HLTB21H3 Lecture Notes - Lecture 3: Social Inequality, Smallpox, Typhoid Fever
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HLTB21- September 19, 2013- Lecture 3
Infectious Disease and Human History
• Disease-causing pathogens have co-evolved with us
• With Homo sapiens’ expansion ~ 120,000 years ago: human- microorganism
contacts limited to infectious agents whose life cycles could accommodate
frequent residential shifts of migratory human gatherers and hunters
• Infectious diseases likely limited by small group size of early humans and their
relative genetic and behavioural homogeneity
> very densely unpopulated
• Spread of infectious disease restricted by transitory lifestyles and broad
geographical ranges of such groups
• With migration & population expansion: contact with disease
• Most dramatic shift in human-microorganism interactions occurred within past
10-15,000 years, due to agriculture and sedentism (non-migratory
lifestyle).....then urbanization and industrialization
Micro pathogens and worms are very effective pathogens that can wipe out a
population
The “Paleolithic Baseline”
Two classes of pathogens afflicted Paleolithic hunter-gatherers:
• Heirloom species: affected our anthropoid and hominine ancestors (prior to 6
million years ago) and continued to parasitize them as they evolved into
hominids; head and body lice, pinworms, internal protozoa, bacteria such as
Salmonella typhi and staphylococci, and possibly yaws
• Souvenir species: those that are “picked up” along the way (of daily activities); are
usually zoonotic pathogens whose primary hosts are non-human animals,
infecting humans only incidentally; zoonoses are passed on via insect and
animal bites, by preparing and consuming contaminated flesh, and via
contact with urine and feces of infected animals
Epidemiological Transition
• With expanding historical populations, mortality declined and structure of
causes of death shifted from predominantly infectious diseases to mostly
chronic degenerative diseases... (due to faster decline of infectious diseases
due to technological and behavioural changes)
Expanding, Stable and Declining populations
Population increased post-agriculture
Today we’re in a declining phase (in most Western nations)- more of us
dying than being born
Stable phase: adoption of birth control, which led families to decrease in size;
post WW2 when they’re not dying because of infectious disease but rather
with chronic diseases
- Clearly associated with changes in population
> Resulted in also good things, such as life span has increased as families have
decreased, medical technologies have become advanced
Preindustrial: 19th century Europe, LE increased to 40
Developing countries: 6- years LE
Life span reflects infectious disease spread
Measels: crowd disease-> larger populations living together in one place
Epidemiological Transition
• The Age of Pestilence and Famines
• The First Epidemiological Transition
• Agriculture and ↑ population ...
• Increase in infectious disease mortality
• Our ability to control animals; make them live in our community so we can
slaughter them
Agriculture and ...
• Food composition and nutritional quality
• Food processing technology and mastication
• Population growth
• Population distribution and health
• Work load and activity patterns
• You’re no longer isolated from people ; living closer with them
• After we became farmers, we worked harder than hunter-gatherers
The First Epidemiological Transition
Agriculture and ↑ population results in:
1. Occupational stratification : creation of different jobs; egalitarian society
(everyone’s responsible for their little parts that’s accepted by the
community) -> differentiation of social equality . Hunter gatherers
considered egalitarian, but farmers were more stratified (different levels,
usually social status and economic status, political power, etc)
2. Sedentism (being stationary; people living closely together and staying in one
place) & altered land use patterns (to farm tracts of lands)
3. Contamination of water sources : more people living together so more
infections
4. Within-group exposure to pathogenic microorganisms
5. Increase between- and within-group heterogeneity in susceptibility or
resistance to infectious agents
6. Increased group interactions (more frequently, longer pds)
7. Encroachment of human habitation (and agricultural fields) to wilderness
perimeters, thus increasing contact with vectors of zoonotic viruses and
bacteria (i.e., from domesticated animals) ; especially those living close to us
(for ex. sometimes people keep animals in their sheds)
Cultural evolution but also brought along great consequences
6 millions years, the majority were hunter gatherers, only in the 10,000 years
people have been farmers and not roaming around like hunter-gatherers
They could control how much food surplus they had
Hunter gatherers live in small band, spread out in the landscape and
essentially follow the food (animals) in order to hunt them, so you’re very
mobile, which has an effect in community size very small bands (i.e. 50)
Manipulating water sources, controlling water (irrigation, canals, etc.)
Dental Health
We lose teeth with cavity; we can also die from cavities because it destroys bone
• Caries
• Abscess
• Calculus deposits: build up of food that’s calcified on our teeth
• Tooth loss
• Tooth wear
Malnutrition
Protein malnutrition (and caloric) -> Meat becomes a status food -> consequences
for poor nutrition
• Mild-to-moderate micronutrient malnutrition
• Deficiencies in Vitamins A, B, C, D,
• Iodine
• Iron
• Ca
• Zn
• Anemia: deficiency in iron (today, cereals and breads have iron)