Download An Introduction to the Viruses Chapter 6 Part 3

An Introduction
to the Viruses
Chapter 6
Part 3
Copyright © The McGraw-Hill Companies, Inc) Permission required for reproduction or display.
Damage to the Host Cell and
Persistent Infections
• Cytopathic effects- virus-induced damage to the
cell that alters its microscopic appearance
• Inclusion bodies- compacted masses of
viruses or damaged cell organelles
• Synctia- fusion of cells
• Latent infections
• Tranformation – oncogenic, cancer causing
(oncoviruses)
Cytopathic Effects
Results of Viral Infections- Examples
• Death of host cell = Most viruses
• Proliferation of cells = Papillomavirus
• Fusion of host cells = Respiratory syncytial virus
• Transformation of cells = Adenovirus
• No obvious changes = Rubella
Viruses that Infect Bacteria
• Bacteriophage
• Most contain dsDNA
• Often make the bacteria they infect more
pathogenic for humans
• Some are named “T-even phages”, such as T2
and T4
• Attach, but do not enter host bacterial cell
T-even Bacteriophages
• Icosahedral capsid head
containing DNA
• Central tube surrounded
by a sheath
• Collar
• Base plate
• Tail pins and fibers
• Inject nucleic acid into
bacterial cell
Bacteriophages
• Entry of the nucleic acid
causes the cessation of
host cell DNA replication
and protein synthesis
• The host cell machinery
is then used for viral
replication and synthesis
of viral proteins
• As the host cell
produces new parts,
they spontaneously
assemble
• Eventually host cell
lyses
Lysogeny: The Silent Virus Infection
• Temperate phages- special DNA phages that undergo
adsorption and penetration but are not replicated or
released immediately
• Instead the viral DNA enters an inactive prophage stage
• Lysogeny: the cell’s progeny will also have the
temperate phage DNA
• Lysogenic conversion: when a bacterium acquires a
new trait from its temperate phage
Lytic and Lysogenic Cycles
Bacteriophage vs. Animal Virus
Multiplication
Concept Check
Corynebacterium diphtheriae becomes more
pathogenic when a bacteriophage called beta is
incorporated into its genome. What is this process
called?
A. Transposition
B. Transformation
C. Lysogenic conversion
D. Lytic cycle
Concept Check
How are the infectious cycles of viruses different in
bacterial and eukaryotic host cells?
A. The virus genome does not enter a
eukaryote.
B. The virus genome does not enter a
bacterium.
C. The capsid does not enter a eukaryote.
D. The capsid does not enter a bacterium.
6.6 Techniques in Cultivating and
Identifying Animal Viruses
• Primary purposes of viral cultivation
• To isolate and identify viruses in clinical specimens
• To prepare viruses for vaccines
• To do detailed research on viral structure,
multiplication cycles, genetics, and effects on host
cells
• Using Live Animal Inoculation
• Specially bred strains of white mice, rats, hamsters,
guinea pigs, and rabbits
• Occasionally invertebrates or nonhuman primates are
used
• Animal is exposed to the virus by injection
Viral Culture
• Using Bird Embryos
• Enclosed in an eggnearly perfect
conditions for viral
propagation
• Chicken, duck, and
turkey are most
common
• Egg is injected through
the shell using sterile
techniques
Using Cell (Tissue) Culture
Techniques
• Most viruses are propagated in some sort of cell
culture
• The cultures must be developed and maintained
• Animal cell cultures are grown in sterile
chambers with special media
• Cultured cells grow in the form of a monolayer
• Primary or continuous
Detecting Viruses in the Lab
• Plaque assays (used
to visualize the
presence of virus)
• Bacteria cultures used
for bacteriophage
• Tissue culture used for
eukaryotes
6.7 Medical Importance of Viruses
• Infectious diseases
• Chronic affliction association
• Type I diabetes, multiple sclerosis
• Cancer
6.8 Noncellular Infectious Agents
• Viroids
• Plant pathogens
• Naked RNA, Single-stranded, Circles, Very small (100
to 300 nucleotides)
• Prions
• Animal pathogens, “Slow viruses”
• Spongiform encephalopathy
• Mad Cow Disease, Creutzfeld-Jakob Disease
• Defectively folded host protein