The social history of viruses describes the influence of viruses and viral infections on human history. Epidemics caused by viruses began when human behaviour changed during the Neolithic period, around 12,000 years ago, when humans developed more densely populated agricultural communities. This allowed viruses to spread rapidly and subsequently to become endemic. Viruses of plants and livestock also increased, and as humans became dependent on agriculture and farming, diseases such as potyviruses of potatoes and rinderpest of cattle had devastating consequences.
Smallpox and measles viruses are among the oldest that infect humans. Having evolved from viruses that infected other animals, they first appeared in humans in Europe and North Africa thousands of years ago. The viruses were later carried to the New World by Europeans during the time of the Spanish Conquests, but the indigenous people had no natural resistance to the viruses and millions of them died during epidemics. Influenza pandemics have been recorded since 1580, and they have occurred with increasing frequency in subsequent centuries. The pandemic of 1918–19, in which 40–50 million died in less than a year, was one of the most devastating in history.
Louis Pasteur and Edward Jenner were the first to develop vaccines to protect against viral infections. The nature of viruses remained unknown until the invention of the electron microscope in the 1930s, when the science of virology gained momentum. In the 20th century many diseases both old and new were found to be caused by viruses. There were epidemics of poliomyelitis that were only controlled following the development of a vaccine in the 1950s. HIV is one of the most pathogenic new viruses to have emerged in centuries. Although scientific interest in them arose because of the diseases they cause, most viruses are beneficial. Retroviruses drive evolution by transferring genes across species and bacteriophages play important roles in ecosystems and are essential to life.
In prehistory Over the past 50,000–100,000 years, as modern humans increased in numbers and dispersed throughout the world, new infectious diseases emerged, including those caused by viruses. Earlier, humans lived in small, isolated communities, and most epidemic diseases did not exist.Clark, p. 56Barrett and Armelagos, p. 28 Smallpox, which is the most lethal and devastating viral infection in history, first emerged among agricultural communities in India about 11,000 years ago.Villarreal, p. 344 The virus, which only infected humans, probably descended from the poxviruses of rodents. Humans probably came into contact with these rodents, and some people became infected by the viruses they carried.
When viruses cross this so-called "species barrier", their effects can be severe, and humans may have had little natural resistance. Contemporary humans lived in small communities, and those who succumbed to infection either died or developed immunity. This acquired immunity is only passed down to offspring temporarily, by antibodies in breast milk and other antibodies that cross the placenta from the mother's blood to the unborn child's. Therefore, sporadic outbreaks probably occurred in each generation. In about 9000 BC, when many people began to settle on the fertile flood plains of the River Nile, the population became dense enough for the virus to maintain a constant presence because of the high concentration of susceptible people.Tucker, p. 6 Other epidemics of viral diseases that depend on large concentrations of people, such as mumps, rubella and polio, also first occurred at this time.Clark, p. 20
The Neolithic age, which began in the Middle East in about 9500 BC, was a time when humans became farmers.Barker, p. 1 This agricultural revolution embraced the development of monoculture and presented an opportunity for the rapid spread of several species of plant viruses. The divergence and spread of sobemoviruses – southern bean mosaic virus – date from this time. The spread of the potyviruses of potatoes, and other fruits and vegetables, began about 6,600 years ago.
About 10,000 years ago the humans who inhabited the lands around the Mediterranean basin began to domesticate wild animals. Pigs, cattle, goats, sheep, horses, camels, cats and dogs were all kept and bred in captivity. These animals would have brought their viruses with them.McNeill, p. 71 The transmission of viruses from animals to humans can occur, but such zoonotic infections are rare and subsequent human-to-human transmission of animal viruses is even rarer, although there are notable exceptions such as influenza. Most viruses are species-specific and would have posed no threat to humans.Baker, pp. 40–50 The rare epidemics of viral diseases originating in animals would have been short-lived because the viruses were not fully adapted to humansMcNeill, p. 73 and the human populations were too small to maintain the chains of infection.Clark, p. 57–58
Other, more ancient, viruses have been less of a threat. Herpes viruses first infected the ancestors of modern humans over 80 million years ago.Crawford (2000), p. 225 Humans have developed a tolerance to these viruses, and most are infected with at least one species. Records of these milder virus infections are rare, but it is likely that early hominids suffered from colds, influenza and diarrhoea caused by viruses just as humans do today. More recently evolved viruses cause epidemics and pandemics – and it is these that history records.
In antiquity
Among the earliest records of a viral infection is an Egyptian stele thought to depict an Egyptian priest from the 18th Dynasty (1580–1350 BC) with a foot drop deformity characteristic of a poliovirus infection.Shors, p. 16 The mummy of Siptah – a ruler during the 19th Dynasty – shows signs of poliomyelitis, and that of Ramesses V and some other Egyptian mummies buried over 3,000 years ago show evidence of smallpox.Donadoni, p. 292Taylor, p. 4 There was an epidemic of probable smallpox in Athens in 430 BC, in which a quarter of the Athenian army and many of the city's civilians died from the infection. The Antonine Plague of 165–180 CE, another probable smallpox pandemic, wiped out around five million people in the Roman Empire, which included Britain, Europe, the Middle East and North Africa.Baker p. 25 The pandemic began after Roman soldiers who were sent to suppress an uprising in what is now Iraq, plundered the city of Seleucia on the river Tigris and at the same time were infected. They brought the disease back to Rome and Europe where up to 5,000 people a day were fatally infected. At its height, the pandemic reached India and China.Crawford p. 78
Measles is an old disease, but it was not until the 10th century that the Persian physician Muhammad ibn Zakariya al-Razi (865–925) – known as "Rhazes" – first identified it.Levins, pp. 297–298 Rhazes used the Arabic name hasbah (حصبة) for measles. It has had many other names including rubeola from the Latin word rubeus, "red", and morbilli, "small plague".Dobson, pp. 140–141 The close similarities between measles virus, canine distemper virus and rinderpest virus have given rise to speculation that measles was first transmitted to humans from domesticated dogs or cattle.Karlen, p. 57 The measles virus appears to have fully diverged from the then-widespread rinderpest virus by the 12th century.
A measles infection confers lifelong immunity. Therefore, the virus requires a high population density to become endemic, and this probably did not occur in the Neolithic age. Following the emergence of the virus in the Middle East, it reached India by 2500 BC. Measles was so common in children at the time that it was not recognised as a disease. In Egyptian hieroglyphs it was described as a normal stage of human development. One of the earliest descriptions of a virus-infected plant can be found in a poem written by the Japanese Empress Kōken (718–770), in which she describes a plant in summer with yellowing leaves. The plant, later identified as Eupatorium lindleyanum, is often infected with tomato yellow leaf curl virus.Mahy, (a) p. 10
Middle Ages
The rapidly growing population of Europe and the rising concentrations of people in its towns and cities became a fertile ground for many infectious and contagious diseases, of which the Black Death – a bacterial infection – is probably the most notorious. Except for smallpox and influenza, documented outbreaks of infections now known to be caused by viruses were rare. Rabies, a disease that had been recognised for over 4,000 years,Mahy, (b) p. 243 was rife in Europe, and continued to be so until the development of a vaccine by Louis Pasteur in 1886.Shors, p. 586 The average life expectancy in Europe during the Middle Ages was 35 years; 60% of children died before the age of 16, many of them during their first 6 years of life. Physicians – what few there were – relied as much on astrology as they did on their limited medical knowledge. Some treatments for infections consisted of ointments prepared from cats that had been roasted in hedgehog fat.Mortimer, (2009) p. 211 Among the plethora of diseases that caused childhood death were measles, influenza and smallpox.Pickett, p. 10 The Crusades and the Muslim conquests aided the spread of smallpox, which was the cause of frequent epidemics in Europe following its introduction to the continent between the fifth and seventh centuries.Clark, p. 21
Measles was endemic throughout the highly populated countries of Europe, North Africa and the Middle East.Gilchrist, p. 41 In England the disease, then called "mezils", was first described in the 13th century, and it was probably one of the 49 plagues that occurred between 526 and 1087. Rinderpest, which is caused by a virus closely related to measles virus, is a disease of cattle known since Roman times.Barrett, p. 15 The disease, which originated in Asia, was first brought to Europe by the invading Huns in 370. Later invasions of Mongols, led by Genghis Khan and his army, started pandemics in Europe in 1222, 1233 and 1238. The infection subsequently reached England following the importation of cattle from the continent.Barrett, p. 87 At the time rinderpest was a devastating disease with a mortality rate of 80–90%. The resulting loss of cattle caused famine.
Early to late modern period