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.

A. Supernatural origin of disease?

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

Disease is associated with bad air-”miasmas” with a sort of spiritual component

“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 cities

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!

Types of Germs and Their Diseases

• 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