WEEK 5 Viruses 2nd year - 2013 2014 [وضع التوافق].pdf

8/10/2019 WEEK 5 Viruses 2nd year - 2013 2014 [ ].pdf

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Introduction to

AhmedSayedAbdelMoneim

Professor,MicrobiologyDepartment(Virology)

CollegeofMedicineandMedicinalSciences

TaifUniversitySaudiArabia

Selected Reading

cro o ogy c ar . arvey, ame a . ampe

Medical Microbiology (Introduction to infectious

diseases, Sherris)

Fundamental Virology (Fields)

Prof. Ahmed Sayed Abdel-Moneim


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Objectives To know the definition of the virus To know the components and the general functions of each

virus structure

Classification and nomenclature of viruses

To know how virus replicates inside the host cell

Types of virus infections and how virus infection could beprevented

Diagnosis of virus infection


VirusesViruses are obligate intracelluar parasites that are

meta o ca y nert outs e t e r osts.

They can multiply only in living cells.



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Virus: Structural components

1.Nucleic acid

2.Protein coat [capsid]

3.Envelope in some viruses only

Nucleocapsid


Viral Genomes

Nucleic Acid

Single Stranded Parvovirus

RNA

Double Stranded

Linear

Double Stranded

Sin le Stranded

Partial Double Stranded

Positive sense

Herpesviruses

Hepatitis B virus

Poliovirus

Segmented

Negative sense Measles

Influenzavirues (Negative sense)



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Viral CapsidIt coats the viral nucleic acid

Significance of capsid?

Protect nucleic acid

Attach to receptors on cells

Capsid proteins provides antigen to which the

mmune system react


Types of Capsid

Helical symmetry Icosahedral symmetry Mixed

Influnezaviruses Polioviruses Poxviruses



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Viral EnvelopeSome viruses ossess envelo e.

envelope

The envelope is cell integral part.

It consists of lipid bilayer [cellular origin ] studded by

viral epitopes [viral origin].

The envelope render viruses sensitive to lipid solvents.

Examples of enveloped viruses

Non enveloped viruses are called naked ones.


Virus multiplication (replication)

It includes the following:

(1) Virus Attachment or adsorption (2) Virus penetration and uncoating

(3) Virus multiplication (4) Virus Assembly

(5) Virus Release

All DNA viruses replicate in the nucleus of the host cell except poxvirused replicate incytoplasm


replicate in the nucleus.


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A) Virus attachment or adsorptiona o s on. an om movement an meet ng o v rus part c es an ost ce occurs

(b) Ionic attraction. Counter positive ions are needed.

(c) Receptor Binding:

Adsorption of the virus occurs to specific receptor sites on the surface of the susceptible

host cell is called (tropism).


B) Penetration and uncoatinga-Penetration of necked viruses:Endocytosis or phagocytosis. Through the endosome or the phaghocytic

vacuole.

Translocation. Viruses pass directly to inside the host cell without noticeable

changes in cell membrane as picorna viruses.

b-Penetration of enveloped viruses:

Endocytosis or phagocytosis.

Fusion to plasma membrane. Virons bind to cell surface receptors via a viral

epitope (surface protein).

Uncoating.It means liberation of viral genome inside the host cell with subsequent

expression of viral coding genes.


viruses are not found inside the cell.


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C) Virus multiplication

RNA viruses

All RNA viruses replicate inside the cytoplasm except retroviruses.

Single stranded RNA (+)sense non segmented

The genome acts as m RNA and translated directly in ribosomes.

Single stranded RNA (-)sense non segmented

It carries RNA dependent RNA polymerase (transcriptase) by which complementary positive strand (mRNA ) is

transcribed

Single stranded RNA (-)sense segmented

It carries RNA dependent RNA polymerase (transcriptase) by which complementary positive strand (mRNA ) is

transcribed for each segment

Single stranded RNA (+) sense segmented

Ex. retroviruses

reverse transcriptase: RNA to dsDNA

The resulted ds DNA is then integrate itself into host cell genome.

Segmented dsRNA

Ex. reovirus and birnaviruses


.

The mRNA molecules


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DNA viruses

All DNA viruses replicate inside the DNA except poxviruses

Parvovirus and hepadenavirus use reverse transcriptase enzyme




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Consequences of infection Productive: Production of progeny virus particles.

Abortive: Failure of infection

Latent:The viral nucleic acid persists in a dormant state in certain cells after the virus

shedding. e.g. herpes viruses. The virus is reactivated when the host is

stressed.

Transforming:

Transform normal cells to tumor ones e.g. Retroviruses

Persistent

In this form, the virus is continuously detected with mild or no clinicalsymptoms, e.g. chronic hepatitis B.


Antiviral Therapy I. Antiviral Drugs (modes of action): Inhibition of uncoating

Inhibition of viral RNA polymerase

Inhibition of viral DNA polymerase

Reverse transcriptase inhibitors

Protease inhibitors

Inhibition of virus release

Interferons (IFNs, type I)



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I. Antiviral Drugs

1- Inhibition of Uncoating

Amantadine/rimantadine: Inhibits uncoating of influenza A virus,therefore used in prevention of its infection.


Antiviral Drugs

2- Inhibit Viral DNA Polymerase1- Acyclovir (Zovirax):

e.g. active against HSV-I, II and Varicella Zoster virus.

- Topical acyclovir.

-Parenteral acyclovir.

- Oral

2- Ganciclovir: similar to acyclovir but more effective againstCytomegalovirus [CMV].

- Ribavirin: It inhibits synthesis of mRNA.



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Antiviral Drugs

4- Inhibit Reverse transcriptase [RT] Zidovudine, AZT: It inhibits viral RT enzyme. It is used in treatment of

AIDS.

Lamivudine (3 TC) and Stavudine (d4T): Both inhibit RT enzyme of HIV


5- Protease Inhibitors Proteases are needed in the late stage of HIV replication.

Indinavir is a model of protease inhibitors.

6- Inhibition of Virus release: Tamiflu oseltamivir



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II. Interferons (IFNs)

These are host coded proteins (cytokines) that inhibit viralreplication.

They are the first line of defense against viral infections.


Diagnostic Methods in Virology

1. Direct Detection

2. Virus Amplification

3. Serology



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Direct Detection

1. Virus particlesVirus particles By Electron Microscopy


2. Detection of Inclusion bodies by Light Microscopy

Normal stains as Giemsa or H&E

Special stains as Sellers stain as in rabies virus



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3. Antigen Detection

immunofluorescence,

immunoperoxidase ,

cell ELISA

Soluble Ag ELISA, AGPT[agar gel

prec p a on es , e c


4. Viral Genome Detection

Purification of nucleic acid and detection by

Dot blot hybridization

Restriction fragment length polymorphism analysis[RFLP]



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Virus AmplificationA In-vivo

1. Cell Culture

2. Embryonated Eggs

3. Animals


Types of Cell Culture

1. Primary cell lines:

2. Human diploid cell culture: Human embryonic lung

3. Continuous cell lines:Prepared fromTumor cells.



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Detection of Virus Replication in Cell Culture

1. Cytopathic effect (CPE):

- Cell death or lysis.- Syncytial formation (giant cells):

Fusion of membranes of adjacent cells to form multinucleated giant cells.

- Inclusion bodies:

These are either the site of virus assembly or degenerative changes in the cell.a- Intracytoplasmic: e.g. rabies.

b- Intranuclear: e.g. herpes viruses.

c- Both: e.g. measles virus.

-Plaque formation:

Plaques are areas of virally-infected cells in a cell culture.


Viral Plaques



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In vitro amplification


Serology

convalescent stages of infection, or the detection of IgM in

primary infection.

Classical Techniques Newer Techniques

1.

Complement fixation tests (CFT) 1.

Radioimmunoassay (RIA)

.

.

3.

Immunofluorescence techniques (IF) 3.

Particle agglutination

4.

Neutralization tests 4.

Western Blot (WB)

5.

Counter-immunoelectrophoresis 5.

RIBA, Line immunoassay



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Serology

4 fold or more increase in titre of IgG or total antibody

between acute and convalescent sera

Presence of IgM

Seroconversion

s ng e g t tre o g or tota ant o y) - very

unreliable


Typical Serological Profile After Acute Infection

Note that during reinfection, IgM may be absent or present at a low level transiently



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Complement Fixation Test

Complement Fixation Test in Microtiter Plate.


ELISA for antibody

Microplate ELISA for HIV antibody: coloured wells indicate reactivity


WEEK 5 Viruses 2nd year - 2013 2014 [وضع التوافق].pdf

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