Transcript Chapter 19-3: Diseases Caused by Bacteria and Viruses

Chapter 19-3: Diseases Caused
by Bacteria and Viruses
• Bacteria and viruses
are everywhere in
nature, but only a
few cause disease.
• Disease-causing
agents are called
pathogens.
Bacterial Disease in Humans
• Many bacteria live on
and within our
bodies.
• Growth of pathogenic
bacteria disrupts the
body’s equilibrium by
interfering with its
normal activities and
producing disease.
How do bacteria cause disease?
1. They damage the cells and
tissues of the infected
organism directly by
breaking down the cells for
food.
2. Or they release toxins
(poisons) that travel
throughout the body
interfering with the normal
activity of the host.
Preventing Bacterial Disease
• Many bacterial diseases
can be prevented by
vaccines (a preparation
of weakened or killed
pathogens).
• When injected into the
body, a vaccine may
prompt the body’s
immunity to the disease.
Treating Bacterial Disease
• If infection occurs, drugs
can be used to destroy
bacteria.
• These drugs include
antibiotics, which are
compounds that block the
growth and reproduction of
bacteria.
• A reason for increased
human life expectancy is an
increased understanding of
how to prevent and cure
bacterial infections.
Viral Disease in Humans
• Viruses produce disease by disrupting the
body's normal equilibrium.
• How do viruses cause disease?
1. Lytic: viruses can attack
and destroy certain cells in
the body, causing
symptoms of the disease.
2. Lysogenic: other viruses
cause infected cells to
change patterns of growth
and development.
Viral Disease Prevention/Treatment
• Vaccines are the best
protection against viral
diseases, but only work if
used before an infection
begins.
• Viral diseases cannot be
treated with antibiotics.
• Symptoms may be treated
with over-the-counter
medicines.
Bacterial Diseases
Viral Diseases
• Lyme disease
• Common cold
• Tetanus
• Influenza
• Tuberculosis
• AIDS
• Bacterial meningitis
• Chicken pox
• Strep throat
• Hepatitis B
• West Nile
40-1: Infectious Disease
• Disease: any change,
other than an injury, that
disrupts the normal
function of the body
o Can be inherited, caused
by materials in the
environment, or produced
by pathogens (disease
causing agents).
The Germ Theory of Disease
• Idea that infectious
diseases are caused by
microorganisms, or
germs
• Observed by French
chemist Louis Pasteur
and German
bacteriologist Robert
Koch
Koch’s Postulates
• Series of guidelines used
to identify the
microorganism that
causes a specific disease
• These rules are important
because identifying
pathogens that cause
disease is the first step
toward prevention or
cures.
The Postulates (or rules)
1. The pathogen should always be found in a
sick organism, not a healthy one.
2. It must be isolated and grown in the lab.
3. When injected in a new host, it should cause
the same original disease.
4. The injected pathogen should be isolated
from the new host and identical to the
original pathogen.
Agents of Disease
• For many pathogens, the human body
provides just the right conditions for growth.
Agent
Example
Viruses
Common cold, flu, warts
Bacteria
Botulism, Anthrax
Protists
Malaria, African Sleeping Sickness
Worms
Schistosoma
Fungi
Athletes foot, ringworm
Fungi: athlete's foot
How Diseases Are Spread
• Coughing, sneezing,
or physical contact
• Contaminated food
or water
• Vectors: infected
animals that carry
pathogens from
person to person
Fighting Infectious Diseases
• Antibiotics: compound that blocks the growth
and reproduction of bacteria (no effect on
viruses)
• Over-the-Counter Drugs: treat only the
symptoms, but do not actually treat the cause
of the infection
40-2: The Immune System
• The body's main defense
against pathogens.
• It fights infection by
producing cells that
inactivate foreign
substances or cells.
• This process is called
immunity.
• Includes two
general categories
of defense
mechanisms
against infection:
o nonspecific defenses
o specific defenses
Nonspecific Defenses
• Nonspecific defenses
do not discriminate
between one threat
and another.
• There are two lines of
defense:
o First Line of Defense
o Second Line of Defense
First Line of Defense
• Skin: most important,
physical barrier
• Mucus, sweat, and
tears: contain the
enzyme lysozyme
which breaks down
the cell walls of
bacteria
• Oil and sweat glands in
the skin produce an
acidic environment that
kills many bacteria.
• Other examples:
o Cilia in the nose and
throat push
pathogens away from
the lungs.
o Stomach acid and
digestive enzymes
destroy pathogens.
Second Line of Defense
• If pathogens do enter the
body (get past the first line
of defense), the
inflammatory response is
activated.
• The inflammatory response
is a nonspecific defense
reaction to tissue damage
caused by injury or infection.
• Symptoms of inflammation:
redness, swelling, heat, pain
The Inflammatory Response
• When pathogens are
detected, the immune system
makes white blood cells,
which fight the infection.
• Blood vessels near the wound
expand, and white blood cells
move from the vessels to
enter the infected tissues.
• Many are phagocytes
(macrophages, neutrophils,
monocytes, eosinophils),
which engulf and destroy
bacteria.
• The infected tissue may
become swollen and painful.
• The immune system
releases chemicals that
increase the core body
temperature, causing a
fever.
o This high temperature
slows or stops the
growth of pathogens.
o It also increases heart
rate so white blood cells
get to the site of
infection faster.
Interferon
• Sometimes, virus-infected cells produce proteins
that help other cells resist viral infection.
• These proteins are named interferons because
they “interfere” with the growth of the virus.
• They inhibit synthesis of viral proteins in infected
cells and help block viral replication.
• This process slows the progress of infection and
gives the specific defenses of the immune system
time to respond.
Specific Defenses
• If a pathogen gets past
the nonspecific
defenses, the immune
system reacts with a
series of specific
defenses called the
immune response.
• Any substance, such as a
virus or bacterium, that
triggers this response is
known as an antigen.
The cells of the immune system
(lymphocytes) that recognize specific
antigens are:
B lymphocytes (B cells)
• Made in Bone marrow
T lymphocytes (T cells)
• Mature in the Thymus gland
Humoral (Antibody) Immunity
• Humoral immunity
produces antibodies.
• An antibody is a
protein that
recognizes and binds
to an antigen.
• An antibody is shaped
like the letter “Y” and
has two identical
antigen-binding sites.
Humoral (Antibody) Immunity
B
Cell-Mediated Immunity
• Cell-mediated immunity is the response
against abnormal cells (ex: cancer) and
pathogens.
• When viruses or other pathogens get inside
living cells, antibodies alone cannot destroy
them.
• In cell-mediated immunity,
T cells divide and
differentiate into different
types:
o Killer T cells destroy
infected cells by
secreting perforin,
creating lesions in the
cell that cause cell
death (apoptosis).
o Helper T cells produce
memory T cells.
o Suppressor T cells shut
down killer T cells
when done.
o Memory T cells cause
secondary response.
Cell-Mediated Immunity
Transplants
• Killer T cells make organ
transplants difficult.
• The immune system would
recognize a transported organ
as foreign (antigens) and attack
it. This is known as organ
rejection.
• To prevent this, doctors find a
donor whose cell markers are
nearly identical to cell markers
of the recipient.
• Recipients must take drugs to
suppress the cell-mediated
immune response.
Acquired Immunity
• Edward Jenner –
history of smallpox
vaccination
Active Immunity
• Injection of a weakened or
mild form of a pathogen to
produce immunity is known
as a vaccination.
• Vaccines stimulate the
immune system to create
millions of plasma cells
ready to produce specific
types of antibodies.
• Immunity produced by the
body's reaction to a vaccine
is known as active
immunity.
• Active immunity may
develop:
o after exposure to an
antigen (fighting an
infection).
o from deliberate
exposure to an antigen
(vaccine).
• Today, over 20 serious
human diseases can
be prevented by
vaccination.
Passive Immunity
• The body can also be temporarily protected
against disease.
• If antibodies produced by other animals are
injected into the bloodstream, the antibodies
produce a passive immunity.
• Passive immunity is temporary because
eventually the body destroys the foreign
antibodies.
• Passive immunity may
develop:
o Naturally when antibodies
produced by the mother
are passed to the fetus
during development or in
early infancy through
breast milk.
o Deliberately when
antibodies are
administered to fight
infection or prevent disease
(ex: rabies antibodies,
snake bite serum)