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TORTORA • FUNKE
• CASE
Microbiology
AN INTRODUCTION
EIGHTH EDITION
B.E Pruitt & Jane J. Stein
Chapter 13, part B
Viruses, Viroids, and Prions
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
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Attachment, Penetration, and Uncoating
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Figure 13.14
Release of an enveloped virus by budding
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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
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3 Early transcription and
translation; enzymes are
synthesized
Figure 13.15
Pathways of Multiplication for RNA-Containing Viruses
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Figure 13.17
Multiplication of a Retrovirus
Capsid
Reverse
transcriptase
DNA
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.
Reverse
transcriptase
Viral RNA
Identical
strands of
RNA
2 Virion penetrates
cell and its DNA is
uncoated
4 Transcription of the
Viral proteins
RNA
provirus may also occur,
producing RNA for new
retrovirus genomes and
RNA that codes for the
retrovirus capsid and
envelope proteins.
Provirus
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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
• 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.
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Oncogenic Viruses
• Oncogenic DNA Viruses
• Adenoviridae
• Oncogenic RNA viruses
• Retroviridae
• Papovaviridae
• Viral RNA is
transcribed to DNA
which can integrate
into host DNA
• Hepadnaviridae
• HTLV 1
• Heresviridae
• Poxviridae
• HTLV 2
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• Latent Viral Infections
• Virus remains in asymptomatic host cell for long
periods
• Cold sores, shingles
• Persistent Viral Infections
• Disease processes occurs over a long period,
generally fatal
• Subacute sclerosing panencephalitis (measles
virus)
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Prions
• Infectious proteins
• Inherited and transmissible by ingestion, transplant, &
surgical instruments
• Spongiform encephalopathies: Sheep scrapie,
Creutzfeldt-Jakob disease, Gerstmann-SträusslerScheinker syndrome, fatal familial insomnia, mad cow
disease
• PrPC, normal cellular prion protein, on cell surface
• PrPSc, scrapie protein, accumulate in brain cells
forming plaques
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Prions
PrPSc
PrPc
1
2
3
4
Lysosome
Endosome
5
6
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7
8
Figure 13.21
• Plant Viruses
• Plant viruses
enter through
wounds or via
insects
• Viroids
• Viroids are
infectious
RNA; potato
spindle tuber
disease
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Figure 13.22
Some Plant Viruses
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Table 13.6
Virus Families
• Single-stranded DNA,
nonenveloped viruses
• Parvoviridae
• Human parvovirus
• Fifth disease
• Anemia in
immunocompromised
patients
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Double-stranded DNA, nonenveloped viruses
• Mastadenovirus
• Respiratory
infections in
humans
• Tumors in animals
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Double-stranded DNA, nonenveloped viruses
• Papillomavirus
(human wart virus)
• Polyomavirus
• Cause tumors,
some cause
cancer
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Double-stranded DNA, nonenveloped viruses
• Orthopoxvirus
(vaccinia and
smallpox viruses)
• Molluscipoxvirus
• Smallpox,
molluscum
contagiosum,
cowpox
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Double-stranded DNA, nonenveloped viruses
• Simplexvirus (HHV1 and HHV
2)
• Varicellavirus (HHV 3)
• Lymphocryptovirus (HHV 4)
• Cytomegalovirus (HHV 5)
• Roseolovirus (HHV 6)
• HHV 7
• Kaposi's sarcoma (HHV 8)
• Some herpesviruses can
remain latent in host cells
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Double-stranded DNA, nonenveloped viruses
• Hepadnavirus
(Hepatitis B virus)
• Use reverse
transcriptase to
produce DNA from
mRNA
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Single-stranded RNA, + strand, nonenveloped
• Enterovirus
• Enteroviruses
include poliovirus
and coxsackievirus
• Rhinovirus
• Hepatitis A virus
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Single-stranded RNA, + strand, nonenveloped
• Hepatitis E virus
• Norovirus (Norwalk
agent) causes
gastroenteritis
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Single-stranded RNA, + strand, nonenveloped
• Alphavirus
• Alphaviruses are
transmitted by
arthropods;
include EEE, WEE
• Rubivirus (rubella
virus)
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Single-stranded RNA, + strand, nonenveloped
• Arboviruses can replicate
in arthropods; include
yellow fever, dengue, SLE,
and West Nile viruses
• Hepatitis C virus
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Single-stranded RNA, + strand, nonenveloped
• Coronavirus
• Upper respiratory
infections
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Single-stranded RNA, – strand, one RNA strand
• Vesiculovirus
• Lyssavirus (rabies
virus)
• Cause numerous
animal diseases
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Single-stranded RNA, – strand, one RNA strand
• Filovirus
• Enveloped,
helical viruses
• Ebola and
Marburg viruses
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Single-stranded RNA, – strand, one RNA strand
• Paramyxovirus
• Morbillivirus
• Paramyxovirus
causes
parainfluenza,
mumps and
Newcastle disease
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Single-stranded RNA, – strand, one RNA strand
• Hepatitis D virus
• Depends on
coinfection with
Hepadnavirus
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Single-stranded RNA, –
strand, multiple RNA strands
• Influenzavirus
(Influenza viruses A
and B)
• Influenza C virus
• Envelope spikes
can agglutinate
RBCs
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Single-stranded RNA, –
strand, multiple RNA strands
• Bunyavirus (CE virus)
• Hantavirus
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Single-stranded RNA, –
strand, multiple RNA strands
• Arenavirus
• Helical capsids
contain RNAcontaining
granules
• Lymphocytic
choriomeningitis
• VEE and Lassa
Fever
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Single-stranded RNA, two RNA strands,
produce DNA
• Lentivirus (HIV)
• Oncogenic viruses
• Use reverse
transcriptase to
produce DNA from
viral genome
• Includes all RNA
tumor viruses
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Double-stranded RNA, nonenveloped
• Reovirus (Respiratory
Enteric Orphan)
• Rotavirus
• Mild respiratory
infections and
gastroenteritis
• Colorado tick fever
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