‘There has been a disease crisis whenever people have made radical changes in their lifestyle and environment.’ Discuss.

            New diseases have been continually evolving and have had considerable impact on the way society has developed, its religions and its prejudices. Each change in habitat has led to the end of some diseases and the start of some new ones. William H. McNeil was the first Historian to see disease as a key factor in our History. He cited examples such as the epidemics which led to the fall of the Roman Empire and the colonisation of the new world. Something unusual must happen to start epidemics and throughout history the radical changes in lifestyle and environment have often led to disease crises. An epidemic usually strikes very quickly, with isolated communities such as islands especially vulnerable to them. Soon after the outbreak of an epidemic most of the population is either dead or immune. The microbes having run out of susceptible hosts, die off. Only years later can the germ successfully attack again, depending on an accident of reintroduction.

            The first great change in lifestyle and environment was when the early hominids left tropical rain forests for the savannah. They were part of a relatively balanced eco-system but with the change in habitat they encountered new viruses, such as sleeping sickness, from the animals they now hunted.

            People then spread from Africa to the rest of the world. Moving from tropical to temperate climate, necessitated the invention of clothes which created a home for lice, which spread disease. Humans escaped the parasites of the tropics like worms, parasites and now had fewer animals and plants in the temperate climate. Karlen saw the change leading to man coming into contact with new diseases such as trichinosis. At this stage the numbers living together were too small for ‘crowd’ diseases to take over.

            The adoption of agriculture was the next radical change in lifestyle and environment. People ‘settled down’, living in much larger groups with population densities between ten and a hundred times greater than before. They also began to integrate with other communities. This has been described as the biggest change in lifestyle and environment that humans have experienced.  It led to a disease crisis in which  people fell to scores of diseases they had never known. The diseases could be transmitted in new ways. Farmers now lived amongst their own and their animals sewage which spread disease. Disease spread through drinking water. Using irrigation and animal excrement on crops also lead to the spread of disease. Scavenging birds and rodents that carried diseases were attracted by stored food. Many of the new diseases came from domesticated animals. The diseases that they carried transmitted themselves in different ways. They could catch disease straight from animals or from pathogens, organisms that causes disease which were transmitted to humans after we had disturbed animal lifestyles. There were also diseases which had jumped from animals and became completely new diseases. These included measles which came from cattle and influenza from pigs and ducks. At this time each geographical region had it own diseases, ‘disease pools’ which existed in relative isolation from each other.

            The next great lifestyle and environmental change saw the confluence of the civilised disease pools of Eurasia. It lasted from 1400BC-1200AD. The Mediterranean, which was one of the last areas to be colonised is an example of the confluence. Diseases present there included mumps, diphtheria and influenza. Plague, measles and smallpox were not present in the Mediterranean, while at the same time smallpox was permanently established or endemic in India. It had a short incubation period and at first could not reach the Mediterranean because it would have died out on the way across. However, if diseases managed to move from one civilisation to another they would have a devastating effect. The diseases usually arrived by sea and it was therefore trade which lead to the spread of disease.

            The Plague of Antoninus was the first time a new plague from Asia arrived in Europe. Roman troops were in Syria to crush a revolt in 164AD. When they returned home two years later they carried the infection with them. It spread to every corner of the empire and lasted for 14 years. It killed 6 million people, including about a third of Italy’s population. .

            By 1300 many diseases were gradually becoming endemic in Europe. However,  the Black Death was seen as ‘Europe’s greatest environmental crisis’. It was an epidemic of bubonic plague between 1346 and 1351, which returned in 1361 and again in 1369. 20 million died in Europe alone. It killed a third of the population and significantly more in some places. The areas which suffered the most included ports, larger towns and the densely populated countryside. There is considerable debate over the origins of the plague but the spread of the black rat, which lived near human dwellings was undoubtedly a factor. Many historians think the plague was caused by  a micro-organism occurring among rodents. It was transmitted by blood sucking fleas, normally rat fleas. The bacilli are able to survive for long periods among rodent communities, without being a hazard to humans. But periodically, they spread from rats to other, less tolerant rodents. As the rodent hosts die the fleas turn from rats to people. Therefore it is a disease dependant upon combination of bacilli, rats, fleas and humans, aided by the correct climatic conditions.

            Some historians think that before the plague struck Europe was ‘ripe for a disease crisis because of population rises. By 1300 Europe was already a ‘full world’. New land being brought under plough was of progressively poorer quality. Climate changes were also significant. Colder, wetter conditions led to poorer harvests which meant people were worse equipped to resist the plague. The crowded and insanitary urban conditions, like open sewers, enabled disease to spread rapidly and occur frequently. The Black Death resulted from these radical changes.

            Prior to the arrival of the Europeans the New World was stable but it proved disastrous for them when they met the Old World. The European invasion of the New World was certainly a radical change in both lifestyle and environment. The consequences have been described as a ‘holocaust’ with no human author. The Amerindian population in 1492 has been estimated at between 75 and 100 million, although this remains a subject of great controversy. It had fallen to 250,000 by 1750 - mainly due to epidemic disease. A similarly dramatic fall was experienced in Central Mexico where the population plummeted from 25 million in 1492 to 1 million in 1568. While disease was not the sole factor, it was indisputably the most prominent factor. The Amerindians had not learnt to live with the diseases from dogs, pigs and cattle so they had no immunity. They experienced the epidemics as ‘virgin soil’. It was as though they were in the middle ages as their diseases had had little time to develop compared to the Europeans. They did not trade between themselves and had no domesticated animals. So when the European ‘crowd’ diseases hit they were devastated. Small or isolated populations like the Americas can’t ‘hit-back’ with their own diseases. Smallpox which was endemic in Europe was the major killer. It had a 40% mortality rate in those experiencing it for first time. It spread through human breath which made it extremely contagious. In later years other old world diseases followed including mumps, typhus, typhoid, scarlet fever, yellow fever and influenza.

            However, there were many other factors coupled with the diseases which caused the devastation. The epidemiological onslaught psychologically overwhelmed the Amerindians.  Many natives saw the diseases as divine retribution. Because the religious and political systems of the tribes were inextricably linked this caused political collapse and natives fled from their societies. The ‘doom-ridden’ people had lost the will to live. They also lacked adequate nursing to cope with the disease and their main method of curing people by making them ‘sweat it out’ proved useless against small-pox. It has been put forward that it was primarily Spanish military superiority that caused the decimation of the population. The Spanish had horses, armour, metal, guns and hunting dogs. Their technology was vastly superior to that of the Incas who had not even invented the wheel. They treated the natives terribly, making them work in deadly mines, although this was not the major factor. They also had more advanced communications, for example writing. However, McNeil says: ‘It was clear that if smallpox had not come when it did, the Spanish victory could not have been achieved in Mexico’. Disease also had a huge effect in Peru where the reigning Inca, his son and heir died, leaving no clear successor. Another example that disease was the major factor in the Amerindians demise was that the Aztecs did indeed defeat the Spanish. However, on the very evening that the Aztecs drove the conquistadors out of Mexico City, a smallpox epidemic broke out. The New world disease crisis demonstrates the important role disease has played in world history.

            The Industrial Revolution saw great changes, creating huge cities with overcrowding and poor sanitary conditions. Cholera killed thousand of people in cities like London which had sewage on the streets and giant cess pits. At this time few people associated cholera with urban squalor.

            The greatest pandemic in history was the 1918 influenza epidemic. It affected Asia, Europe and North America, killing 40 million people. It was able to spread in Europe partially because of the poor sanitary conditions in cities like London. The fact that many more died than in the Great War showed the power of disease. 

            Today, we are experiencing new diseases which are a result of the dramatic changes in lifestyle this century. Developments such as inter-continental travel, hugely populated cities and globalisation have lead to the spreading of many new diseases, including Ebola Fever, 1976 and Toxic Shock Syndrome, 1980. The destruction of the environment such the tropical rainforest is also significant because it unleashes diseases which were previously no threat. New social behaviour such as an increase in promiscuity has led to new diseases such as AIDS which was discovered in 1980. There are also disease caused by modern farming methods such as B.S.E because people want a larger amount of food but are not prpared to pay extra for quality. Pollution in cities has led to an increase in diseases like asthma.