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Emerging Diseases Lecture 1:
Historical Ideas About Infectious Diseases
1.1 Overview1.2 Historical Ideas About Infectious Disease
A. SupernaturalB. HumoralC. MiasmaD. Germs
1.1 Overview: Types of Diseases
• Nutritional or dietary diseases-scurvy, or vitamin C deficiency
• Genetic diseases-hemophilia • Behavioral diseases-addictions such as alcoholism• Mental illnesses-bipolar disorder• Infectious diseases-you can catch them from
someone or something-BIOL 119 Emerging Diseases is about this type of disease only!!
1.2: Some Historical Ideas About the Causes of Infectious Disease
• Supernatural – the anger of the gods• Humoral – balance of body fluids • Miasma - bad air• Germs – microscopic particles called germs
because they can “germinate” like a plant seed
These four have been historically important.
B. Humoral
• Greek physician Hippocrates formulated “humoral” medicine or “humorism”
• Body fluids were known as “humors”• When humors got out of balance-disease
followed• The four humors were yellow bile, black bile,
phlegm and blood• They were connected to “elements” earth, air,
fire, water
Humoral Hypothesis
Humor = body fluid
Mood, personality are determined by your own individual mix of humors
Disruption leads to illness
Hippocrates
Restoring the balance of HumorsMany things might force the humors out of balance-The important thing was to restore balance
“bleeding” or “bloodletting” was a key treatmentUsed up until about 1900 for almost any ailment including hemorrhage
There were other treatments to adjust other humors
Hippocrates is honored as the founder of the western medical profession
• He lived and practiced around 400 BCE• Main contribution was the idea that disease
had natural causes-not supernatural• The first major figure to draw a distinction
between medicine and religion• Hippocratic medicine is very different from
modern medicine but this was a huge step forward
C. MiasmaHumorism did not explain everything
well• For example-it was easy to see that certain diseases were
more prevalent in areas with bad sanitation and this was hard to explain based on the balance of humors
• It was proposed that rotting sewage and other materials gave off a polluted vapor or mist that caused various diseases when inhaled
• The mist was called a “miasma”• “Bad air”, “Night air”, “nebula”, “malaria” or “Cold air” were
other names for this horrible agent• “Miasma” explanation for disease
“Miasmas” resulted from the chemical breakdown of living material
19th Century cities were a good place for this
Sanitarian ideas were fuzzyThey thought disease resulted spontaneously from garbage, filth and dirtThought chemical interactions produced miasmas and no
host was necessary for miasmas to proliferateThey thought cleaning up was generally a good ideaSome medical people of the mid-1800s agreed
Cleaning up garbage, sewage and dirt made a difference!
D. Germ Theory of DiseaseMany medical professionals suspected that something less nebulous than a
miasma was responsible• The “contagionists” felt that physical things caused
disease-not mysterious vapors• But this explanation ran into trouble because no one
could see or demonstrate the existence of these physical things
• Improvements in microscopes and in science methodology changed all that in the second half of the 19th Century
Louis Pasteur
Showed that microorganisms always occur in infectious disease or in spoilage
And that they come from pre-existing microbesSpecific microbes are always associated with
specific diseases
Robert KochAnthrax
Koch showed that germs caused diseases
Koch’s Postulates-rules for demonstratingcausation
Endospores very stable
In 1854 Dr. John Snow halted a deadly cholera outbreak in London by preventing contact with contaminated water
Semmelweis-”The Savior of Mothers”
• Puerperal fever or childbed fever
• Semmelweis notices higher incidence when doctors deliver
• Dirty hands or instruments
Lister-Antiseptic Surgery• Used strong chemicals to kill germs• “Carbolic acid” = phenol = paint stripper• Antiseptics• Significant reduction in
post-surgical complications
Through the work of Pasteur, Koch, Semmelweis, Lister and many others The
Germ Theory of Disease Became accepted by scienctific and medical community around 1900.
The Germ Theory of Disease is the accepted theory today.
Infectious diseases are caused by germs!
Why is the Germ Theory of Diseaseso successful and so widely accepted?
Because it is based on a lot of evidence and………
IT WORKS!