Immune System Summary
 There are three lines of defense a
pathogen must defeat in order to
create a problem/illness/disease
in our bodies.
1) Skin and Mucous Membranes
2) Non-specific Immune
Responses (Macrophages,
Neutrophils, fever,
inflammation)
3) Specific Immune Responses (B
cells, T Cells, Antibodies)
Immune System Summary
 To get by the first line of defense,
skin and mucous membranes,
the pathogen must either find a
break in the skin (i.e. cut) or use
a pre-existing entryway.
 Most common entry points after
a cut or scrape are through the
respiratory system (nose and
mouth), through the gastrointestinal lining (we eat it) and
lastly through the genitourinary
tracts.
Immune System Summary
 To beat the other lines of
defense, the pathogen uses
biochemical trickery.
 It either blocks the immune
cells from recognizing it as
foreign or it terminates them.
Pathogens want inside us
 All human pathogens
want to get inside our
body in order to
multiply.
 The human body’s core
temperature is in the
optimal range for the
reproduction of most
pathogens.
Transmission Definitions
 Transmission can be generally classified as:
 Airborne: pathogens that are in the air that are breathed
in.
 Waterborne: pathogens that are in water supplies that are
drank in.
 Foodborne: pathogens that are in food that is eaten.
 The following are ways that pathogens can enter the body
and may or may not fall under the above three general
categories.
#1) Insect-Borne Vectors
 Insects form a large
portion of pathogen
vectors because many of
them are hematophagic,
meaning they feed on
blood at some point in
their lifecycle.
 Mosquitoes, ticks, lice,
fleas and some flies are
examples of insect vectors.
 Other animals can be
vectors as well, but not as
common as insects (i.e.
rats, mice, cows, deer…).
#1) Insect-Borne Vectors
 The pathogen is picked up by the vector insect at some
other point and transferred to the human host in
many ways, each circumvents the first line of defense,
the skin.
#1) Insect-Borne Vectors
 Some insect vectors pierce the skin with a specialized
mouthpart (i.e. mosquito).
 Others simply bite the skin and create a pool of blood
(i.e. black fly)
 The triatomine bugs, responsible for passing on the
protist which causes Chagas’ disease, defecates the
pathogen out while it feeds and the host rubs it into
the wound in response to the bite!
 All these methods pass the pathogen right into the
bloodstream where it can do the most damage.
#2) Droplet Contact
 Many pathogens require
the air to provide a
pathway to infect other
hosts.
 The pathogen particles
travel from one host to
another through the air
in a cough or a sneeze.
 The pathogens get in the
body through the
respiratory tract.
#3) Direct Contact
 Pretty straightforward…
 An infected person with
outward signs of
infection makes physical
contact with an
unaffected individual
and passes on the
pathogen.
 In many cases the
contact is sexual.
#4) Indirect Contact
 An infected individual
touches a surface and leaves
the pathogen on that surface.
 An unaffected individual
touches the same surface
later on and picks up the
pathogen.
 Pathogen only gets in if that
body part contacting the
contaminated surface is then
placed around an entry into
the body (i.e. hand in
mouth).
 Some, like ringworm, don’t
need entry.
#5) Fecal-Oral
 An affected person does
not wash their hands after
going to the bathroom and
transfers a pathogen to a
food source that is then
eaten.
 Can also happen if raw
sewage mixes with
drinking water.
 Most foodborne pathogens
are through this method of
transmission.
#6) Vertical Transmission
 This is when an affected
mother passes the
pathogen on to her
developing fetus through
her bloodstream.
 Usually sexually
transmitted diseases
(STDs) like HIV,
Hepatitis B, Syphilis,
etc…
#7) Airborne (aerosol)
Transmission
 Not a natural way for a pathogen to be released.
 This is where a pathogen is released in tiny droplets of
water that hang in the air for long periods of time.
 Considered bioterrorism.
 The USA has “BioWatch” to analyze air samples and ensure
terrorists have not released pathogens into the air over a
major city center.
Homework
1) What the three lines of defense a pathogen must
break through in order to cause illness in a human.
2) Indicate 5 places on the human body that a pathogen
may try to enter.
3) For each type of transmission, indicate two
pathogens (as specific as possible) that follow that
method of infection.
4) Other than vertical transmission, indicate one way
you could protect yourself against each type of
transmission.