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Structure,Classification of Viruses &laboratory diagnosis of viral infections Assistant Professor & Consultant Virologist College of Medicine & KKUH By: Dr.Malak El-Hazmi

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Properties of Microorganisms Properties of Microorganisms characteristicParasiteFungiBacteriaVirus Cell Yes YesYesYesNo Type of nucleus nucleusEukaryoticEukaryoticProkaryotic----- Nucleic acid Both DNA DNA & RNA Both DNA & RNA Both DNA & RNA DNA or RNA Ribosomes PresentPresentPresentAbsent MitochondriaPresentPresentAbsentAbsent ReplicationMitosis Budding or mitosis Binary fission special

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Characteristics of viruses Acellular organisms Tiny particles Internal coreInternal core Protein coatProtein coat Some Vs have lipoprotein mbSome Vs have lipoprotein mb Obligate intracellular organisms Replicate in a manner diff from cells ( 1V many Vs ) ( 1V many Vs )

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Size ; 20-300 nm

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Viral Structure 1-Viral genome 1-Viral genome2-Capsid 3-Envelope

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Viral Structure 1-Viral genome RNA RNA (Ribonucleic acid) (Ribonucleic acid) All RNA Vs have ss except Reoviruses except Reoviruses single / multiple (+) polarity (-) polarity DNA DNA (Deoxyribonucleic acid) (Deoxyribonucleic acid) All DNA Vs have ds except Parvoviruses except Parvoviruses Single molecule or All Vs are haploid,except retroviruses are diploid

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Viral structure 2-Capsid a protein coat Subunits (capsomeres) Genome (NA) + capsid = nucleocapsid = nucleocapsid Function; Protects NA Protects NA Facilitates its entry into cell Facilitates its entry into cell

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Symmetry based on arrangement of capsomeres Cubic symmetry ( Icosahederal ) ( Icosahederal ) Helical symmetry Elongated (filoviruses) Elongated (filoviruses) Plemorphic( influenza v.) Plemorphic( influenza v.) Complex symmetry poxviruses poxviruses

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Viral structure 3-Envelope Lipoprotein mb (host lipid,virus specific protein ) Budding Envelope is derived from cell mb except herpesviruses from nuclear mb except herpesviruses from nuclear mb Enveloped Vs are more sensitive to heat,dry & ether than nonenveloped Vs heat,dry & ether than nonenveloped Vs Glycoprotein attaches to host cell receptor

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Viral proteins The outer viral ps Mediate attachment to specific Rs Induce neutralizing Abs Target of Abs The internal viral ps Structural ps ( capsid ps of enveloped Vs ) Nonstructural ps ( enzymes) All ssRNA Vs (-) polarity have transcriptase All ssRNA Vs (-) polarity have transcriptase ( RNA dependent RNA polymerase) inside virions ( RNA dependent RNA polymerase) inside virions RetroVs & HBV contain reverse transcriptase RetroVs & HBV contain reverse transcriptase

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Classification of viruses Type of NA The no. of strand The polarity of viral genome of viral genome The presence or absence of envelope absence of envelope Type of symmetry

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Medically Important Viruses ComplexPoxviridae IcosahedralHerpesviridaeHepadnaviridae IcosahedralAdenoviridaePapovaviridae Enveloped RNA DNA Nonenveloped Single-stranded double-stranded IcosahedralParvoviridae Nonenveloped

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HelicalOrthomyxoviridaeParamyxoviridaeRhabdoviridaeFiloviridaeBunyaviridaeArenaviridae HelicalCoronaviridaeIcosahedralTogaviridaeFlaviviridaeRetroviridae IcosahedralReoviridae Enveloped RNADNA Nonenveloped Medically Important Viruses double-strandedSingle-stranded Nonenveloped IcosahedralPicornaviridaeHepeviridaeCaliciviridaeAstroviridae Pos- strand Neg - strand Enveloped

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Replication Adsorption (Attachment) Penetration Uncoating Synthesis of viral components mRNAmRNA Viral proteinsViral proteins NANA Assembly Release Viral growth cycle

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laboratory diagnosis of viral infections Microscopic examination Cell culture Serological tests Molecular method

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Microscopic examination Light microscopy; Histological appearance Histological appearance Ex. Inclusion bodies Ex. Inclusion bodies Owl-eye (CMV) Owl-eye (CMV) Electron microscopy; Morphology& size of virions Ex. Dx of viral GE,rotav., adenov. Dx of skin lesion caused by herpesv, poxv.Dx of skin lesion caused by herpesv, poxv. It is replaced by Ag detection & molecular tests

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Electron micrographs Poxvirus Rotavirus Herpesvirus Adenovirus

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Virus cultivation Laboratory animal Embryonated egg Cell culture

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Cell culture No of sub passages Primary C/C 1 or 2 1 or 2 Diploid C/C [semi continuous] 20 to 50 20 to 50 Continuous cell line Indefinite Indefinite

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Variation in Sensitivity of cell cultures to infection by viruses commonly isolated in clinical virology laboratories Virus Cell culture a PMK HDF HEp-2 RNA virus DNA virus Enterovirus Rhinovirus Influenza virus RSV Adenovirus HSV VZV CMV +++++ +/- + ++++ +- ++++++ ++++++ +++ + +++- - - PMK, primary MK. Degree of sensitivity: +++, highly sensitive;++, moderately sensitive; +, low sensitivity; +/-, variable; -, not sensitive

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Detection of viral growth Cytopathic effects IF Other Uninfected cc Cell rounding Syncytium

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Problems with cell culture ; Problems with cell culture ; Long incubation Sensitivity is variable Susceptible to bacterial contamination Some Vs do not grow in c/c ex. HCV

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Rapid culture technique Shell Vial Assay Detect viral antigens 1-3 days

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Serological test; Antigen detection; sample virus test sample virus test Nasopharyngeal aspirate Influenza V. IF Skin scrapings HSV IF Faeces Rotavirus ELISA Blood HBV( HBsAg ) ELISA

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Serological test; Ex of techniques Complement fixation test (CFT) Immunofluorescence (IF) Enzyme- linked immunosorbent assay (ELISA) Antibody detection;

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Immunofluorescence ; IF A- Direct Ag detection; Ag detection; Sample (Ag) B- Indirect Ab detection; Ab detection; Sample (Ab)

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ELISA Ab detection Ag detection ELISA Ab detection Ag detection Indirect ELISA for Ab detection ; coloured wells indicate reactivity

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Molecular test; Polymerase chain reaction (PCR) Amplification tech. Amplification tech. Viral genome Viral genome Uses; Dx Dx Monitoring response to Rx Monitoring response to Rx

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