Download 1 Disease and Death 2

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Disease and Death
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The Effect of Disease on Human History
† Epidemics
and plagues wiped out vast numbers of the population in a wide area.
† Persistent infection in certain regions have made human habitation impossible there.
† Overall endemic low-level diseases throughout human civilization have produced low
levels of health and shortened life expectancy.
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Often the result of inadequate diet.
Hunting and Gathering Groups
† Hunting
and gathering ranged over a wide range of food.
† Malnutrition was rare.
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Food consumption was as high if not higher than the earliest agricultural groups.
Deficiency diseases would have been rare.
Hunting and Gathering, 2
† Modern
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Hunting and Gathering, 3
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Death in childbirth and infant mortality would likely have been high.
Probably no worse than early agricultural societies or even early modern Europe.
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Life expectancy was short, though older people would not have been unknown.
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hunting and gathering groups suffer from intestinal parasites, such as worms.
These may have been common in prehistoric groups, especially in Africa.
The spread of civilization out of Africa into temperate climates would likely have reduced this
problem.
In France, ¼ of all children died before their 1st birthday.
Among the San of Africa, about 1 in 10 are over 60.
Early Agricultural Societies
† Agriculture
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exposed humans to a range of diseases not previously encountered.
Result was a major deterioration in health.
† Settled
societies meant that increasing numbers of people were living in close proximity
to each other.
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This increased exposure to infectious disease.
Relation of Animal and Human Diseases
† The
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domestication of animals exposed people to diseases which affected animals.
In many cases domestic animals shared the same living quarters.
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animal diseases adapted to human hosts and flourished unchanged.
altered their characteristics and became human diseases.
† Others
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Relation of Animal and Human Diseases, 2
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Many common human diseases are close relatives of animal diseases.
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Smallpox is similar to cowpox.
Measles is related to rinderpest and to canine distemper.
Tuberculosis and diphtheria originated in cattle.
Influenza is common to humans and hogs.
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The common cold came from the horse.
Leprosy came from water buffalo.
Humans now share 65 diseases with dogs, 50 with cattle, 46 with sheep and goats, and 42 with pigs.
The Problem of Greater Concentration of Population
A large number of people living in cities of several thousand or even villages of a few hundred posed a
major problem of waste disposal.
† Few early societies kept human excrement out of their drinking water.
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Infectious Diseases Require Crowding Together
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The steady rise in population and increasing density allowed new diseases to become established.
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Many infectious diseases (e.g., measles, mumps, and smallpox) require a minimum number of human hosts to
survive.
Measles will die out on islands with a population of less than ½ million.
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Most used one watercourse for both purposes.
The mixture of water and human waste was a perfect habitat for intestinal parasites such as worms.
Diseases such as cholera and dysentery were endemic.
The cities of Mesopotamia reached population levels this high.
Other cities were close enough to make contact between them frequent.
Irrigation
† Agriculture,
as opposed to gathering naturally growing wild crops, alters the environment
in was that encourage the spread of disease.
† Agriculture required artificial irrigation.
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The ditches that were dug held slow moving water that provided prime breeding grounds for
parasites.
Disease from Irrigation
Schistosomiasis, a blood fluke, causes extreme debilitation and listlessness.
† The blood fluke has an elaborate life cycle involving both humans and water snails at different stages.
† Irrigation ditches were ideal habitats for water snails. People working in the ditches were exposed to
infection from the fluke.
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Schistosomiasis
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The disease was widespread in early societies such as Mesopotamia and Egypt that depended on large-scale irrigation.
Over 100 million people suffer from schistosomiasis infection today, many of them in Africa.
Malaria
† Forest
clearance, by the swidden system of slash and burn, created pools of standing
stagnant water that were breeding grounds for mosquitoes.
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Mosquitoes carry malaria. When they bite humans, malaria spreads.
Malaria, 2
In West Africa, malaria had been unknown before agriculture became established. Now it is endemic.
In China the spread of settlement southwards from the Yellow River valley into the wet rice-growing
areas of the Yangtze exposed the population to malaria and schistosomiasis.
† In India the spread of agriculture from the Indus valley into the wetter and warmer Ganges valley
exposed settlers to a range of new diseases, especially malaria.
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Disease Pattern of Settled Societies
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Diseases flourished in towns and cities, because of lack of sanitation and crowding.
Until the 19th century in Europe and North America, cities required a constant influx of people to
sustain their numbers because of the high death rates.
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This is still the case in much of the rest of the world
At first new infections would cause many deaths because there was no acquired resistance in the
human population.
Over time a degree of immunity would develop.
Low-level Endemic Disease plus Periodic Epidemics
A continuous low level of disease was characteristic in ancient societies.
This was interrupted by virulent outbreaks killing large numbers in a short period.
† Most of the surviving records are not specific enough to identify the diseases. (They were all called
“plagues.”)
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Separate Developments in Widely Spread Societies
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The major areas of human population had little contact with each other in the early phase of civilization. I.e.,
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The Mediterranean
The Near East
India
China
The Americas
Oceania
Diseases established in one area were unknown in others. Where a disease was established, the population had
developed a level of immunity.
When contact was established between societies, diseases spread with lightning impact.
Example: Smallpox
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The Roman Empire suffered a great “plague” in 165 CE, with death tolls of around ¼ of the population.
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The disease was probably smallpox, which was new to the Mediterranean area.
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Tuberculosis can be identified as early as 3000 BCE.
Most of the major epidemics are more likely to have been more virulent forms of present day diseases such as
measles.
And suffered further outbreaks periodically over the next five centuries.
Spread from India
† China
had similar outbreaks in 161-162 and 310-312 CE, when death tolls reached 40%
in many places.
† Smallpox was known in India before this time and the population there had developed
some immunity to it.
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Leprosy
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It was likely carried to the Mediterranean and to China by traders who were themselves immune,
but who could transmit the disease.
A similar disease to spread from India in the 6th century was Leprosy.
It became one of the major diseases affecting the population of Europe.
Leprosy, 2
† In
the 13th century there were 19,000 lazarets (clinics) to accommodate and isolate
infected people.
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The disease died out in Europe after the 14th century. The population slowly built up immunity.
Death rates fell as the disease became endemic, but less virulent.
Bubonic Plague
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Another epidemic disease that first appeared in India was bubonic plague.
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Bubonic Plague
† It
broke out in the Mediterranean in 542, arriving by a ship from northeast India, spread
by fleas on black rats.
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The population was vulnerable and the death rate was high.
† The
disease arrived in China in 610, again by boat from India, and killed about ¼ of the
population.
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The return of the plague in the Middle Ages
† Better
links for human contact and a larger and more densely packed population made the
effect of the disease more catastrophic when it returned in the Middle Ages.
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The Mongol Empire
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The Mongol empire that came to dominate Asia in the Middle Ages stretched from European Russia
and the Near East to China.
The Spread of the Plague along Trade Routes
The Mongol Empire opened up trade across the steppes of Russia and the deserts of central Asia.
The burrowing rodents of the area, which were infected with bubonic plague and carried infected fleas,
spread into China.
† Plague broke out in China in 1331 and spread along the caravan routes to reach the Crimea in 1346,
and then to the Mediterranean.
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It was spread further by ships carrying black rats and infected fleas throughout Europe, where it was known as the
Black Death.
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The Black
Death
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The Black Death
The disease was characterized by buboes, which are swellings of the lymphatic glands, with secondary
swellings in other parts of the body.
† The progress of the disease:
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Extreme pain, followed by fever, vomiting, delirium, and death.
The swellings, the excrement, vomit, blood, everything in the infected person turned black before death.
The Black Death, 2
There were two forms:
† The bacterial form spread by fleabites and killed in three or four days.
† An even more virulent pneumonic form spread from person to person could kill in a few hours.
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The Black Death, 3
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The Dance of Death. A popular theme in European art and literature after the plague. This fresco from the 15th century shows the grim reaper
dancing in turn with all the members of the society, showing no favourites.
The Black Death, 4
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In total about 1/3 of the population of Europe died in the initial outbreak.
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Many tried to flee, thereby helping to spread the disease across the countryside.
After the first outbreak in 1346-1349 bubonic plague reappeared at intervals for centuries.
Between 1347 and 1536 there was a major outbreak somewhere in Europe on average every 11 years.
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In the period from 1536 to 1670 it averaged once in 15 years.
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The Black Death, 5
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In the 17th century, 2 million people died of plague in France.
The Great Plague in London in 1665 was brought from Amsterdam and spread across the city.
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Endemic Disease in the Americas
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It is likely that the urban areas in the Americas – the Aztec and Incan empires, for example – had
crowded and unsanitary conditions producing intestinal parasites and dysentery similar to the Old
World.
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About 6000 people a week were dying of the disease in London.
The plague began to die out in northwest Europe in the late 17th century, but remained endemic in
eastern Europe and the Near East.
It is certain that the major endemic diseases of Eurasia had not spread to the New World.
The lack of domesticated animals in the Americas meant that diseases did not spread from animals to humans there
as they did on other continents.
Arrival of the Europeans
The Spanish conquistadors brought with them a wide range of European diseases.
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Smallpox, 1518-1526 – many millions died.
Measles, 1530-1531
Typhus, 1546
Influenza, 1558-1559
Estimated casualties:
† In central Mexico, the centre of the Aztec empire, the population fell from 25 million before the conquest to 1 million in
1600.
† The effect was to completely destroy the flourishing Aztec society.
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Process Repeated
† Similar
collapses occurred throughout the Americas from Peru to Canada as European
diseases spread through the New World.
† The process was repeated in the next centuries by the arrival of slaves from Africa
bearing more diseases endemic to their society. Examples:
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Malaria, early 17th century,
Yellow fever, 1648.
And New Diseases for Europe
† Syphilis
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Syphilis
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Did it originate in the Americas?
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was a disease not known in Europe before the 1490s.
It was noted during the French army invasion of Italy in 1494.
It then reached India in 1498 with the sailors on Vasco da Gama’s voyage.
By 1505 it had reached China and Japan.
In the 15th century, people were convinced that syphilis originated in the Americas and was brought back by the
sailors from the first expeditions.
The first recorded appearance was in Barcelona in 1493, a year after Columbus’ first voyage to the Americas.
There is controversy over this. Another view is that it was a form of the disease yaws already endemic in Europe.
Other New Diseases
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Typhus – Brought to western Europe from Cyprus by Spanish soldiers in 1490.
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Transmitted by lice. This was first discovered in 1910. Delousing stations were set up during World War I.
Armies and navies were among the main mechanisms for the spread of new disease. They lived in primitive
conditions of overcrowding and poor sanitation, and traveled to and from new locations.
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Until the 20th century, armies nearly always lost more soldiers to disease than to battle.
Other New Diseases, 2
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Cholera – Transmitted through drinking water polluted with human wastes.
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Was endemic in Bengal and had spread to adjacent areas.
In 1817 British troops carried it from Calcutta to the north of India.
It spread to southeast Asia and then to East Africa in 1821.
In 1826, it infected the Russian army. By 1831 it reached the Baltic.
From there to western Europe, the United States and Mexico.
Caused panic in Europe where primitive water supply and sanitation systems allowed the disease to spread rapidly.
It was only countered through improvements in sanitation through the 19th century.
Winning the Battle Against Infection
† The
pattern that has existed throughout human history has been broken in the last 200
years in the industrialized nations.
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Life expectancy has increased dramatically.
Infant mortality has all but disappeared in the developed nations, except for those with inherited or
incurable diseases.
† Reason:
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The Decline in Infectious Diseases
† Factors
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these have all had a minor effect relative to the overwhelming importance of:
Better diet.
Improved environmental conditions.
Diet and Public Health
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Diet
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Public Health
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in the decline of infection:
Some diseases have evolved into less virulent forms.
Vaccines.
Antibiotics.
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Fewer are killed by infectious diseases.
In the 19th century, the quantity and quality of food available in the industrialized nations improved significantly.
Effective sewers and treated drinking water reduced water borne diseases such as cholera.
Better Housing, which reduced overcrowding, damp, and poor ventilation.
Prevention of food contamination: Pasteurization of milk, canning, and refrigeration.
The Battle Goes on in the Third World
The main causes of disease are still widespread in the Third World. The patterns of disease that affected
the entire world for thousands of years are still prevalent outside of the industrialized nations.
† Diet: Chronic malnutrition or starvation still common.
† Public Health: Sanitation conditions still poor in many parts of the world. Especially contaminated
water.
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Leads to widespread intestinal infections, especially in children.
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Water Related Diseases in the Third World
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Successes and Failures
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Immunization programs:
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Successful with smallpox.
Less successful with malaria.
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Plague
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Influenza
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Controlled, but not eliminated.
Virulent strains still appearing.
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Aids
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First recognized in 1980s. May have crossed from monkeys. No vaccine available.
Infection rates rising rapidly, especially in Africa.
Diseases of Affluence
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The decline in infectious has been paralleled by the rise of new diseases born of affluence.
Cancer
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Heart disease
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The 1918 outbreak swept the entire world, resulting in 15-20 million deaths. (Especially in Europe where people had been weakened by poor diet due to
World War I.)
European cancer rates are 10 times higher than those in West Africa.
Almost unknown 100 years ago except among the rich who had a diet high in fat and sugar.
Now kills 40% of men and 20% of women in industrialized countries.
Reasons for the rise of diseases of affluence
† May
be partly because people don’t die of infectious disease and live long enough to get
cancer or heart disease.
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We are healthy enough to fight off many infections and sanitation has removed many parasites that
plague poorer societies.
† But
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other reasons for cancer and heart disease suggest themselves…
Reasons for the rise of the diseases of affluence
Change of diet in the wealthy nations.
† Reduction in fibre intake.
† Rise in sugar consumption.
† Higher levels of fat in the diet.
† Higher proportion of processed foods.
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Reasons for the rise of the diseases of affluence, 2
Intentional and non-intentional intake of hazardous chemicals.
† Tobacco use.
† Toxic chemicals in the atmosphere, in water, and soil.
† Pesticides and herbicides.
† Food additives.
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