligation of a zoonosis. Some researchers have suffered fatal accidents in biohazard level 4 laboratories, inadvertently giving themselves herpes B and Ebola. Others come away unscathed, though constantly having to conduct field research in caves heavily populated by bats who are probably infected with the virus they seek to extract or cultivate. Others still pursue viruses by taking insanely long walks in unwelcoming terrains, frantically looking for traces of infected rodents, all in the name of finding some answers.
Just how distinct is a zoonosis from a non-zoonosis? The exploration of this question which I find most fascinating is that of HIV; molecular phylogeny generally shows that if one goes far back enough, what may affect only one species today might actually have made the leap from one animal to another further back in time. The human immunodeficiency virus – which was first written about in Morbidity and Mortality Weekly Report, then went through a series of name changes – is being shown to have more definitive roots in SIV, the equivalent which affects other primates. The widely circulated Cut-Hunter explanation (in which it is supposed that a hunter somewhere in Central Africa killed an infected chimpanzee, and may have cut himself) represents a small part of the story, according to some. The observed twelve subtypes of HIV even suggest to some that there were at least twelve spillovers of HIV into human beings!
What drives an endemic to cross the Rubicon and go global? The question is partially answered by Quammen, who states that two crises promote the growth of zoonoses: The first crisis is ecological, the second is medical. The extensive globalisation, the inimical invasion of nature (by means of measures such as deforestation, or increased hunting for game) and the slight blind spot humans suffer from, when it comes to just how interconnected various forms of life is, can lead to some rather disastrous consequences. How might this be prevented? That is still rather unclear, I’m afraid.
Stretching into the past, and reaching into the future, Quammen has done a splendid job at illuminating the tale of zoonoses and writing of the animals, unsuspecting societies and tenacious researchers involved. It points to the possibility that a zoonosis would be included in the chain of the Next Big Ones, succeeding the bubonic plague, smallpox, 1918-1919 influenza pandemic, and HIV/AIDS. More importantly, while Quammen doesn’t state that we humans are exclusively responsible for the crossing over of animal diseases, one is as a reader reminded yet again of just how unisolated we are from nature.
A lot of zoonotic agents start out as large question marks in the realm of science. For more on how similar medical enigmas are unpacked, have a read of Diagnosis: Dispatches from the Frontlines of Medical Mysteries by Lisa Sanders.
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You can read more book reviews or buy Spillover: Animal Infections and the Next Human Pandemic by David Quammen at Amazon.com.
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