A Green History of the World Part 8




VINTAGE BOOKS              2007



Chapter 10: Disease and Death

The way in which humans have lived and the environments they have created have had a profound effect on their health, life expectancy and the causes from which they have died. It is yet another example of the influence of the environment on human history. Disease have made their impact on human history in three main ways. First, there have been the highly lethal outbreaks of disease such as the ‘Black Death’, which killed almost a third of the population of Europe during its first outbreak in the mid-fourteenth century. Second, there have been the persistent, endemic diseases such as trypanosomiasis (sleeping sickness), malaria and schistosomiasis, that have either ruled out areas for settlement or produced long-term debilitation. Third, the inadequate diet on which much of the world’s population has had to survive has resulted in deficiency diseases and general poor health, making people more vulnerable to other diseases.

The pattern of disease and death has been affected by four major developments in human history. First, the creation of farming communities opened humans to a whole range of diseases that originated with animals. In addition, permanent settlements made it difficult to provide clean drinking water and a number of diseases became endemic. Second, the development of cites brought humans together in numbers sufficient to allow the major epidemic diseases to develop and eventually spread. Third, the gradual drawing together of human communities around the globe, first within Eurasia and then when Europeans reached the Americas and Oceania spread new diseases to peoples who had not natural resistance. Finally, in the industrialized world in the late 19th century improvements in public health significantly altered the impact of diseases long before effective medical treatment became available in the 20th century. Medical treatment had a significant but limited impact and, by the late 20th century, it faced a new threat from the changing pattern of disease.

The diseases of agriculture

  • There is little doubt that the adoption of farming and the subsequent rise of settled societies led to a significant reduction in human health in a number of ways.
  • The domestication of animals for the first time brought humans and various animals into close contact – animals often lived alongside humans inside the primitive houses. Many disease that were endemic to particular animal species were able to adapt, mutate and jump to humans.

The result is that after living for almost 10,000 years in close proximity with animals, humans now share 65 diseases with dogs, fifty with cattle, 46 with sheep and goats, 42 with pigs, 35 with horses and 26 with poultry. Although many of these diseases took time to develop because of low population densities, they were to have a huge impact on human history.

  • The first impact of disease in early settled societies would have been caused by poor or non-existent sanitation.
  • Second, the development of irrigation in the first farming communities led to the spread of schistosomiasis, a fluke that causes extreme debilitation and listlessness.
  • Third, the adoption of agriculture would have produced a number of deficiency diseases through the much reduced variety of food available. Storage for long periods reduces the level of a number of key vitamins and nutrients.
  • The first deficiency disease to emerge was anaemia caused by iron deficiency. It was the result of cereals making up too high a percentage of the diet and inhibiting iron absorption.
  • In the Americas the disease emerged as soon as maize formed a large part of the diet.
  • In China beriberi caused by thiamine deficiency and leading to nerve problems and a swelling of the face and limbs was common by 2000 BCE. It was caused by a diet too high in rice (usually over 80%) when too much of the outer husk of the rice was removed.
  • Scurvy, caused by a lack of vitamin C, was endemic across the world wherever there was a lack of fresh fruit and vegetables in the diet. It can first be identified in Egypt about 1500 BCE.
  • The disease was particularly prevalent on European ships making long sea voyages after 1600 and it probably killed about 1 million sailors in the next 200 years.
  • Perhaps the strangest of food diseases was ergotism which was common in Europe from around 600 CE until about 150 years ago. It was caused by the ergot fungus on grains, especially rye, and developed because of damp conditions especially during planting and later in storage.

Overall the health and life expectancy of these agricultural societies was very poor. In the Levant in the early Islamic period (around 700 CE) the average age of death was the same as it had been in the earliest farming villages about 9000 BCE. In Scandinavia around 1200 CE the average lifespan was about 18 years and half of all individuals died as children. A detailed study of over a hundred cemeteries north of the Alps dating between 1000 and 1200 CE shows that, apart from the very high infant mortality rate, a third of males and a quarter of females died between 14 and 20 (mainly from malaria, smallpox, dysentery and tuberculosis). Overall less than a quarter of the population survived until they were over 40. The result was that these societies had a very different population structure from modern societies. Only about 5% of the population were aged over 65 and children, not the old, were the main class of dependents.

The ‘Great Plagues’ and their spread

After the emergence of settled societies it was the development of the first cities with their large and concentrated populations that began to expose humans on a major scale to the diseases that had originated with animals. Infectious diseases such as smallpox and measles that do not depend on transmission through water or another host species require a minimum number of human hosts in order to survive.

  • If the population is less than about 250,000 measles will die out. There would have been no more than short-lived, local outbreaks of these infectious diseases until relatively large cities began to develop.
  • The impact of these diseases was affected by another key element in the history of disease – the growth of trade and travel enabling diseases to spread relatively quickly from one area to another.
  • In 1950 there were still 50 million cases of smallpox every year and over the course of the 20th century about 300 million people died from the disease.

The third of the ‘Great Plagues’ of human history was bubonic plague. The disease is caused by a bacterium that usually infects rodents (particularly rats) and their fleas. Humans can be infected by flea bites and this usually happens after a major outbreak of the disease among rats, causing a high death toll which forces the fleas to shift to feeding on human blood. Humans have little resistance to the bacterium and cells in the area of the bite die quickly, creating a blackening pustule and blister. The disease spreads through the lymphatic system, causing swelling of the nearest lymph node (usually the groin or the armpit), which swells to the size of an orange about 4 to 6 days after the original bite. Within 10 days of the bite about 60% of those infected die. Some develop a secondary lung infection and produce an airborne form of the disease which is almost always fatal.

  • The plague arrived in China in 610 (on a boat from India) through the port of Canton where it killed about a quarter of the population. There were more outbreaks of the disease in Europe until the 770s but then, for reasons which are unclear, it seems to have died out for almost 600 years.
  • Much more is known about the next and most serious outbreak of plague commonly known as “The Black Death’. Its spread demonstrates how trade and travel is central to the spread of diseases.
  • It began in central Asia in 1331 and reached France and England in 1347 and Moscow in 1350.
  • Everywhere the disease struck, death rates rose rapidly, especially once the pneumonic form took hold.
  • The impact of the plague in Europe, Egypt and the Levant was terrible and far worse than in China.
  • In Europe and other areas around the Mediterranean about a third of the population died, in many cities it was higher and only a few remote areas escaped altogether.
  • It produced human suffering and social dislocation on a huge scale as families were destroyed, communities collapsed and villages were abandoned.
  • The plague regularly returned to Europe for the next 350 years. During the 17th century about 2 million people in France died of the plague, including 750,000 in a single outbreak in 1628-32.
  • The last outbreak of the disease in England was the Great Plague of London in 1665.

The modern outbreak of the plague began in Yunnan in the mid-nineteenth century during the disruption caused by a series of major civil wars in China. It reached Hong Kong and Canton in 1894 and spread to Bombay (and the rest of India) two years later. In 1900 it reached Sydney and San Francisco. The result was that, for the first time, the plague bacillus spread to the rodents of Australia, the Americas and southern Africa, where it is now endemic. Europe is now the only area of the world which has no naturally occurring plague in rodents. (In the Americas 34 species of burrowing rodents and 35 species of fleas now carry the disease). There is no effective vaccine but modern medical treatment can reduce the death toll among those infected. The main area where it affects humans is now Africa, which has all but 1% of the world’s cases – there were 2118 known cases in 2003 and 182 deaths. Bubonic plague is only kept as a minor disease through public health controls – if these ever broke down it could return with devastating effect.

Other Eurasian diseases

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