Human history, evolution and even our religious and cultural practices have been greatly influenced by plagues of infectious diseases. The Zika virus epidemic in South America has left a generation of children with microcephaly and raised concerns about infections acquired during large international gatherings such as the 2016 Olympic Games in Rio de Janeiro. The year 2014 will be remembered as the year that a highly contagious and deadly viral disease, Ebola, for the first time moved into large urban populations and quickly became a plague of high mortality and affliction. It directly affected three West African nations and their neighbouring countries, while threatening other nations around the globe. The 2014 Darwin College lecture series ‘Plagues’ had been conceived 18 months earlier, based not on a premonition of an Ebola epidemic, but on the inevitability of an outbreak of one of the many emerging and re-emerging infectious diseases from around the world. The ‘Plague’ lecture series and this book transcend the medical aspects of plagues by remaining true to the tradition of the multidisciplinary engagement of a single theme examining plagues of different types as well as those affecting other species in addition to humans. Plagues draws not only from the biological and medical sciences but also a spectrum of diverse fields such as those which infect our digital global network, threaten our financial institutions, and which have even influenced our language and literature. Intentionally, the sequence and the content of the chapters diverge from the platform lectures, which were limited in time and scope, thus now providing the reader with greater depth, detail and a broader conceptual perspective.

Due to an unfortunate coincidence, the ‘Plague’ lecture series was immediately followed by confirmation of the largest outbreak of one of humankind's most feared infections, Ebola. We have therefore most appropriately included a chapter ‘Ebola, the Plague of 2014/15’. This large-scale epidemic engulfed West Africa and threatened International borders. It took more lives than all other recorded Ebola outbreaks before it and dominated international headlines for two years. This contemporary plague began unrecognised with the death of a two-year-old boy in December 2013, a month before the Darwin College lecture series on plagues would start. Tragically, because Ebola was unknown to West Africa it was misdiagnosed until late March 2014.

Just over 200 years ago, there were fewer than a billion humans living on Earth. When I was born in 1960, there were three billion. In 2015, the human population has more than doubled to over seven billion people, and the UN projections expect that there will be ten billion humans on earth sometime towards the end of this century. This is if, optimistically, fertility rates continue to decline as they have done over the last fifty years. It is worth mentioning that this fifty-year decline in fertility rate, which many are keen to point out as a counter-claim to the argument that we have a problem, is actually slowing. It is also worth highlighting that if the current fertility rate were to continue unchanged (which the United Nations defines as the ‘constant fertility variant’), the global population at the end of this century would not be ten billion people, but will be twenty-eight billion.

With this in mind, I should point out that the UN population statistics have been systematically revised upwards over the past decade. The ‘peak’ population under the ‘expected scenario’ in 2100 was under ten billion. It is now over 11 billion according to estimates at the time of writing (Figure 8.1).

We associate plagues with epidemic diseases. The Darwin lecture series on Plagues was, by tragic serendipity, unwittingly launched on the eve of an erupting epidemic of humankind's most feared viral disease, Ebola. Little did we know that 2014 would be the start of the most serious single Ebola outbreak of our recorded history. It highlighted how plagues of such severe disease affect individuals in all layers of society, illustrating the frailty of human life with the unraveling of fragile health care systems, basic infrastructure, transportation and trade, leaving national economies on the brink of collapse.

Yet, the word ‘plagues’ has many more meanings. We explored these through the multidisciplinary approach used by the Darwin College Lecture Series, enriched by views of prominent scholars from very different fields. In this book the theme ‘plagues’ is portrayed not only by international experts of infectious diseases (vaccinology, biochemistry and medicine), but also from scholars in digital security, computational science, mathematical biology, ecology, genetics, history, economics, literature and theology. The result is a comprehensive spectrum of essays on plagues, from their impact on humanity to the animal kingdom, all bundled together in this one very unique book. It is another successful culmination of diverse perspectives on one such theme that the Darwin Lectures so uniquely weaves into one intellectually challenging topic.

Throughout history plagues have inflicted misery and suffering on humankind. Traces of these catastrophes are echoed in our literary past and, intriguingly, also encrypted and passed on through generations in our genes. Notably for the future of human population growth, the expansion of our species is challenging and changing the very environment we and other species require for survival on earth. We are also reminded that it may not just be the infectious plagues but also non-infectious ones that will impact this planet's species as this generation ages. The ever-expanding human population and our impact on climate threatens the delicate balance of ecosystems, making us a human plague to this fragile planet. Are plagues the manifestation of nature's checks and balances? This collection is a thought-provoking product of the topics of the 2014 Darwin College Lecture Series delivered by internationally renowned scholars, known not only for their outstanding work and literary talents, but for their ability to communicate the diverse facets and impacts of plagues.

How real is the risk of a digital Plague?

Very real.

We've already been fighting computer viruses and other types of malware for decades. They have evolved from simple, straightforward attacks to complicated, global outbreaks. In some ways, the evolution of online attacks resembles biological evolution. But the difference is that all computer attacks are created and launched by humans. By looking at examples of key malware attacks through the years, we can see how attacks on our digital world have evolved over time.

The Origins of Computer Viruses

Brain.A is considered to be the first PC virus in history. It was first detected in 1986. Several variants of the virus followed but most of them were fairly harmless. It ran on IBM-PCs and compatibles with PC-DOS operation systems. Brain was a boot sector virus, infecting the first sector of floppy discs as they were inserted into an infected computer. Brain was only a few kilobytes in size. Before Brain infected diskettes, it looked for a ‘signature’. This made it possible to ‘inoculate’ against the virus by putting the signature in the correct place of the boot sector of a clean floppy. Such floppies would not get infected even if they were inserted into an infected computer. The Brain virus tried to hide from detection by hooking the operating system functions that were used to read the floppy drive.

Most people associate the word ‘plague’ with the ‘Black Death’ of the mid-fourteenth century, which in the space of a few years killed between a third and a half of the population of Europe, Asia and the Middle East – with frightening consequences. However, throughout history there have been many other widespread and devastating outbreaks of disease that have been labelled as plagues. The word ‘plague’ comes from the Latin plaga, meaning a stroke or a wound; the Oxford English Dictionary also defines it as an affliction, calamity or a general name for any malignant diseases ‘with which men or beasts are stricken’. The word is, moreover, now becoming associated with some disorders that are not infectious, but which have increased in prevalence so rapidly that they have been likened to the historic plagues.

One such condition in humans is dementia, which has been called the ‘twenty-first century plague’, and indeed it is perhaps as greatly feared today as the classic plagues were in the past.

The 2014/2015 outbreak was the largest epidemic caused by a Filovirus such as Ebola, since Zaire ebolavirus was first identified in the 1970s. Having infected over 28,000 persons in West Africa it was slow to be recognised and contained. Unfortunately, resolving this epidemic was difficult and protracted, taking two years because of the unexpected appearance of late cases, some without links to someone with clinical disease. This created apprehension in the countries of Guinea, Sierra Leone and Liberia; nations which were economically and socially anxious that the epidemic was officially declared over.

This was a plague of modern times and revealed a number of unexpected outcomes. It changed paradigms not only in our understanding of this disease but also how new vaccines, medicines and diagnostic technologies could be fast-tracked, and changed how international responses to global infectious disease threats could be handled better in the future. This epidemic impacted on the small village communities as well as large urban centres. It changed practices and local perceptions of infectious diseases, re-established the critical importance of basic health infrastructure and highlighted the crippling impact that such gripping infectious diseases have on the struggling economies of developing countries.

Ebola: The Most Feared Contagion

In central Africa Ebola viruses are known to periodically strike remote villages, causing a terrifying haemorrhagic fever with high mortality. Unexpectedly in December 2013, at a distance of 3000 km west of the known heartland of Ebola in Central Africa, an outbreak of a mysterious disease began to spread, extracting a terrifying toll and killing many.

Infectious diseases, genomes and the arms race

The delicate balance between host species and their pathogens is akin to a deadly arms race, waged fiercely every day multiplied by individuals and populations in different geographical settings. These events are to a different extent recapitulated over the approximately 62,000 species of vertebrates that survive on earth today.

Scientific discoveries have changed the field of infectious diseases rapidly. New technologies constantly impact on the approaches that can be brought to bear on the problem. However, the study of the prevention of infectious diseases is not just about the biology underlying disease, but also about understanding society and individual behaviour. Ultimately, this is the conclusion I wish to deliver: the issues raised by our attempts to prevent plagues affect every member of society, not just the few fascinated by pathogens or our response to them.

Plagues’ Impact on Society

Most appropriately, the start of my analysis is 1347 and The Plague, known as the Black Death, that hit Europe. The historical details of The Plague are discussed in the preceding chapter ‘Plagues and History’ by Mary and Christopher Dobson. However, the importance of The Plague in Europe was that it was the first well-documented large-scale population pandemic. It affected everybody and spread to all parts of Europe, but leaving certain geographical pockets less affected than others.

To examine how to prevent the spread and impact of pathogens, it is important to consider the impact of The Plague on medieval society. Pieter Bruegel in his masterpiece The triumph of death (c.1562) depicts every conceivable grisly way of ending your life in medieval times. From scaffolds to being tortured on the wheel, a variety of ways of being decapitated or having other gruesome injuries inflicted on you are all there. But if this reflects the mind of medieval man, right in the centre is The Plague, with the characteristic plague cart filled with bodies.

So here is a perception of how plague affects individuals and in particular medieval man. Despite the fact that life was short and very hard by today's standards, the plague was perceived as a terrifying terminal event.

How did medieval man respond to this fearsome event? There were three possible options:

The first instinct, if you could afford it and the feudal system allowed it, was to run.

Any lecture series on plagues would need to ask how and why this happened, and when the Master and Fellows of Darwin College invited me to come back to Cambridge and suggest some answers, I jumped at the chance. Ernest Gellner's Darwin Lecture on the origins of society, delivered in the very first series (back in 1986), permanently changed the way I think about the past, and I could not possibly turn down this extraordinary honour. That said, the invitation was also intimidating, not least because the way I like to look at such big questions – through the lens of long-term history – has hardly been very prominent in previous Darwin Lectures. On reflection, however, that seemed to me all the more reason to accept.