Virology 3Virology 3rdrd Year lecture1 Year lecture1 College of DentistryCollege of Dentistry

Text book: Essenial Microbiology for Dentistry by Text book: Essenial Microbiology for Dentistry by SamaranayakeSamaranayake

IntroductionIntroductionEarly period of identificationEarly period of identificationRecent identificationRecent identificationWhat is virus?What is virus?

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

Obligatory intracellular parasiteObligatory intracellular parasite Smallest infectious agentSmallest infectious agent Has simple structureHas simple structure Has one type of nucleic acidHas one type of nucleic acid Not true cellNot true cell * lacks ribosome* lacks ribosome * mitochondria* mitochondria * cell wall* cell wall * ribosome* ribosomeViral structureViral structure

Viral classificationViral classification Old classificationOld classification

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Type of host: human, animal, plant..etcType of host: human, animal, plant..etc Tissue affinity: neurotropic, viscerotropic.etcTissue affinity: neurotropic, viscerotropic.etc Geographical location: Coxsackie, Newcastle Geographical location: Coxsackie, Newcastle

Recent classification Recent classification Nature of N.A: Nature of N.A: single, double stranded DNA or RNAsingle, double stranded DNA or RNA Shape : Shape : icosahedra, helical, complexicosahedra, helical, complex Envelop: Envelop: enveloped or non-envelopedenveloped or non-enveloped Assembly: Assembly: cytoplasm, nucleuscytoplasm, nucleus Physical and chemical nature:Physical and chemical nature: size, sensitivity, dimension size, sensitivity, dimension

Viral replicationViral replication Attachment: Attachment: PenetrationPenetration UncoatingUncoating ReplicationReplication Assembly andAssembly and RealaseRealase

Pathogenic effect on host cellsPathogenic effect on host cells Permissive cellsPermissive cells

1.1. Destruction (lysis) Destruction (lysis) 2.2. Cell fusion (syncytia)Cell fusion (syncytia)3.3. Inclusion bodiesInclusion bodies

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4.4. TransformationTransformation Non permissive cellsNon permissive cells

1.1. LatentLatent2.2. Chronic (persistent)Chronic (persistent)3.3. OncogenicOncogenic4.4. SlowSlow

Viral cultivationViral cultivation Cell cultureCell culture1.1. Organ culture: slice of organOrgan culture: slice of organ2.2. Tissue culture: fragment of minced organTissue culture: fragment of minced organ3.3. Cell culture: Cell culture:

Primary CT: variety of cells with limited growth(5-10)Primary CT: variety of cells with limited growth(5-10) Diploid CT : single type divided up to 100 times derived from Diploid CT : single type divided up to 100 times derived from

embryoembryo Continuous CT: single type, indefinite growth, originated Continuous CT: single type, indefinite growth, originated from from cancercancer

Cell culture serves purposesCell culture serves purposes1.1. Primary isolationPrimary isolation2.2. Vaccine productionVaccine production3.3. Basic researchesBasic researches

Embryonated eggsEmbryonated eggs Laboratory animalsLaboratory animals

Route and spread of viral infectionRoute and spread of viral infection Vertical (congenital) ……. RubellaVertical (congenital) ……. Rubella Viral zoonosis from animal to human, OrfViral zoonosis from animal to human, Orf HorizontalHorizontal1.1. Skin route , Skin route , wartswarts2.2. Oral routeOral route entrovirusentrovirus3.3. Respiratory routeRespiratory route rhinovirusrhinovirus4.4. Urogenital route (sexually transmitted) CMVUrogenital route (sexually transmitted) CMV

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

Viral DiagnosisViral Diagnosis

Viral infection diagnosed by clinical criteria??Viral infection diagnosed by clinical criteria??

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(By the time virus isolation has been made, patient is either died or (By the time virus isolation has been made, patient is either died or recovered)recovered)

Importance of viral diagnosisImportance of viral diagnosis

Management of the patient…. RubellaManagement of the patient…. Rubella Management of the patient’s contact.. HBVManagement of the patient’s contact.. HBV Study the effectiveness of immunization HBV, HIVStudy the effectiveness of immunization HBV, HIV Epidemiological surveillanceEpidemiological surveillance * screening of blood donors* screening of blood donors * distribution of particular virus* distribution of particular virus * investigation of new outbreak* investigation of new outbreak

Viral diagnostic techniquesViral diagnostic techniques1.1. DirectDirect

Electron microscope (stool exam for Rota virus)Electron microscope (stool exam for Rota virus) Detection of viral antigen in infected cell by FATDetection of viral antigen in infected cell by FAT Viral isolation in TC or lab. animalsViral isolation in TC or lab. animals

2. Indirect2. Indirect serological tests to identify unknown virus by known antibodies serological tests to identify unknown virus by known antibodies

(ELISA, RIA, FAT, CFT, etc(ELISA, RIA, FAT, CFT, etc

InterferonsInterferons

Low m.wt proteins confer cell ability to resist viral infectionLow m.wt proteins confer cell ability to resist viral infection Host specificHost specific Non specific antiviral activityNon specific antiviral activity

TypesTypesAlpha IF leukocytesAlpha IF leukocytesBeta IF fibroblastBeta IF fibroblastGamma IF lymphocytesGamma IF lymphocytes

Mechanism of interferonsMechanism of interferons

Released IF from infected cellReleased IF from infected cell

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

Endonucleases: degrade RNAEndonucleases: degrade RNA Protein kinases: block initiation of protein synthesisProtein kinases: block initiation of protein synthesis

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Viral VaccinesViral Vaccines•• Traditional approachTraditional approach

prevention rather than cureprevention rather than cure•• great success WHO programgreat success WHO program

eradication of small poxeradication of small pox

Why we use vaccines?Why we use vaccines?•• CheaperCheaper•• ProphylacticProphylactic•• Prevent congenital abnormalitiesPrevent congenital abnormalities•• Control disease and eradicate itControl disease and eradicate it

Types of Viral VaccinesTypes of Viral Vaccines

•• 1. Live attenuated vaccine1. Live attenuated vaccine attenuation for humanattenuation for human

not natural hostnot natural host treated in cell culture mutanttreated in cell culture mutant

e.g. polio virus ; e.g. polio virus ; disadvantage: revertant disadvantage: revertant shelf lifeshelf life2. Killed or inactivated vaccines2. Killed or inactivated vaccines safer than live e.g. Rabiessafer than live e.g. Rabies disadvantage: disadvantage: complete inactivationcomplete inactivation shelf lifeshelf life3. Subunit vaccine3. Subunit vaccine recombinant DNA technologyrecombinant DNA technology production of free N.A vaccine production of free N.A vaccine e.g. HBs Age.g. HBs Ag

Viral chemotherapyViral chemotherapyType of viral infectionsType of viral infections lyticlytic persistentpersistent latentlatent

Antiviral are nucleoside analoguesAntiviral are nucleoside analogues (precursors of DNA or RNA)(precursors of DNA or RNA)•• Acyclovir (zovirax): affect on herpes viruses (inhibit DNA synthesis)Acyclovir (zovirax): affect on herpes viruses (inhibit DNA synthesis)•• Amantadine : treatment of influenza virus (prevent shedding of virus)Amantadine : treatment of influenza virus (prevent shedding of virus)

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•• Ribavirin : treatment of RSV, Lassa fever (inhibit binding of mRNA to Ribavirin : treatment of RSV, Lassa fever (inhibit binding of mRNA to ribosome)ribosome)•• AZTAZT act on reverse transcriptase of HIVact on reverse transcriptase of HIV

ViriodsViriods•• Smallest agentsSmallest agents•• Cause plant diseaseCause plant disease•• Naked, closed circular ss RNANaked, closed circular ss RNA•• Replicate using host cell enzymesReplicate using host cell enzymes•• Not associated with human diseaseNot associated with human disease

PrionsPrions(proteinaceous infectious particles)(proteinaceous infectious particles)•• Cause disease of long i.p.Cause disease of long i.p.•• Neither viruses nor viriodsNeither viruses nor viriods•• Do not have either DNA or RNADo not have either DNA or RNA•• Ability to self replicateAbility to self replicate•• Cause scrapie (CNS dis. of sheep)Cause scrapie (CNS dis. of sheep)•• Resistant to heat & chemicalsResistant to heat & chemicals•• Transmitted to animals by ingestionTransmitted to animals by ingestion•• Neurological transmission has been reportedNeurological transmission has been reported

Prions induced diseasesPrions induced diseases•• KuruKuru fatal neurological diseasefatal neurological disease•• Creutzfeldt-jakob Creutzfeldt-jakob chronic encephalopathychronic encephalopathy ** prions replicate first in lymph tissue brain intracellular ** prions replicate first in lymph tissue brain intracellular

vacuoles spongy like appearancevacuoles spongy like appearance

Prevention & dental implicationPrevention & dental implication•• No treatment or vaccinesNo treatment or vaccines•• Not consuming susceptible foodNot consuming susceptible food•• Disposable equipments in dental practice should be incineratedDisposable equipments in dental practice should be incinerated•• Autoclave instruments at 131 for 18 min.Autoclave instruments at 131 for 18 min.

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