DR MONIKA RAJANI ASSOCIATE PROFESSOR DEPT OF MICROBIOLOGY CIMSH LKO Dr Monika Rajani Dr Monika Rajani VIRUSES Neither prokaryotes nor eukaryotes No cellular organisation Contain either DNA or RNA ID: 932484
Download Presentation The PPT/PDF document "GENERAL PROPERTIES OF VIRUSES" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
GENERAL PROPERTIES OF VIRUSES
DR MONIKA RAJANI
ASSOCIATE PROFESSOR ,DEPT OF MICROBIOLOGYCIMSH ,LKO
Dr Monika Rajani
Slide2Dr Monika Rajani
Slide3VIRUSES
Neither prokaryotes nor eukaryotesNo cellular organisation.
Contain either DNA or RNA but neither both.Obligate intracellular parasitesLack enzymes necessary for protein and nucleic acid synthesis
Multiply by complex process
Unaffected by antibiotics.
Can cause common cold to
deadly AIDS
Twilight zone
that separates living from non living .
Dr Monika Rajani
Slide4CHEMICALS
Can be
crystallised
as chemicals
Can be
crystallisedccc
as
chemicalsc
Dr Monika Rajani
Slide5Dr Monika Rajani
Slide6MORPHOLOGY
Smaller than bacteria(1um:0.01um)Viruses=20-300 nm: bacteria 1000 nm
FilterableCan be only seen under electron microscope except pox virusesSmallest virus: parvovirus (20 nm)
Largest virus
: pox virus (300 nm)
Dr Monika Rajani
Slide7Dr Monika Rajani
Slide8Dr Monika Rajani
Slide9ENVELOPE
Enveloped or non enveloped(naked)Envelope derived from host cell membrane
LipoproteinLipid=host;protein=virusPeplomeres
: protein spikes projecting from envelope
Enveloped viruses are susceptible to lipid solvents.
Antigenic
Attatchment
to host cell surface.Hemagglutination
Dr Monika Rajani
Slide10CAPSID
Protein coat-polypeptide
Nucleocapsid: capsid with enclosed NAUnits: capsomeres
The chemical units of
capsids
are polypeptide molecules
arranged symmetrically
to form an impenetrable shell around NA coreFn:to introduce viral genome into host cell
Protects the NA from inactivation by nucleases
Dr Monika Rajani
Slide11Symmetry
Icosahedral(cubical)- polygon -1-herpes virus
Helical- spiral tube-TMVComplex- pox viruses
Dr Monika Rajani
Slide12Symmetry of
capsid Icosahedral Helical Complex
-polygon with 12 -capsomeres & NA - pox viruses
vertices and 20 sides wounded together
-
pentons
at vertices to form helical tube
and
hexons
at facets
Dr Monika Rajani
Slide13StructureCHEMICAL NATURE
Nucleic acid: either DNA or RNA
Unique as nowhere else in nature nucleic information is carried solely by RNA.ProteinsLipidsOthers:carbohydrate :enzymes
Dr Monika Rajani
Slide14Definitions
Virion:
Intact viral particleViroid: protein free subviral agent with small genome in form of low molecular weight RNA :first identified in
potato spindle tuber disease
Prions
:
proteinaceous
infectious particles without NA
Dr Monika Rajani
Slide15CLASSIFICATION OF VIRUSES
DNA VIRUS
ss DNA: :Parvoviridae
ds
DNA
:Pox
viridae
:
Adenoviridae
:
Herpesviridae
:
Papovaviridae
:
Hepadnaviridae
RNA VIRUS
ss
RNA:
Picornaviridae
Orthomyxo
viridae
Paramyxoviridae
Flaviviridae
Rhabdoviridae
Bunya
viridae
Arena
viridae
Corona
viridae
Retroviridae
Calciviridae
ds
RNA
:
Reoviridae
Dr Monika Rajani
Slide16Shape
Spherical: Herpes virus
Bullet shaped : Rabies virusFilamentous : Ebola virusBrick s
haped : Pox virus
Rod
shaped: TMV
Dr Monika Rajani
Slide17RESISTANCE
Heat labileStable at low temperatures= -70
C,lyophilisation,freeze driedDisrupted under alkaline conditions.Inactivated by sunlight and uv raysInactivated by H
2
O
2
,pottasium
permanganate,and
hypochorites
Organic iodine compounds are actively
virucidal
.
Formaldehyde and BPL are actively
virucidal
Hepatitis viruses and polioviruses
are resistant to chlorination.Dr Monika Rajani
Slide18VIRAL HEMAGGLUTINATION
Originally observed in influenza viruses.
Property of agglutination of RBCs from different sppDue to :
:
Hemagglutinin
spikes
on surface
:Neuraminidase-RDEDestruction of receptor leads to reversal of hemagglutination
and release of virus from cell surface-
ELUTION
Dr Monika Rajani
Slide19VIRAL HEMAGGLUTINATION
Application: detection and assay
of influenza viruses :Purification and concentration of viruses :Detection of
antiviral AB
by HAI test
HA also observed in measles
virus,rubella,enterovirus,rabies,reovirus,parainfluenza
virus
Dr Monika Rajani
Slide20Viral assay
To detect
virus content in a specimenBy measuring total virus particles or only infectious
virions
.
By counting under electron microscope
Hemagglutination
titre
: virus count
Types of assays of infectivity:
Quantitative
:
measure actual number of infectious
particles.Eg- plaque assay and pock assay
Quantal: indicates only presence or absence of infectious viruses by death or CPEDr Monika Rajani
Slide21Viral multiplication
Virus lacks biosynthetic enzymes
for replicationDepend upon synthetic machinery of host cell for replication.Steps:1-Adsorption- receptors on virus surface
:2-
Penetration
-either whole virus or NA alone
:3-
Uncoating
- release of NA in host cell
:4-
Biosynthesis of NA
and
capsid
protein
-transcription of m RNA -
Translation
of early
proteins:ENZYMES
-
replication
of NA
-
synthesis of late
proteins
:components
of daughter
virions
Dr Monika Rajani
Slide22Viral multiplication
5-Maturation-assembly of daughter virions
6-Release of daughter virions- lysis or budding
Eclipse phase:
:
from the stage of penetration till appearance of daughter
virions
the
virus cannot be demonstrated in host cell.During
this period virus remains underground
Defective
viruses
:
genetically
deficient viruses require activity of helper viruses to produce daughter virions.eg:HDV
Dr Monika Rajani
Slide23STEPS OF VIRAL MULTIPLICATION
Dr Monika Rajani
Slide24CULTIVATION OF VIRUSES
Viruses are obligate intracellular parasites and cannot be grown on inanimate culture medium.Methods:
:Animal inoculation :Embryonated eggs :Tissue culture
Dr Monika Rajani
Slide25Animal inoculation
White miceInfant suckling mice- Coxsachie
and Arboviruses.growth indicated by death, disease or visible lesions Drawbacks: -immunity may interfere with viral growth
-Animals
harbour
latent viruses
Dr Monika Rajani
Slide26Embryonated eggs
embryonated hens eggs usedSites of cultivation:
1-Chorioallantoic membrane-CAM- Variola and Vaccinia2-Allantoic cavity-Influenza and Paramyxoviruses
-cultivation of viruses for
vaccine
production
-
eg:yellow
fever(17 D strain) and rabies vaccine(
Flury
strain
)
3-Amniotic sac
-
Infuenza virus4-Yolk sac
- (viruses,chlamydiae and rickettsiae)Dr Monika
Rajani
Slide27TISSUE CULTURE
A:Organ culture
: :bits of organs Eg:tracheal ring culture for isolation of corona viruses
B:
Explant
culture
:
:minced tissue grown embedded in plasma clots
C: Cell culture:tissues are broken into component cells by
proteolytic
enzymes and mechanical shaking
:cells suspended in growth medium
Dr Monika Rajani
Slide28CELL CULTURE
Growth medium- AA,vitamins,salts,glucose,buffers,5% CO2,5% fetal calf serum -antibiotics
-phenol redCell suspension dispenced in bottles and tubes and cells adhere to glass surface
On incubation cells divide to form
a monolayer sheet of cells
in a week
Types of cell culture
:
:Primary cell culture :Diploid cell culture :Continuous cell lines
Dr Monika Rajani
Slide29PRIMARY CELL CULTURE
normal cells freshly taken from body and culturedlimited growth
cannot be maintained in serial cultureEg-rhesus monkey kidney :human embryonic kidney :chick embryo fibroblasts
Dr Monika Rajani
Slide30Diploid cell lines
After first subculture primary cell culture becomes diploid cell culture retain original diploid chromosome
number during serial subcultivation for a limited number of timesEg: WI 38-human embryonic lung strain
:human
diplod
fibroblasts
Dr Monika Rajani
Slide31CONTINUOUS CELL LINES
Derived from cancer cellsCapable of continuous serial cultivation
indefinetlyEG:HeLa:human Ca Cx
HEP 2
:human
epithelioma
larynx
KB
:Ca nasopharynxMc
Coy
:human
synovial carcinoma
Vero
:vervet
monkey kidney cell lineDr Monika Rajani
Slide32Detection of virus growth in cell cultures
1-Cytopathic effect:morphological changes in cultured cells in which viruses grow
Crenation of cells:enterovirusesSyncitium formation:measles
Focal
degeneration
:herpes
viruses
Dr Monika Rajani
Slide33Detection of virus growth in cell cultures
2-Metabolic inhibition:inhibition of cell metabolism due to virus growth no acid production
change in colour of indicator3-hemadsorption:addition of RBCs to cultureRBCs adsorb to surface of cells in case of hemagglutinating
viruses
Dr Monika Rajani
Slide34Detection of virus growth in cell cultures
4- Viral interference:to
test growth of a non cytopathogenic virus by challenge with a second cytopathogenic virus5-Transformation: :
oncogenic
viruses induce cell transformation and loss of contact inhibition.
6-Immunofluorescence:
by staining with
fluoroscent
conjugated antisera
Dr Monika Rajani
Slide35VIRAL GENETICS
Mechanisms of genetic modifications:Mutations:occur during every viral infection
Recombination-occurs when two different but related viruses simultaneously infect a cell and they exchange segments of NA resulting in hybrid
Dr Monika Rajani
Slide36MUTATIONS
mostly lethalTypes of mutants:
:conditional lethal mutant -mutants grow in permissible conditions but are lethal in non permissible
conditions
:temperature sensitive mutant
-permissive and restrictive temperature
:host dependant mutant
-permissive cells
Dr Monika Rajani
Slide37THANK YOU
Dr Monika Rajani