Download Viruses, bacteria, viroids, and prions can all cause infection.

Viruses, bacteria, viroids, and prions can all
cause infection.
Any disease-causing agent is called a pathogen.
1 nanometer (nm) = one
billionth of a meter
100 nm
eukaryotics cells
10,000-100,000 nm
prokaryotic cells
200-10,000 nm
viruses
50-200 nm
viroids
5-150 nm
prion
2-10 nm
A prion is made only of proteins.
- causes misfolding of
other proteins
- results in diseases of
the brain
A viroid is made only of single-stranded RNA.
– causes disease in plants
– passed through seeds or pollen
Viruses differ in shape, genetic material,
and in ways of entering host cells.
– non-living pathogen
– can infect many organisms
• Viruses have a simple structure.
– genetic material (either DNA or RNA)
– capsid, a protein shell
– maybe a lipid envelope, a protective outer coat
Viral Shapes: depends
on proteins of capsid
enveloped
(influenza)
capsid
helical
(rabies)
nucleic acid
lipid
envelope
surface
proteins
capsid
polyhedral
(foot-and-mouth
disease)
Surface proteins
nucleic
acid
lipid
envelope
surface
proteins
capsid
nucleic acid
Bacteriophage: A type of virus that prey
exclusively on bacteria. Viral DNA is injected
into bacteria cell.
A bacteriophage is a virus that infects a
bacterium.
capsid
HEAD
DNA
collar
tail sheath
TAIL
Base
plate
tail fiber
Plant Phages: Prey exclusively on seed plants
Tobacco Mosaic Virus
Animal Phages: Prey exclusively on
animals.
The Influenza Virus
Viruses enter cells in various ways.
– bacteriophages pierce host cells
– viruses of eukaryotes enter by endocytosis or fuse
with the membrane
LYTIC
CYCLE
Bacteriophage lytic cycle
Attachment
Assembly & Lysis
(release)
Are released viruses
genetically the same
as the original virus?
Lysogenic
ticking time bomb
2 possible results
1) after cell divisions,
lytic cycle kicks in or
2) viruses escape via
budding, using host’s
cell membrane;
leaving host intact,
but weakened.
 Host- the cell the virus is infecting
 Lysogenic bacteria- a bacterium that
has a piece of the viral DNA embedded
in its own DNA (has a prophage)
 Prophage (provirus)- segment of viral
DNA that is integrated in the host’s
DNA
 Cell Multiplication- host cell is
dividing and dividing, all the while
making copies of the viral nucleic acid
Differences between Lytic and Lysogenic
Cycles:
Lytic Cycle
Lysogenic Cycle
Viruses cause many
infectious diseases
There are many
examples of
viral infections.
- common cold
Viruses cause many
infectious diseases
There are many
examples of
viral infections.
-
common cold
influenza
Viruses cause many
infectious diseases
There are many
examples of
viral infections.
-
common cold
influenza
SARS
Viruses cause many
infectious diseases
There are many
examples of viral
infections.
-
common cold
influenza
SARS
HIV-infected white blood cell
HIV
- The body has natural
defenses against
viruses.
How Viruses Change
 Viruses can mutate when they copy the
genetic material
 Copy something wrong
 Mistake may prove useful
 More “fit” virus (more infections)
Some viral
diseases can
be prevented
with
vaccines.
Vaccines are made from weakened
pathogens.
 A vaccine stimulates the body’s own immune response.
 Vaccines prepare the immune system for a future attack.
•
Vaccines are the only way to control the spread of viral disease.
Immunity
- achieved through presence of antibodies
Antibodies

Proteins produced by the body to neutralize or
destroy toxins OR disease carrying agents

Disease specific!!!
Antigen

Any foreign substance in the body that triggers
production of antibodies

Allergen, bacteria, virus, etc.
Types of Immunity
Active Immunity



Long lasting, sometimes lifetime
Usually takes several weeks to develop
Exposure to disease organism triggers antibodies to be made


Natural immunity: infection with the disease
Vaccine-induced: exposure to the weakened or killed form
Passive Immunity



Only lasts a few weeks or month
Protection is immediate
Person is given antibodies rather than producing them on their own


Newborn baby: from mother to placenta or through breastmilk
Blood products: receiving blood with antibodies
How are viruses transmitted?
Depends on the type of virus, but these are common ways:
• Airborne/aerosol
• Contaminated food/water
• Vectors (infected animal bite)
• Sexual contact
• Contaminated blood products/transfusions
• Other bodily fluids
• Breast milk
• Exposure at birth