Download Viruses, Viroids, and Prions

Viruses, Viroids, and
Prions
Bits and Pieces that cause
disease
Viruses
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Viruses contain DNA or RNA and a
protein coat
Some are enclosed by an envelope
Some viruses have spikes
Most viruses infect only specific
types of cells in one host
Host range is determined by
specific host attachment sites and
cellular factors
Viruses
Figure 13.1
Helical Viruses
Figure 13.4a, b
Polyhedral Viruses
Figure 13.2a, b
Complex Viruses
Figure 13.5a
Viral Taxonomy
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Family names end in -viridae
Genus names end in -virus
Viral species: A group of viruses sharing
the same genetic information and
ecological niche (host). Common names are
used for species
Subspecies are designated by a number
Viral Taxonomy

Herpesviridae

Herpesvirus
Human herpes virus 1
 HHV 2
 HHV 3
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Retroviridae

Lentivirus
Human Immunodeficiency Virus 1
 HIV 2
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Growing Viruses
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Viruses must be
grown in living
cells.
Bacteriophages
form plaques on
a lawn of
bacteria.

Figure 13.6
Growing Viruses

Animal
viruses may
be grown in
living animals
or in
embryonated
eggs.
Figure 13.7
Growing Viruses
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Animal and plants viruses may be grown
in cell culture.

Continuous cell lines may be maintained
indefinitely.
Figure 13.8
Virus Identification
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Cytopathic effects
Serological tests
Detect antibodies against viruses in a patient
 Use antibodies to identify viruses in
neutralization tests, viral hemagglutination,
and Western blot

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Nucleic acids
RFLPs
 PCR
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Virus Identification
Figure 13.9
Bacterial
cell wall
Bacterial
chromosome
Capsid
DNA
Capsid
Sheath
Tail fiber
1 Attachment:
Phage attaches
to host cell.
Base plate
Pin
Cell wall
Tail
Plasma membrane
2 Penetration:
Phage pnetrates
host cell and
injects its DNA.
Sheath contracted
Tail core
3 Merozoites released
into bloodsteam
from liver may
infect new red
blood cells
Figure 13.10.1
Tail
DNA
4 Maturation:
Viral components
are assembled into
virions.
Capsid
5 Release:
Host cell lyses and
new virions are
released.
Tail fibers
Figure 13.10.2
Multiplication of
Bacteriophages (Lytic Cycle)
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Attachment
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Penetration
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Biosynthesis
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Maturation
Release
Phage attaches by tail fibers to
host cell
Phage lysozyme opens cell wall,
tail sheath contracts to force tail
core and DNA into cell
Production of phage DNA
and proteins
Assembly of phage particles
Phage lysozyme breaks cell wall
One-step Growth Curve
Figure 13.11
The Lysogenic Cycle
Figure 13.12
Lytic vs Lysogenic
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Lytic cycl3
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Phage causes lysis and death of
host cell
Lysogenic cycle
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Prophage DNA incorporated in
host DNA
Specialized Transduction
Prophage
gal gene
Bacterial DNA
1 Prophage exists in galactose-using host
(containing the gal gene).
gal gene
Galactose-positive donor cell
gal gene
Galactose-negative
recipient cell
2 Phage genome excises, carrying
with it the adjacent gal gene from
the host.
3 Phage matures and cell lyses, releasing
phage carrying gal gene.
4 Phage infects a cell that cannot utilize
galactose (lacking gal gene).
5 Along with the prophage, the bacterial gal
gene becomes integrated into the new
host’s DNA.
Galactose-positive recombinant cell
6 Lysogenic cell can now metabolize
galactose.
Figure 13.13
Multiplication of Animal
viruses
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Attachment
Viruses attaches to cell
membrane
Penetration By endocytosis or fusion
Uncoating
By viral or host enzymes
Biosynthesis Production of nucleic acid and
proteins
Maturation
Nucleic acid and capsid proteins
assemble
Release
By budding (enveloped viruses) or
rupture
Attachment, Penetration,
and Uncoating
Figure 13.14
Release of an enveloped virus by
budding
Figure 13.20
Multiplication of DNA Virus
Papovavirus
1 Virion attaches to host cell
7 Virions are released
Host cell
DNA
Capsid
DNA
2 Virion penetrates
cell and its DNA is
uncoated
Cytoplasm
6 Virions mature
Capsid proteins
mRNA
5 Late translation;
capsid proteins
are synthesized
4 Late transcription;
DNA is replicated
3 Early transcription and
translation; enzymes are
synthesized
Figure 13.15
Pathways of Multiplication for
RNA-Containing Viruses
Figure 13.17
Multiplication of a Retrovirus
Reverse
Capsid DNA
transcriptase
Virus
Two identical + stands of RNA
1 Retrovirus penetrates
host cell.
Host
cell
DNA of one of the host
cell’s chromosomes
5 Mature
retrovirus
leaves host
cell, acquiring
an envelope as
it buds out.
Viral RNA
Identical
strands of
RNA
4
Viral proteins
RNA
Reverse
transcriptase
Transcription of the
provirus may also occur,
producing RNA for new
retrovirus genomes and
RNA that codes for the
retrovirus capsid and
envelope proteins.
Provirus
2 Virion penetrates
cell and its DNA is
uncoated
3 The new viral DNA is
tranported into the host cell’s
nucleus and integrated as a
provirus. The provirus may
divide indefinitely with the
host cell DNA.
Figure 13.19
Cancer
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Activated oncogenes transform normal
cells into cancerous cells.
Transformed cells have increased growth,
loss of contact inhibition, tumor specific
transplant and T antigens.
The genetic material of oncogenic viruses
becomes integrated into the host cell's
DNA.
Oncogenic Viruses
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Oncogenic DNA
Viruses
Adenoviridae
 Heresviridae
 Poxviridae
 Papovaviridae
 Hepadnaviridae
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Oncogenic RNA
viruses
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Retroviridae
Viral RNA is
transcribed to DNA
which can integrate
into host DNA
 HTLV 1
 HTLV 2
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Latent vs Persistent
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Latent Viral Infections
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Virus remains in asymptomatic host cell for
long periods
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Cold sores, shingles
Persistent Viral Infections
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Disease processes occurs over a long period,
generally fatal
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Subacute sclerosing panencephalitis (measles
virus)
Prions
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Infectious proteins
Inherited and transmissible by ingestion,
transplant, & surgical instruments
Spongiform encephalopathies: Sheep scrapie,
Creutzfeldt-Jakob disease, GerstmannSträussler-Scheinker syndrome, fatal familial
insomnia, mad cow disease
PrPC, normal cellular prion protein, on cell
surface
PrPSc, scrapie protein, accumulate in brain cells
forming plaques
Prions
PrPSc
PrPc
1
2
3
4
Lysosome
Endosome
5
6
7
8
Figure 13.21
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Plant Viruses
 Plant viruses
enter through
wounds or via
insects
Viroids
 Viroids are
infectious
RNA; potato
spindle tuber
disease
Figure 13.22
Some Plant Viruses
Table 13.6
Virus Families
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Single-stranded DNA,
nonenveloped viruses
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Parvoviridae
Human parvovirus
 Fifth disease
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Anemia in
immunocompromised
patients
Double-stranded DNA,
nonenveloped viruses
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Mastadenovirus
Respiratory
infections in
humans
 Tumors in
animals
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Double-stranded DNA,
nonenveloped viruses
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Papillomavirus
(human wart
virus)
Polyomavirus
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Cause tumors,
some cause
cancer
Double-stranded DNA,
nonenveloped viruses
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Orthopoxvirus
(vaccinia and
smallpox
viruses)
Molluscipoxvirus
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Smallpox,
molluscum
contagiosum,
cowpox
Double-stranded DNA,
nonenveloped viruses
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Simplexvirus (HHV1 and
HHV 2)
Varicellavirus (HHV 3)
Lymphocryptovirus (HHV 4)
Cytomegalovirus (HHV 5)
Roseolovirus (HHV 6)
HHV 7
Kaposi's sarcoma (HHV 8)
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Some herpesviruses can
remain latent in host cells
Double-stranded DNA,
nonenveloped viruses
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Hepadnavirus
(Hepatitis B
virus)
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Use reverse
transcriptase to
produce DNA
from mRNA
Single-stranded RNA, +
strand, nonenveloped
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Enterovirus
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Enteroviruses
include
poliovirus and
coxsackievirus
Rhinovirus
Hepatitis A
virus
Single-stranded RNA, +
strand, nonenveloped
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Hepatitis E virus
Norovirus
(Norwalk agent)
causes
gastroenteritis
Single-stranded RNA, +
strand, nonenveloped
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Alphavirus
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Alphaviruses are
transmitted by
arthropods;
include EEE,
WEE
Rubivirus
(rubella virus)
Single-stranded RNA, +
strand, nonenveloped
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Arboviruses can
replicate in
arthropods; include
yellow fever, dengue,
SLE, and West Nile
viruses
Hepatitis C virus
Single-stranded RNA, +
strand, nonenveloped
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Coronavirus
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Upper
respiratory
infections
Single-stranded RNA, –
strand, one RNA strand
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Vesiculovirus
Lyssavirus
(rabies virus)
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Cause numerous
animal diseases
Single-stranded RNA, –
strand, one RNA strand
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Filovirus
Enveloped,
helical viruses
 Ebola and
Marburg
viruses
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Single-stranded RNA, –
strand, one RNA strand
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Paramyxovirus
Morbillivirus
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Paramyxovirus
causes
parainfluenza,
mumps and
Newcastle
disease
Single-stranded RNA, –
strand, one RNA strand
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Hepatitis D
virus
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Depends on
coinfection with
Hepadnavirus
Single-stranded RNA, –
strand, multiple RNA strands
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Influenzavirus
(Influenza
viruses A and B)
Influenza C
virus
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Envelope spikes
can agglutinate
RBCs
Single-stranded RNA, –
strand, multiple RNA strands
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Bunyavirus (CE virus)
Hantavirus
Single-stranded RNA, –
strand, multiple RNA strands
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Arenavirus
Helical capsids
contain RNAcontaining
granules
 Lymphocytic
choriomeningitis
 VEE and Lassa
Fever
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Single-stranded RNA, two RNA strands,
produce DNA
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Lentivirus (HIV)
Oncogenic viruses
 Use reverse
transcriptase
to produce
DNA from viral
genome
 Includes all
RNA tumor
viruses
Double-stranded RNA,
nonenveloped
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Reovirus
(Respiratory
Enteric Orphan)
Rotavirus
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Mild respiratory
infections and
gastroenteritis
Colorado tick
fever