Download Virology

Virology
Introduction
Early period identification
Recent identification
What is virus?
"Virus" is from the Greek
meaning for "poison" and was
initially described by Edward
Jenner in 1798.
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Obligatory intracellular parasite
Smallest infectious agent
Has simple structure
Has one type of nucleic acid
Not true cell
lacks ribosome
mitochondria
cell wall
ribosome
Viral structure
Viral classification
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Old classification
Type of host: human, animal, plant..etc
Tissue affinity: neurotropic, viscerotropic.etc
Geographical location: Coxsackie, Newcastle
 Recent
classification
Nature of N.A: single, double stranded
DNA or RNA
Shape : icosahedra, helical, complex
Envelop: enveloped or non-enveloped
Assembly: cytoplasm, nucleus
Physical and chemical nature: size,
sensitivity, dimension
Viral replication
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Attachment:
Penetration
Uncoating
Replication
Assembly and
realase
Pathogenic effect on host cells
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1.
Permissive cells
Destruction
(lysis)
2. Cell fusion (syncytia)
3. Inclusion bodies
4. Transformation
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4.
Non permissive cells
Latent
Chronic (persistent)
Oncogenic
Slow
Viral cultivation
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1.
2.
3.
Cell culture
Organ culture: slice of organ
Tissue culture: fragment of minced organ
Cell culture:
Primary CT: variety of cells with limited growth
(5-10)
Diploid CT : single type divided up to 100 times
derived from embryo
Continuous CT: single type, indefinite growth,
originated from cancer
Cell culture serves purposes
1.
2.
3.
Primary isolation
Vaccine production
Basic researches
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Embryonated eggs
F Viruses cannot be grown
on sterile media, but require
the presence of specific host
cells.
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Laboratory animals
Route and spread of viral infection
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Vertical (congenital) ……. Rubella
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Viral zoonosis from animal to human, Orf
Horizontal
Skin route
warts
Oral route
entrovirus
Respiratory route
rhinovirus
Urogenital route (sexually transmitted)
CMV
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Viral spread
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Direct
lymphatic
Viraemia
CNS
PNS
Viral Diagnosis
Viral infection
clinical criteria
(By the time virus isolation has been made,
patient is either died or recovered)
Importance of viral diagnosis
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Management of the patient…. Rubella
Management of the patient’s contact.. HBV
Study the effectiveness of immunization HBV, HIV
Epidemiological surveillance
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screening of blood donors
distribution of particular virus
investigation of new outbreak
Viral diagnostic techniques
1.
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Direct
Electron microscope (stool exam for
Rota virus)
Detection of viral antigen in infected
cell by FAT
Viral isolation in TC or lab. animals
2. Indirect
serological tests to identify unknown
virus by known antibodies
ELISA
RIA
FAT
CFT
Interferons
Low m.wt proteins confer cell
ability to resist viral infection
 Host specific
 Non specific antiviral activity
Types
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Alpha IF
Beta IF
Gamma IF
leukocytes
fibroblast
lymphocytes
Mechanism of interferons
Released IF from infected cell
interact with membrane of surrounding
cells resulting in the production of:
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Endonucleases: degrade RNA
Protein kinases: block initiation of protein
synthesis
Viral Vaccines
Traditional
approach
prevention rather than cure
great success WHO program
eradication of small pox
Why we use vaccines?
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Cheaper
Prophylactic
Prevent congenital abnormalities
Control disease and eradicate it
Types of Viral Vaccines
1.
Live attenuated vaccine
attenuation for human
not natural host
treated in cell culture
e.g. polio virus
disadvantage: revertant
shelf life
mutant
2. Killed or inactivated vaccines
safer than live e.g. Rabies
disadvantage:
complete inactivation
shelf life
3. Subunit vaccine
recombinant DNA technology
production of free N.A vaccine
e.g. HBs Ag
Viral chemotherapy
Type of viral infections
lytic
persistent
latent
Antiviral are nucleoside analogues
(precursors of DNA or RNA)
Acyclovir (zovirax)
affect on herpes viruses
(inhibit DNA synthesis)
 Amantadine
treatment of influenza virus
( prevent shedding of virus)
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Ribavirin
treatment of RSV, Lassa fever
(inhibit binding of mRNA to
ribosome)
 AZT
act on reverse transcriptase
of HIV
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Viriods
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Smallest agents
Cause plant disease
Naked, closed circular ss RNA
Replicate using host cell enzymes
Not associated with human disease
Prions
(proteinaceous infectious particles)
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Cause disease of long i.p.
Neither viruses nor viriods
Do not have either DNA or RNA
Ability to self replicate
Cause scrapie (CNS dis. of sheep)
Resistant to heat & chemicals
Transmitted to animals by ingestion
Neurological transmission has been
reported
Prions induced diseases
Kuru
fatal neurological disease
 Creutzfeldt-jakob
chronic encephalopathy
** prions replicate first in lymph
tissue
brain
intracellular
vacuoles
spongy like appearance
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Prevention & dental implication
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No treatment or vaccines
Not consuming susceptible food
Disposable equipments in dental
practice should be incinerated
Autoclave instruments at 131 for
18 min.