phar 2101 clin. micro. intro. to virology slides
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Chapter 13: Viruses
Viruses contain DNA or RNA
And a protein coat,
Some are enclosed by an envelope
May have spikes protruding from envelope
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Most viruses infect only specific types of cells in onehost
Host range is determined by specific host attachmentsites and cellular factors
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Viruses
Figure 13.1
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Polyhedral Viruses
Figure 13.2a, b
Causes human respiratory
and gastrointestinal diseases
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Helical Viruses
Figure 13.4a, b
Causes systemic infection often
with hemorrhagic fever
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Complex Viruses
Figure 13.5a
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Viral Taxonomy
Family names end in -viridae
Genus names end in -virus
A group of viruses sharing the same genes andecological niche (host). Common names are used forspecies
Subspecies are designated by a number
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Viral Taxonomy
Family : Herpesviridae
Genus: Simplexvirus
Species/Subspecies: Human herpes virus 1,HHV 2, HHV 3
Family: Retroviridae
Genus: Lentivirus
Species/Subspecies: Human
Immunodeficiency Virus 1, HIV 2
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Growing Viruses Viruses must be
grown in living
cells.
infect bacteria,and form plaques
on a lawn ofbacteria.
Figure 13.6
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Growing Viruses
Animal viruses may
be grown in living animals
In embryonatedeggs
or in cell culture.
Figure 13.7
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Growing Viruses
Animal (and plant) viruses may be grown in
Continuous cell lines may be maintained
indefinitely.
Figure 13.8
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I.e. inclusion bodies in cells infected with the rabiesvirus
Serological tests
Detect antibodies against viruses in a patient
Use antibodies to identify viruses
Western blot
Viral nucleic acids: RFLPs, PCR
Virus Identification
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Virus Identification a cytopathic effect
Figure 13.9
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Viruses require host cell machinery for replication
Some viruses have some of their own enzymes: mainly
for viral nucleic acid replication
Most, if not all, enzymes come from host cell
These enzymes are involved in building new virions
Viral Multiplication
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Phage causes lysis and death ofhost cell
Attachment Phage attaches by tail fibers tohost cell
Penetration Phage lysozyme opens cell wall;DNA is then injected into cell
Biosynthesis Production of phage DNAand proteins
Maturation Assembly of phage particles Release Phage lysozyme breaks cell wall
Multiplication of Bacteriophages (Lytic Cycle)
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Figure 13.10.1
Attachment:Phage attachesto host cell.
Penetration:Phage penetrateshost cell andinjects its DNA.
Biosynthesis:phage DNA directssynthesis of viralcomponents byhost cell.
1
2
3
Bacterialcell wall
Bacterialchromosome
Capsid DNA
Capsid
Sheath
Tail fiber
Base plate
Pin
Cell wall
Tail
Plasma membrane
Sheath contracted
Tail core
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Figure 13.10.2
4 Maturation:Viral componentsare assembled intovirions.
Tail
5 Release:Host cell lyses andnew virions arereleased.
DNA
Capsid
Tail fibers
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The Lysogenic Cycle: Phage DNA incorporated into host DNA
Figure 13.12
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Specialized Transduction
Figure 13.13
Prophage exists in galactose-using host(containing the galgene).
Phage genome excises, carryingwith it the adjacent galgene fromthe host.
Phage matures and cell lyses, releasingphage carrying galgene.
1
2
3
Prophage
galgene
galgene Bacterial DNA
Galactose-positivedonor cell galgene
Phage infects a cell that cannot utilizegalactose (lacking galgene).
4
Galactose-negativerecipient cell
Along with the prophage, the bacterial galgene becomes integrated into the newhosts DNA.
5
Lysogenic cell can now metabolizegalactose.
6
Galactose-positive recombinant cell
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Attachment Viruses attach 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 proteinsassemble
Release By budding (enveloped viruses) or
rupture
Multiplication of Animal viruses
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Attachment, Penetration, and Uncoating
Figure 13.14
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Release of an enveloped virus by budding
Figure 13.20
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Nonenveloped DNA virus
Can cause cancer (cervical cancer)
Hand warts
Genital warts
Sexually transmitted
Respiratory infections in humans Usually sudden onset and short duration
Tumors in animals
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nveloped DNA virus
Can cause chronic liver disease
Can lead to liver cancer
Body fluid transmisson
Human Herpes Virus 1 and HHV 2 cold sores andgenital herpes
Sexually transmitted
Other direct contact transmission
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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Enveloped DNA virus Varicella-Zoster virus (HHV 3)
Chicken pox is initial infection
Shingles may occur later
Contracted by inhaling virus
Epstein-Barr virus (HHV 4) Infectious Mononucleosis
Saliva transmission
Burkitts lymphoma in African children
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Multiplication of a Retrovirus
Figure 13.19
Retrovirus penetrateshost cell.
Its RNA isuncoated; reversetranscription takesplace.
The new viral DNA istranported into the host cellsnucleus and integrated as aprovirus. The provirus maydivide indefinitely with thehost cell DNA.
1
2
3
Envelope
Transcription of theprovirus may also occur,producing RNA for newretrovirus genomes andRNA that codes for theretrovirus capsid andenvelope proteins.
4
Matureretrovirusleaves host
cell, acquiringan envelope asit buds out.
5
CapsidReversetranscriptase
Virus Two identical strands of RNA
DNA of one of the hostcells chromosomes
Provirus
Hostcell
Reverse
transcriptase
Viral RNA
RNA
Viral proteins
Identicalstrands ofRNA
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Use reverse transcriptase to produce DNA from RNA
viral genome
HIV - AIDS
Oncogenic viruses
Some retroviruses can cause cancer
Retroviruses enveloped RNA viruses
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The genetic material of oncogenic viruses becomes
integrated into the host cell's DNA.
transform normal cells into
cancerous cells.
An oncovirus can promote oncogene expression
may contain oncogenes
Cancer
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Virus remains in host cell for long periods,asymptomatically
Subsequent activation may lead to: i.e. coldsores, shingles
Persistent Viral Infections
Disease progresses over a long period, generally
fatal Subacute sclerosing panencephalitis, SSPE
(measles virus)
AIDS dementia complex (HIV)
Viral Infections
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Infectious proteins
Inherited, and transmissible by ingestion, transplant, &surgical instruments
Spongiform encephalopathies (fatal): Sheep Scrapie,Creutzfeldt-Jakob disease, mad cow disease
Cause:
normal cellular prion protein on cellsurface,
converts to
scrapie protein, accumulates in braincells forming plaques
Prions
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Prions
Figure 13.21
PrPc
PrPSc
1 2 3 4
5 6 7 8
Endosome
Lysosome
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Figure 13.22
Plant Viruses
enter throughwounds or viainsects
areinfectious RNA
One causes
potato spindletuber disease
Plant viruses and viroids
PotatoSpindle Tuber Viroids
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RNA virus, nonenveloped
Poliovirus
May be paralytic in ~1% of cases Transmission:
Human Number one cause of the common cold
Hepatitis A virus
Attacks liver, kidneys, spleen
Transmission: fecal-oral route
Usually not fatal
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Influenza viruses A, B, and C
Type A have caused
Both type A and B cause the Flu
Subtypes differ based on H and N spike variation
Mutation of H and N spike can lead to epidemicsor pandemics
RNA virus, enveloped
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Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings
RNA virus, enveloped
Infects birds and humans
Transmitted by mosquitos
First appeared in U.S. in 1999 in NYC area; nowcoast to coast
Can be fatal