General characteristics of Viruses

General characteristics of Viruses
Introduction
I. Conception

1. Virus: Viruses are obligate intracellular parasites at the genetic level.

2. Virion: The entire infectious unit or the complete virus particles

3. Atypical virus like agents (subvirus)
1)   Viroid: Viroids consist solely of a single molecule of circular RNA without a protein coat or envelope.
 

I.
Introduction
I. Conception
2)  Prion (unconventional virus) Prion are infectious protein particle that are composed solely of protein, i.e. they contain no detectable nucleic acid.
CJD
Kuru
Fatal Familial Insomnia
Scrapie of sheep and goat
Bovine spongiform Encephalopathy (BSE)
3)   Satellites: virusoid
Satellites
Introduction
II. Developing history

III. Medical Virology
Basic properties of viruses

. Structure and Chemical composition of viruses

1.   Size and shape
Measuring the size of viruses.

A . Direct observation in the electron microscope
B . Filtration through membranes of graded
C . Sedimentation in the ultracentrifuge
D . Comparative measurements
1. Size and shape
Basic properties of viruses
2.   Basic structure
1)   Nonenveloped virion

Nonenveloped virion
Basic properties of viruses
2)   Enveloped virion

Enveloped virion
Basic properties of viruses
3)   Types of symmetry
A . Cubic symmetry
B . Helical symmetry
C . Complex structure
Types of symmetry
Basic properties of viruses
3.   Chemical composition
1)   Nucleic acid
DNA: dsDNA; ssDNA
RNA:+ssRNA; -ssRNA; dsRNA; +ssRNA Retroviridae

Nucleic acid 3-1
Nucleic acid 3-2
Nucleic acid 3-3
Basic properties of viruses
2)   proteins
3)   lipids
4)   carbohydrates
Basic properties of viruses
II.   Viral Replication
1. Replication
2. Steps in Viral replication
1)   Recognition and attachment to the target cell
2)   Penetration
3)   Uncoating
4)   Gene expression & genome replication
5)   Assembly & release

Steps in Viral replication
Replication: example 1
Replication: example 2
Replication: example 3
Basic properties of viruses
Abnormal multiplication
A.   Defective virus: A virus particle that is functionally deficient in some aspect of replication.
B.   Abortive infection: Infection in which some or all virus components are synthezised but no infective virus is produced.
Viral pathogenicity and Immunity
In this section, you will learn:
$ Viral Pathogenicity
$ Immunity for viral infection
Viral pathogenicity and Immunity

I. Viral Pathogenicity

Viral Pathogenicity
Viral pathogenicity and Immunity
1.   modes of transmissions
1)   Horizontal transmission: Transmission
between person of any age after birth, usually
excluding via the maternal milk.

  modes of transmissions
1)   Horizontal transmission 2-1
  modes of transmissions
1)   Horizontal
transmission
Viral pathogenicity and Immunity
2)   Vertical transmission: Spread of infection parent to the young via the placenta or genital tract.
Transmission via the maternal milk is sometime included.

Vertical transmission
Viral pathogenicity and Immunity
2.   Types of viral infections
1)   inapparent infections
2)   apparent infections
A.   Acute infection
B.   Persistent infection
a) chronical infection: HBV
b)  latent infection: HSV
Varicella--zoster virus

latent infection: HSV
Viral pathogenicity and Immunity
C) slow virus infection （HIV. kuru)
D) delayed complication after acute viral infection.
SSPE
Viral pathogenicity and Immunity
3.Viruses-host interaction
1)   cell level
A.   lytic infection (Cytocidal infection) : cytopathic effect ( CPE ) Alternation in the Microscopic apperance of cell in culture following infection with a virus.
B.   steady state infection : fusion of cells, new antigen.
C.   integration
D.   apoptosis
E.    inclusion body: An area of abnormal staining in a virus- infected cell.
F.    Cell transformation : alternation in cell morphology and / or behaviour, …….


Viral pathogenicity and Immunity
3.Viruses-host interaction
2)   Host immune response
A.   inflammatory reaction
Bacteria : inflitration of polymophonuclear leukocyte
Viruses : inflitration of mononuclear cell and lymphocytes.
B. Immune pathology
a. Cell-mediated immunity : measles virus , HIV
b. Antibody-mediated immunity : dengue virus : ab+RBC+C----hemolysis, HBV

Viral pathogenicity and Immunity
II.   Immunity for viral infection
1.   non-specific immune NK , IFN
1)   Interference phenomenon
A.   Definition : prevention of the replication of one virus by another.
B.   Types of interference
C.   Mechanisms of interference

Viral pathogenicity and Immunity
2)   Interferon (IFN)
A.   Definition: Interferons(IFNs) are host-coded proteins of the large cytokine family that inhibit viral replication; they are produced by intact animals or cultured cells in response to viral infection or other inducers.
B.   types of IFN
C.   antiviral activity
Antiviral activity
Viral pathogenicity and Immunity
2.   Specific immune
1)   humoral immune
A.   Neutralization antibodies
B.   Hemagglutination antibodies
C.   CF antibodies
2)   Cellular immunity
Laboratory Diagnosis of Viral Disease
In this section, you will learn:
$ Introduction
$ Procedure
Laboratory Diagnosis of Viral Disease
Introduction
Object

Procedure
I.   Specimens
1.   Kinds of specimen
2.   Time
Laboratory Diagnosis of Viral Disease
II.   Methods
1.   Cytology
2.   Electron microscopy
3.   Viral isolation
1)   animals
2)   chicken embryo
3)   Tissue culture
A.   Definition: The growth or maintenance of living tissue in a liquid or soft gel medium in vitro.

Laboratory Diagnosis of Viral Disease
B.   Types of cell culture
a. Primary cell culture
b. Cell line
C.   Detection of virus-infected cells
a. CPE
b. Adsorption of RBC
c. Interference
d. PCR
Detection of virus-infected cells: CPE
Detection of virus-infected cells: CPE
Laboratory Diagnosis of Viral Disease
D.   Quantitation of viruses
a. TCID50(50% Tissue culture infected dose ): Infections dose of 50% CPE of tissue cultures caused by viral minimum infected dose is called TCID50
b. PFU : under controlled condition,single plague can arise from a single infection virus particle, termed a plague-forming unit.

Laboratory Diagnosis of Viral Disease
4.   Serologic methods
1)   complement fixation
2)   Hemagglutination inhibition
3)   Neutralization
4)   Fluorescent antibody
5)   Radioimmunoassay
6)   Enzyme-linked Immunosorbent Assay (ELISA)

Laboratory Diagnosis of Viral Disease
5.   Detection of viral genetic material
1)   nucleic acid hybridization technique :
a. Southern blot
b. Northern blot
2)   polymerase chain reaction (PCR), RT-PCR
6.   Western blot
7.   Biochip/DNA microarray/gene chip
Antiviral Therapy and Immune prophylaxis
In this section, you will learn:
$ The treatment with and prevention from viral diseases
Antiviral Therapy and Immune prophylaxis

I. Antiviral Agent

II. Immunoglobulins

III. Immunomodulators

Immunomodulators
Antiviral Therapy and Immune prophylaxis
IV. Gene therapy
a. Antisense oligonucleotide, ASON
b. Short interfering RNA, siRNA
C. Ribozyme
V. Vaccine
1. Inactivated vaccine
2. Attenuated vaccine
3. Genetic engineering vaccine
4. DNA Vaccine