Virology for medical laboratory introduction to virus(2).ppt

Virology for medical laboratory

1. Medical Virology

2. Definition of Virus
Viruses may be defined as acellular
organisms whose genomes consist of nucleic
acid, and which obligately replicate inside
host cells using host metabolic machinery
and ribosomes to form a pool of components
which assemble into particles called virions,
which serve to protect the genome and to
transfer it to other cells

3. Viral Properties
Viruses are inert (nucleoprotein ) filterable
Agents
Viruses are obligate intracellular parasites
Viruses cannot make energy or proteins
independent of a host cell
Viral genome are RNA or DNA but not both.
Viruses have a naked capsid or envelope
with attached proteins
Viruses do not have the genetic capability to
multiply by division.
Viruses are non-living entities

4. Consequences of Viral Properties
Viruses must be infectious to endure in
nature
Viruses must be able to use host cell
processes to produce their components
(viral messenger RNA, protein, and
identical copies of the genome)
Viruses must encode any required
processes not provided by the cell
Viral components must self-assemble

5. Size of Viruses
A small virus has a diameter of about
20nm.
-Parvovirus
A large virus have a diameter of up to
400nm.
-Poxviruses

7. Shape of Viruses
Spherical
Rod-shaped
Brick-shaped
Tadpole-shaped
Bullet-shaped
Filament

8. Shapes of Viruses:Spherical

9. Structure of Viruses
Virion
The complete infectious unit of virus particle is
Structurally mature, extracellular virus particles.
Viral core
The viral nucleic acid genome,In the center of
the virion, :Control the viral heredity and
variation, responsible for the infectivity

10. Virion
Capsid
Viral core
envelope

11. CHEMICAL COMPOSITION OF
VIRUSES
Viral Protein
Viral Nucleic Acid
Viral Lipids
Viral carbohydrate

14. Genome
The genome of a virus can be either DNA or
RNA
DNA-double stranded (ds): linear or circular
Single stranded (ss) : linear or circular
RNA-ss:segmentedor non-segmented
ss:polarity+(sense) or polarity –(non-
sense)
ds: linear (only reovirusfamily)

15. DNA RNA
double-
stranded
single-
stranded
double-
stranded
single-stranded
lin
ear
circular
lin
ear
circularlinear linear (circular)*
sin
gle
sin
gle
mult
iple
sin
gle
sin
gle
mult
iple
sin
gle
multi
ple
(+)sense(-)sense
sin
gle
mult
iple
sin
gle
mult
iple

16. The Structure & Complexity of Virus
Genomes
The nucleic acid comprising the genome may be
single-stranded or double-stranded, & in a linear,
circular or segmented configuration. Single-
stranded virus genomes may be:
positive (+)sense, i.e. of the same polarity
(nucleotide sequence) as mRNA
negative (-)sense
ambisense -a mixture of the two.

17. Viral Nucleic Acid
DNA-double stranded (ds): linear or circular
Single stranded (ss) : linear or circular
RNA-ss:segmented or non-segmented
ss:polarity+(sense) or polarity –(non-
sense)
ds: linear (only reovirus family)
Viral Protein
Structural protein (Capsomere)
Enzyme
glycoproteins (spike/viral attachment
protein, VAP)

18. Genome
The genome of a virus can be either DNA
or RNA
DNA-double stranded (ds): linear or circular
Single stranded (ss) : linear or circular
RNA-ss:segmented or non-segmented
ss:polarity+(sense) or polarity –(non-sense)
ds: linear (only reovirus family)

23. Survey of RNA-containing
Viruses
Picornaviruses
Astroviruses
Caliciviruses
Reoviruses
Arboviruses
Togaviruses
Flaviviruses
Arenaviruses
Coronaviruses: SARS
Retroviruses
Bunyaviruses
Othomyxoviruses
Paramyxoviruses:
Rhabdoviruses:rabies
virus
Bornaviruses: BDV
Filoviruses
Other viruses
Viroids

26. Viral Capsid
The protein shell, or coat, that encloses the
nucleic acid genome.
Protect the viral nucleic acid.
Participate in the viral infection and Share
the antigenicity
Nucleocapsid
The core of a virus particle consisting of
the genome plus a complex of proteins.
complex of proteins = Structural proteins
+Non-Structural proteins (Enzymes
&Nucleic acid binding proteins)

27. Baltimore classification groups viruses
together based on their manner of mRNA
synthesis. Characteristics directly related to
this include whether the genome is made
ofdeoxyribonucleic acid(DNA)
orribonucleic acid(RNA), the strandedness
of the genome, which can be either single-
or double-stranded, and the sense of a
single-stranded genome, which is either
positive or negative.

28. Baltimore classification distinct groups.
Group I: double-stranded DNA viruses
Group II: single-stranded DNA viruses
Group III: double-stranded RNA viruses
Group IV: positive sense single-stranded RNA
viruses
Group V: negative sense single-stranded RNA
viruses
Group VI: single-stranded RNA viruses with a
DNA intermediate in their life cycle
Group VII: double-stranded DNA viruses with an
RNA intermediate in their life cycle

29. Virus FamilyEnvelope
Present
Capsid
Symmetry
DNA Structure
1
Medically
Important
Viruses
Parvovirus No IcosahedralSS, linear B19 virus
PolyomavirusNo IcosahedralDS, circular, supercoiledJC virus, BK
virus
PapillomavirusNo IcosahedralDS, circular, supercoiledHuman
papilloma virus
Adenovirus No IcosahedralDS, linear Adenovirus
HepadnavirusYes IcosahedralDS, incomplete circularHepatitis B virus
Herpesvirus Yes IcosahedralDS, linear Herpes simplex
virus, varicella-
zoster virus,
cytomegalovirus
, Epstein-Barr
virus
Poxvirus Yes Complex DS, linear Smallpox virus,
molluscum
contagiosum
virus

30. Virus Family Envelop
e
Capsid
Symmetry
RNA Structure Medically Important Viruses
Picornavirus No IcosahedralSS linear,
nonsegmented,
positive polarity
Poliovirus, rhinovirus, hepatitis A virus
Hepevirus No IcosahedralSS, linear, non-
segmented, positive
polarity
Hepatitis E virus
Calicivirus No IcosahedralSS linear,
nonsegmented,
positive polarity
Norwalk virus
Reovirus No IcosahedralDS linear, 10 or 11
segments
Rotavirus
Flavivirus Yes IcosahedralSS linear,
nonsegmented,
positive polarity
Yellow fever virus, dengue virus, West Nile virus,
hepatitis C virus
Togavirus Yes IcosahedralSS linear,
nonsegmented,
positive polarity
Rubella virus
Retrovirus Yes IcosahedralSS linear, 2 identical
strands (diploid),
positive polarity
HIV, human T-cell leukemia virus
Orthomyxovirus Yes Helical SS linear, 8
segments, negative
polarity
Influenza virus
Paramyxovirus Yes Helical SS linear,
nonsegmented,
negative polarity
Measles virus, mumps virus, respiratory syncytial
virus

31. Virus FamilyEnvelope
Present
Capsid
Symmetry
RNA StructureMedically Important
Viruses
RhabdovirusYes Helical SS linear,
nonsegmented,
negative polarity
Rabies virus
Filovirus Yes Helical SS linear,
nonsegmented,
negative polarity
Ebola virus, Marburg
virus
CoronavirusYes Helical SS linear,
nonsegmented,
positive polarity
Coronavirus
Arenavirus Yes Helical SS circular, 2
segments with
cohesive ends,
negative polarity
Lymphocytic
choriomeningitis virus
Bunyavirus Yes Helical SS circular, 3
segments with
cohesive ends,
negative polarity
California encephalitis
virus, hantavirus
Deltavirus Yes Uncertain
4
SS circular,
closed circle,
negative polarity
Hepatitis delta virus

32. Symmetry of Nucleocapsid
Helical
California Encephalitis Virus
Coronavirus
Hantavirus
Influenza Virus (Flu Virus)
Measles Virus ( Rubeola)
Mumps Virus
Parainfluenza Virus
Rabies Virus
Respiratory Syncytial Virus(RSV)

33. Cubic or icosahedral symmetry

34. Icosahedral
Adeno-associated Virus
(AAV)
Adenovirus
B19
Coxsackievirus-A
Coxsackievirus-B
Cytomegalovirus (CMV)
Eastern Equine
Encephalitis Virus
(EEEV)
Echovirus
Epstein-Barr Virus
(EBV)
Hepatitis A Virus (HAV)
Hepatitis B Virus (HBV)
Hepatitis C Virus (HCV)
Hepatitis Delta Virus
(HDV)
Hepatitis E Virus (HEV)
Herpes Simplex Virus 1
(HHV1)
Herpes Simplex Virus 2
(HHV2)
HIV
Human T-lymphotrophic
Virus (HTLV)
Norwalk Virus
Papilloma Virus (HPV)
Polio virus
Rhinovirus
Rubella Virus
Saint Louis Encephalitis
Virus
Varicella-Zoster Virus
(HHV3)
Western Equine
Encephalitis Virus (WEEV)

35. Complex Virus Structures
A well known example is the tailed
bacteriophagessuch as T4.
The head of these viruses is cubic with a
triangulation number of 7. This is attached
by a collar to a contractile tail with helical
symmetry.

36. Properties of naked viruses
Stable in hostile environment
Not damaged by drying, acid, detergent, and
heat
Released by lysisof host cells
Can sustain in dry environment
Can infect the GI tract and survive the acid and
bile
Can spread easily via hands, dust, fomites, etc
Can stay dry and still retain infectivity
Neutralizing mucosal and systemic antibodies
are needed to control the establishment of

37. Naked viruses( Non Enveloped )
Adeno-associated Virus (AAV)
Adenovirus
B19
Coxsackievirus -A
Coxsackievirus -B
Echovirus
Hepatitis A Virus (HAV)
Hepatitis E Virus (HEV)
Norwalk Virus

38. Envelope
A lipid-containing membrane that surrounds
some viral particles.
It is acquired during viral maturation by a
budding process through a cellular
membrane, Viruses-encoded glycoproteins
are exposed on the surface of the envelope.
Function-Antigenicity
some viruses possess neuraminidase
Infectivity
Resistance

39. Envelope

40. Properties of enveloped viruses
Labile in dry , arid environment
Damaged by drying, acid, detergent, and
heat
Pick up new cell membrane during
multiplication
transmitted in the protective, droplets,
secretions, blood and body fluids
Insert new virus-specific proteins after
assembly
Must not infect the GI tract for survival
Virus is released by budding

41. Enveloped
California Encephalitis Virus
Coronavirus
Cytomegalovirus (CMV)
Eastern Equine Encephalitis
Virus (EEEV)
Epstein-Barr Virus (EBV)
Hantavirus
Hepatitis B Virus (HBV)
Hepatitis C Virus (HCV)
Hepatitis Delta Virus (HDV)
Herpes Simplex Virus 1 (HHV1)
Rotavirus
Rubella Virus
Saint Louis Encephalitis Virus
Smallpox Virus (Variola)
Vaccinia Virus
Herpes Simplex Virus 2 (HHV2)
Human Immunodeficiency
Virus (HIV)
Human T-lymphotrophic Virus
(HTLV)
Influenza Virus (Flu Virus)
Molluscum contagiosum
Papilloma Virus (HPV)
Polio virus
Rhinovirus
Varicella-Zoster Virus (HHV3)
Venezuelan Equine Encephal.
Vir. (VEEV)
Western Equine Encephalitis
Virus (WEEV)
Yellow Fever Virus

42. Enveloped
Virus
Naked
Virus
Cubic Helical

43. Replication of Viruses

44. Replicativecycle
As obligate intracellular parasites, Virus
must enter and replicate in living cells in
order to “reproduce”themselves. This
“growth cycle”involves specific attachment
of virus, penetration and uncoating, nucleic
acid transcription, protein synthesis,
matureation and assembly of the virions
and their subsequent release from the cell
by budding or lysis

45. 1. Attachment/Adsorption
Virus attaches to the cell surface and Viral
attachment protein recognizes specific
receptors on the cell surface
2. Penetration
Virions are either engulfed into vacuoles by
“endocytosis” or the virus envelope fuses
with the plasma membrane to facilitate
entry
2 systems
Fusion -by fusing with the plasma
membrane
Endocytosis-Entry via endosomes at the
cell surface

46. 3. Uncoating
Nucleic acid has to be sufficiently uncoated
that virus replication can begin at this stage
Uncoating is usually achieved by cellular
proteases “opening up” the capsid
4.Biosynthesisi.e.genome synthesis, mRNA
production and protein synthesis
5.Maturation-The stage of viral replication at
which a virus particle becomes infectious;
nucleic acids and capsids are assembled
together.

47. 6. Assembly-The stage of replication during
which all the structural components come
together at one site in the cell and the basic
structure of the virus particle is formed.
Release-Disintegration : naked virus cause
the host cell lysis
Budding: enveloped virusesdo not
necessarily kill the cell