virology

Virology 3rd Year lecture1 College of Dentistry

Text book: Essenial Microbiology for Dentistry by Samaranayake
Introduction
Early period of identification
Recent identification
What is virus?

Virus" is from the Greek meaning for "poison" and was initially described by Edward Jenner in 1798.

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


 SHAPE \* MERGEFORMAT 


Viral classification

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

Attachment:
Penetration
Uncoating
Replication
Assembly and Realase
 SHAPE \* MERGEFORMAT 



Pathogenic effect on host cells
Permissive cells
Destruction (lysis)
Cell fusion (syncytia)
Inclusion bodies
Transformation
Non permissive cells
Latent
Chronic (persistent)
Oncogenic
Slow

Viral cultivation

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
Primary isolation
Vaccine production
Basic researches

Embryonated eggs

Laboratory animals

Route and spread of viral infection

Vertical (congenital) . Rubella
Viral zoonosis from animal to human, Orf
Horizontal
Skin route , warts
Oral route entrovirus
Respiratory route rhinovirus
Urogenital route (sexually transmitted) CMV

Viral spread: direct, lymphatic, viraemia, CNS, PNS

Viral Diagnosis


Viral infection diagnosed by clinical criteria??
(By the time virus isolation has been made, patient is either died or recovered)
Importance of viral diagnosis

Management of the patient. Rubella

Management of the patients contact.. HBV
Study the effectiveness of immunization HBV, HIV
Epidemiological surveillance
* screening of blood donors
* distribution of particular virus
* investigation of new outbreak

Viral diagnostic techniques

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, etc


Interferons

Low m.wt proteins confer cell ability to resist viral infection

Host specific
Non specific antiviral activity

Types

Alpha IF leukocytes
Beta IF fibroblast
Gamma IF lymphocytes

Mechanism of interferons

Released IF from infected cell

interact with membrane of surrounding cells resulting in the production of:

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?
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 mutant
e.g. polio virus ;
disadvantage: revertant
shelf life
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)
Ribavirin : treatment of RSV, Lassa fever (inhibit binding of mRNA to ribosome)
AZT
act on reverse transcriptase of HIV

Viriods

Smallest agents
Cause plant disease
Naked, closed circular ss RNA
Replicate using host cell enzymes
Not associated with human disease


Prions(proteinaceous infectious particles)
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

Prevention & dental implication

No treatment or vaccines
Not consuming susceptible food
Disposable equipments in dental practice should be incinerated
Autoclave instruments at 131 for 18 min.










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