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Disease
EQ: How are diseases
transmitted?
Definition of a Disease
• The growth of a pathogen that begins
injuring cells and tissues
• Spread from contact with an infected
person or surface
Germ Theory
• Old school – disease was caused by an evil
spirit or by doing evil deeds
• Early Work – Pasteur and Koch showed disease
was actually caused by microorganisms
• Koch’s Postulates
– The microorganism is always found in the ill person
– The microorganism can be isolated from the ill person
and grown in a growth medium outside the body
– When the microorganism is then injected into a
healthy person that person gets sick with the illness
– The microorganism can be isolated from the newly
sick person
Agents of Disease
• Viruses
– Non-cellular particles that use the cell’s mechanisms to
reproduce more viruses and then ruptures the cell to
escape
– Examples: chicken pox, the common cold
• Bacteria
– Infect tissue directly growing in infected cells killing them
– Produce toxins
– Examples: lime disease, TB, flesh eating bacteria
• Fungi
– Rapid growth in skin tissues causing irritation and
infections
– Examples: ringworm, athletes foot
• Protozoans
– Small microorganisms
– Live in body and irritate body systems
– Examples: malaria, Montezuma's revenge
Non-Specific Defenses
First Line of Defense
• Not specific to any one pathogen
• Primary source of preventing disease from
infecting the body
Skin
– Acts as a barrier to
prevent bacteria and
viruses from entering
the body
– Very few pathogens
can enter through the
skin
– Very effective if
unbroken
• Bacteria and viruses
will enter through the
orifices like the nose,
mouth, and eyes
Mucus / Cilia
– All natural orifices are protected from disease
entering the body by tiny hairs and snot like
material
– Mucus is the silvery excretion that traps
particles
– Cilia are hairs that filter out disease particles
– Many of the secretions contain lysozyme
which is an enzyme that breaks down the
walls of bacteria
Phagocytes
• White blood cells that target and engulf the
invading disease particles
• Not specific to any particular pathogen
• Produced in the lymph nodes of the body
– this is why your lymph nodes swell when you
are sick
• Creates swelling at the site of a wound
• This is the pus when you pop a pimple
Fever
• A rise in the bodies temperature
– Stimulates the white blood cells
– Can kill some pathogens as they are taken
out of their ideal temperature range
– Should not always be treated with a drug
• As long as it is low grade it is doing more good for
your body than harm
• Only becomes harmful when it goes above 102
Interferon
• An enzyme produced by a virus infected
cell that helps block viral reproduction
• Slows down the infection so that specific
defenses can begin to work