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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
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
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Virus: Structural components
1.Nucleic acid
2.Protein coat [capsid]
3.Envelope in some viruses only
Nucleocapsid
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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).
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
viruses are not found inside the cell.
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Prof. Ahmed Sayed Abdel-Moneim
Prof. Ahmed Sayed Abdel-Moneim
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Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
.
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
Prof. Ahmed Sayed Abdel-Moneim
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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.
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
Viral Plaques
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In vitro amplification
Prof. Ahmed Sayed Abdel-Moneim
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
Prof. Ahmed Sayed Abdel-Moneim
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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
Prof. Ahmed Sayed Abdel-Moneim
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.
Prof. Ahmed Sayed Abdel-Moneim
ELISA for antibody
Microplate ELISA for HIV antibody: coloured wells indicate reactivity
Prof. Ahmed Sayed Abdel-Moneim