“The next pandemic will erupt, not from the jungle, but from the disease factories of hospitals, refugee camps and cities”
The latest epidemic to terrify the Western world is Ebola, a virus that has killed hundreds in Africa in 2014 alone. No wonder there was so much worry when two infected health care workers from the United States were transported home from Liberia for treatment – why bring this plague to the US, exposing the rest of the country as well? But the truth is that Ebola, murderous though it is, doesn’t have what it takes to produce a pandemic, a worldwide outbreak of infectious disease. It spreads only through intimate contact with infected body fluids; to avoid Ebola, just refrain from touching sweat, blood or the bodies of the sick or dead.
Yet no logic can quell our pandemic paranoia, which first infected the zeitgeist with the publication of Laurie Garrett’s The Coming Plague (1994) and Richard Preston’s Hot Zone (1995). These books suggested that human incursion into rainforests and jungles would stir deadly viruses in wait; perturb nature and she nails you in the end. By the late 1990s, we were deep into the biological weapons scare, pumping billions of dollars in worldwide government funding to fight evil, lab-made disease. As if this weren’t enough, the panic caused from 2004 to 2007 by reports of the H5N1 or bird flu virus etched the prospect of a cross-species Andromeda strain in the Western mind.
The fear seems confirmed by historical memory: after all, plagues have killed a lot of people, and deadly diseases litter history like black confetti. The Antonine Plague, attributed to measles or smallpox in the year 165 CE, killed the Roman Emperor Marcus Aurelius and millions of his subjects. The Justinian Plague, caused by the deadly bacterial pathogen Yersinia pestis, spread from North Africa across the Mediterranean Sea to Constantinople and other cities along the Mediterranean. By 542, infected rats and fleas had carried the infection as far north as Rennes in France and into the heart of Germany. Millions died.
Then there was the Black Death of 1348-50, also caused by Yersinia pestis, but this time spread by human fleas and from human lung to human lung, through the air. The plague spread along the Silk Road to what is now Afghanistan, India, Persia, Constantinople, and thence across the Mediterranean to Italy and the rest of Europe, killing tens of millions worldwide. Of all the past pandemics, the 1918 influenza (also known as the Spanish flu) is now considered the über-threat, the rod by which all other pandemics are measured. It killed 40 million people around the globe.
It was the great Australian virologist Frank Macfarlane Burnet who argued that the deadliest diseases were those newly introduced into the human species. It seemed to make sense: the parasite that kills its host is a dead parasite since, without the host, the germ has no way to survive and spread. According to this argument, new germs that erupt into our species will be potential triggers for pandemics, while germs that have a long history in a host species will have evolved to be relatively benign.
Many health experts take the notion further, contending that any coming plague will come from human intrusion into the natural world. One risk, they suggest, comes when hungry people in Africa and elsewhere forge deep into forests and jungles to hunt ‘bushmeat’ – rodents, rabbits, monkeys, apes – with exposure to dangerous pathogens the unhappy result. Those pathogens move silently among wild animals, but can also explode with terrifying ferocity among people when humans venture where they shouldn’t. According to the same line of thought, another proposed risk would result when birds spread a new pandemic strain to chickens in factory farms and, ultimately, to us.
But there’s something in these scenarios that’s not entirely logical. There is nothing new in the intimate contact between animals and people. Our hominid ancestors lived on wildlife before we ever evolved into Homo sapiens: that’s why anthropologists call them hunter-gatherers, a term that still applies to some modern peoples, including bushmeat hunters in West Africa. After domesticating animals, we lived close beside them, keeping cows, pigs and chickens in farmyards and even within households for thousands of years. Pandemics arise out of more than mere contact between human beings and animals: from an evolutionary point of view, there is a missing step between animal pathogen and human pandemic that’s been almost completely overlooked in these terrifying but entirely speculative ideas.
According to the evolutionary epidemiologist Paul W Ewald of the University of Louisville, the most dangerous infectious diseases are almost always not animal diseases freshly broken into the human species, but diseases adapted to humanity over time: smallpox, malaria, tuberculosis, leprosy, typhus, yellow fever, polio. In order to adapt to the human species, a germ needs to cycle among people – from person to person to person. In each iteration, the strains best adapted to transmission will be the ones that spread. So natural selection will push circulating strains towards more and more effective transmission, and therefore towards increasing adaptation to human hosts. This process necessarily takes place among people.
posted by f.sheikh