PHAR 2101 Clin. Micro. Intro. to Virology slides

8/7/2019 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

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PHAR 2101 Clin. Micro. Intro. to Virology slides