Spillover: Animal Infections and The Next Human Pandemic by David Quammen (W. W. Norton & Company 2013. Published in the UK by Penguin)
David Quammen – well known nature essayist and author of popular science books on topics ranging from epidemics to evolution - takes us on a quest to trace the sources of recent virus outbreaks.
As we have previously noted in the Encyclopaedia Pandemica posts, Covid-19 has caused the viral spread of a particular phenomenon: all manner of publishers, news & media organisations and even scientific journals have been compiling lists of the best books about pandemics. These range from serious literature to bestseller, from academic textbooks to popular science writing. In some cases, they include books about, say, isolation or self-help manuals to aid us as we navigate the lockdown.
Within this is a tendency to re-visit any book that seemed to predict a “next pandemic”, declare the author as prescient, and if possible interview them about the prophecies they made all those years ago. How did they know there was going to be another outbreak? what led them to predict the government was going to have to do something about it? Obvious questions, perhaps, from a Western European or North American perspective where we have not had to do this before.
The point generally overlooked is that there is always going to be a “next pandemic”. There will always have to be control measures and governments will always have to balance human against economic costs. The difference here is the direct relevance to Covid-19; the title “Spillover” refers to the “spilling over” or transmission of viruses and other pathogenic microbes from animal to human populations. Infections which do this are called zoonoses.
We are familiar with the idea of illnesses such as Bubonic Plague, Malaria, Rabies, BSE and Avian ‘flu being transmitted from animals to humans. We may be less familiar, however with the zoonotic nature of infections such as HIV, SARS and Ebola. Quammen spent five years tracking down the origins of these and other viruses – traveling extensively, interviewing leading scientists, field workers and those affected by the infections. The result is a highly readable and gripping account – a proverbial page-turner - combining journalism, science, history and travel with tension, tragedy and humour thrown in for good measure, plus a sprinkling of pithy character sketches and anecdotes.
Sobering if not scary is the thought of what the viruses are up to between outbreaks. Not everyone will be familiar with the idea that groups of wild animals must constantly carry the infection. Taking Ebola as an example, there must be a “reservoir” species, which has been carrying the virus for many years and so must be adapted to it – in other words it is endemic rather than epidemic. Every so often the virus spills over, perhaps via intermediate hosts in which the virus become pathogenic, then on to infect primates – humans, gorillas chimpanzees – resulting in punctuated localised outbreaks. The wave-like spread of Ebola across Central Africa from 1976 onwards demonstrates this. Extrapolating from 2012 when Spillover was published, the spread of the disease can be followed into West Africa (Guinea, Liberia, Sierra Leone) where the largest outbreak so far occurred in 2014. Fortunately, the outbreaks of Ebola have remained at a fairly local level – the epidemic has not become a pandemic. And so far, the reservoir species for Ebola has not been identified.
As we are aware, the current coronavirus is said to have originated from bats in a Chinese “wet market”, so called because the produce is kept cool by spraying it with water. These markets sell a wide variety of fresh goods and live wild animals such as birds, snakes and bats intended for the local cuisine. Bats have been implicated as hosts in previous spillovers to humans, but while research has shown that coronaviruses can be transmitted directly from bats to humans it is usually through an intermediate species such as civet cats (SARS) or camels (MERS). With Covid-19, the current focus is on pangolins. As is the case with Ebola, we may never find out the true details of the transmission chain.
Back in 2012, Quammen predicted “The next big and murderous human pandemic ... will be caused by a new disease—new to humans, anyway. The bug that’s responsible will be strange, unfamiliar, but it won’t come from outer space. Odds are that the killer pathogen—most likely a virus—will spill over into humans from a nonhuman animal.” While that may seem uncannily accurate given the current Covid-19 situation, Spillover tells us that this has been the case for the majority of epidemics and pandemics from the 1970s onwards. So why the increased frequency of zoonoses? Are our detection methods are just better nowadays, or is it something we’re doing wrong that’s causing this?
Whatever the answer, the one certainty is that there is always going to be a next pandemic and it is likely to be zoonotic.