Download Set 1 Ideas about diseases

Emerging Diseases
Lecture 1:
Historical Ideas About Infectious
Diseases
1.1 Overview
1.2 Historical Ideas About Infectious Disease
A. Supernatural
B. Humoral
C. Miasma
D. Germs
1.1 Overview: Types of Diseases
There are many types
• 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
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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.
A. Supernatural
origin
of disease-an early
idea
Not a useful idea
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
Hippocrates
Humoral Hypothesis
Humor = body fluid
Mood, personality are
determined by your own
individual mix of humors
Disruption leads to illness
Restoring the balance of Humors
Many things might force the humors out of balanceThe important thing was to restore balance
“bleeding” or “bloodletting” was a key treatment
Used 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-so physicians
actually had a chance to cure disease
• He was 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
• His ideas persisted for over 2000 years in Western
society
C. Miasma
Humorism 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 only 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 seemed to fit the facts
Miasma idea about
infectious disease
Disease is associated with bad air”miasmas” with a sort of spiritual or
ghostly component-not a physical thing
“Miasmas” resulted from the chemical
breakdown of living material
19th Century cities were a
good place
for this
Sanitarians were
determined to clean
up the filthy cities
Sanitarian movement of the 19th
Century
• 19th Century cities had many diseases of filth
• Sanitarians operated under the idea that
cleanup would reduce miasmas and therefore
disease
• But even if that didn’t work everyone was
better off if the cities were cleaner
• They convinced city governments to act
• Built privies and sewers, paved streets and
tried to keep them clean
Sanitarian ideas were fuzzy
They thought disease resulted spontaneously from
garbage, filth and dirt
Thought chemical interactions produced miasmas and no
host was necessary for miasmas to proliferate
But they thought cleaning up was generally a good idea
And some key medical people of the mid-1800s agreed
Cleaning up the garbage,
sewage and dirt did make a
difference! Sanitarians helped
to improve public health!
Their ideas were wrong but
their actions were helpful.
D. Germ Theory of Disease
Many other 19th Century medical professionals
suspected that something more defined than a
miasma was responsible for some diseases
• The “contagionists” felt that physical things caused
disease-not mysterious vapors
• Actually an old idea (smallpox germ warfare used
against Native Americans)
• 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 always come from pre-existing microbesnot miasmas
Specific microbes are always associated with
specific diseases
Robert Koch
Anthrax
Koch showed that germs caused diseases
Koch’s Postulates-rules for demonstrating
causation
Endospores of anthrax
are very stableA bioterror weapon used
against the US in 2001
In 1854 Dr. John Snow halted a
deadly cholera outbreak in
London by preventing contact
with contaminated water –
showed something physical
must be involved
Semmelweis-”The Savior of Mothers”
• Puerperal fever or childbed fever
• Semmelweis notices higher incidence
when doctors deliver-not midwives
• Suspects dirty hands or instruments
• Cleaning instruments, hands and
clothing reduced post partum
infections
Lister-Antiseptic Surgery
• Used strong chemicals to kill germs
• “Carbolic acid” = phenol = paint stripper
• “Antiseptics” = chemicals that kill germs on
surfaces
• Achieved a significant reduction in
post-surgical complications and infections
Through the work of Pasteur, Koch, Snow,
Semmelweis, Lister and many others The
Germ Theory of Disease
Became accepted by scientific 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 Disease
so successful and still so widely
accepted?
Because it is based on a lot of evidence
and………
IT WORKS!
If it didn’t work we would have to come up with a new theory.
Types of Germs and Their Diseases
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Parasites-tapeworms, amoebas, protozoa
Fungi- athlete’s foot, yeast infections
Bacteria-anthrax, syphilis, Staph infections
Viruses- AIDS, cervical cancer (HPV), influenza
Sub-viral- Mad Cow, Hepatitis D
These are just some examples of five important
types of germs