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Infectious Disease
 Pathogen: Organism that causes
 Infectious disease: is a disease
that can pass from one organism
to another.
Four Kinds of
 1. Bacteria: are
MRSA Infection ~ Methicillin Resistant
Staphylococcus Aurous
Kinds of Pathogens continued
2. Viruses: reproduce
inside living cells
3. Fungi: Athlete’s foot
4. Protists: Malaria (1-3
Million Die/Year)
African Sleeping Sickness and
Athletes Foot caused by a
Each Pathogen is Unique!
 Every species of
pathogen has its own
unique antigen (large
protein that provokes
an immune response).
 For example, every
single virus that causes
influenza A, has a
antigen that is the
How Diseases are Spread
 Person to person transfer
 Contaminated Objects.
 Animal Bites.
The Three Lines of Defense
Against Pathogens!
 Immunity: is the body’s ability
to destroy pathogens before
they can cause disease.
 There are two types of
immunity: Active and Passive
Active Immunity
 Occurs when a person’s own
immune system produces
antibodies in response to the
presence of a pathogen.
 Example: Flu Vaccination
(Substance is called a vaccine)
 A vaccine is a dead or weak
pathogen that stimulates an
immune response.
 Active Immunity usually lasts
for many years, and sometimes
it lasts for life.
Passive Immunity
 Passive immunity occurs when antibodies
come form another source rather than from
the person’s own body.
 Example: Antibodies pass from the mothers
bloodstream to the fetus which temporarily
protects the fetus.
 Passive immunity usually lasts no more
than a few months.
The Body’s Defenses
Line of Defense
 Barriers such as the sin, breathing passages,
mouth, and stomach trap and kill pathogens.
 Skin – pathogens must get through a thick layer of
dead cells packed closely together.
 Breathing Passages – the respiratory system has
mucus and cilia that trap and remove most
 Mouth and Stomach – Saliva contains materials
that are destructive to pathogens and the stomach
contains acid which is deadly to pathogens.
Second Line of Defense
 The Inflammatory response
 When a person is cut, certain cells release a
chemical called histamine, which causes
blood vessels to dilate. In the Inflammatory
response, certain types of white blood cells
leave the blood vessels and move into
nearby tissues. The white blood cells then
fight the pathogens. Phagocytosis. You
also notice a red area around the cut
because of increased blood flow to the area.
Inflammatory Response
Line of Defense
 If a pathogen infection is severe enough to
cause a fever, it triggers a immune response.
 Your immune response is mainly conducted
by WBC’s called lymphocytes.
 There are two types of lymphocytes. They
are B cells and T cells.
Third Line of Defense ( The Immune System)
 B Cells produce
antibodies that are
used to fight
T Cells
 T cells directly
attack host cells
that contain
bacteria or viruses.
Aids, A disease of the Immune System
 Acquired Immunodeficiency Syndrome, or
AIDS is a disease caused by a virus that
attacks the immune system.
How HIV Affects the
 HIV is the only kind of virus known to
attack the immune system directly.
Once it invades the Body, HIV enters
T cells and reproduces inside them.
 NOTE ( People can be infected with
HIV for years before they become sick.
How HIV Is Spread
HIV can spread from one person to another only if body
fluids from an infected person comes in contact with those
of an uninfected person.
Sexual contact is one way in which this can happen.
HIV may also pass from an infected woman to her baby
during pregnancy or childbirth or through breast milk.
When drug users share needles, some infected blood may
get into the needle and then infect the next person who
uses it.
A person can also get HIV through a blood transfusion of
blood that contains the virus..
Ways HIV is not spread
It does not live on skin.
 You can’t get infected by using a
toilet seat after it has been used by
someone with HIV.
 HIV is not spread when you bump
into someone while playing sports.
 How Does HIV affect the body?
 Answer- It attacks the immune system directly.
HIV enters the T cells and reproduces.
 How is HIV spread?
 1. From one person to another only if body fluids
from an infected person comes in contact with
those of an uninfected person.
 2. Sexual contact.
 3. From and infected woman to her baby during
 4. From drug users sharing needles.
 5. Through a blood transfusion.