5) Introduction to Viruses ( medical 2024-1446).pdf

( Foundation Block , Microbiology : 2024-1446) By: Dr.Malak El-Hazmi Associate professor Consultant Medical Microbiologist College of Medicine & King Saud University M...

( Foundation Block , Microbiology : 2024-1446) By: Dr.Malak El-Hazmi Associate professor Consultant Medical Microbiologist College of Medicine & King Saud University Medical City  OBJECTIVES Ø Distinguish the viruses from other microorganisms Ø General characteristics of viruses. Ø Structure of viruses. Ø Classification of viruses. Ø Steps of virus replication. Ø laboratory diagnosis of viral infections.  Properties of Microorganisms characteristic Parasites Fungi Bacteria Viruses Cell Yes Yes Yes No Type of Eukaryotic Eukaryotic Prokaryotic ----- nucleus Nucleic acid Both Both Both DNA or DNA DNA DNA RNA & RNA & RNA & RNA Ribosomes Present Present Present Absent Mitochondria Present Present Absent Absent Replication Mitosis Budding or Binary fission special mitosis  Characteristics of viruses Ø Tiny particles Internal core Protein coat Some Vs have lipoprotein mb Ø Acellular organisms Ø Obligate intracellular organisms Ø Replicate in a manner diff from cells ( 1V many Vs ) Size ; 20-300 nm  Viral Structure 1-Viral genome 2-Capsid 3-Envelope  Viral Structure 1-Viral genome DNA or RNA (Deoxyribonucleic acid) (Ribonucleic acid) Ø All DNA Vs have ds Ø All RNA Vs have ss except Parvoviruses except Reoviruses Ø Single molecule Ø single / multiple Ø (+) polarity Ø (-) polarity All Vs are haploid ,except retroviruses are diploid  Viral structure 2-Capsid Ø a protein coat Ø Subunits (capsomeres) Ø Genome (NA) + capsid = nucleocapsid Ø Function; l Protects NA l Facilitates its entry into cell  Symmetry based on arrangement of capsomeres Ø Cubic symmetry ( Icosahederal ) Ø Helical symmetry Ø Complex symmetry  Symmetry based on arrangement of capsomeres Ø 1-Cubic symmetry ( Icosahedral ) Adenovirus Herpesvirus  Symmetry based on arrangement of capsomeres Ø 2- Helical symmetry Elongated Pleomorphic (filoviruses) ( influenza v.) Ø 3- Complex symmetry poxviruses  Viral structure 3-Envelope Lipoprotein mb (host lipid ,virus specific protein ) Ø Budding Ø Envelope is derived from cell mb except herpesviruses from nuclear mb Ø Enveloped Vs are more sensitive to heat ,dry & ether than nonenveloped Vs Ø Glycoprotein attaches to host cell receptor  Viral proteins v The outer viral ps Ø Mediate attachment to specific Rs Ø Induce neutralizing Abs Ø Target of Abs v The internal viral ps Ø Structural ps ( capsid ps of enveloped Vs ) Ø Nonstructural ps ( enzymes) l All ssRNA Vs (-) polarity have transcriptase ( RNA dependent RNA polymerase) inside virions l RetroVs & HBV contain reverse transcriptase  Classification of viruses Ø Type of NA* Ø The no. of strand Ø The polarity of viral genome Ø The presence or absence of envelope Ø Type of symmetry  Medically Important Viruses DNA RNA Single-stranded double-stranded Enveloped Nonenveloped Nonenveloped Icosahedral Complex Icosahedral Icosahedral Poxviridae Herpesviridae Adenoviridae Parvoviridae Papillomaviridae Hepadnaviridae Polyomaviridae  Medically Important Viruses DNA RNA Single-stranded double-stranded Neg - strand Pos- strand Nonenveloped Enveloped Icosahedral Helical Enveloped Nonenveloped Reoviridae Orthomyxoviridae Helical Paramyxoviridae Coronaviridae Icosahedral Rhabdoviridae Icosahedral Picornaviridae Filoviridae Togaviridae Hepeviridae Bunyaviridae Flaviviridae Caliciviridae Arenaviridae Retroviridae Astroviridae  OBJECTIVES Ø Distinguish the viruses from other microorganisms Ø General characteristics of viruses. Ø Structure of viruses. Ø Classification of viruses. Ø Steps of virus replication. Ø laboratory diagnosis of viral infections.  Replication Ø Adsorption (Attachment) Ø Penetration Ø Uncoating Ø Synthesis of viral components mRNA Viral proteins NA Ø Assembly Ø Release Viral growth cycle  Adsorption Ø Attachment site ; ex- glycoprotein fiber  Penetration 1-Fusion 2-Endocytosis Ø Viral envelope (enveloped Vs ) fuses with endosome mb Ø Nonenveloped V. lysis ,pore  Replication Ø Adsorption (Attachment) Ø Penetration Ø Uncoating Release of viral genome - cytoplasm - nucleus  Synthesis of viral components Ø mRNA Viral genome transcription mRNA +ssRNA acts directly Ø Viral proteins mRNA translation viral proteins cell ribosome - enzymes - structural ps Ø replication of viral genome  Replication Ø Adsorption (Attachement) Ø Penetration Ø Uncoating Ø Synthesis of viral components mRNA Viral proteins NA ØAssembly NA + V. proteins = Virions Ø Release  Release Ø 1-Budding Ø 2- Cell lysis (enveloped Vs) or rupture -cell mb* (nonenveloped) -nuclear mb (herpesVs)  Replication Ø Adsorption (Attachment) Ø Penetration Ø Uncoating Ø Synthesis of viral components mRNA Viral proteins NA Ø Assembly Ø Release Viral growth cycle  laboratory diagnosis of viral infections Ø Microscopic examination. Ø Cellculture. Ø Serological tests. Ø Detection of viral Ag. Ø Molecular method.  Microscopic examination Ø Light microscopy; Histological appearance Ex. Inclusion bodies Owl’s eye (CMV) Ø Electron microscopy; l Morphology& size of virions l Ex. Dx of skin lesion caused by herpesv, poxv. l It is replaced by Ag detection & molecular tests Ø Electron micrographs Herpesvirus Poxvirus Virus cultivation Ø Laboratory animal Ø Embryonated egg Ø Cell culture Cell culture C/C) 1-Primary C/C 2-Diploid C/C [semi continuous] 3-Continuous cell line Variation in Sensitivity of cell cultures to infection by viruses commonly isolated in clinical virology laboratories Cell culturea Virus PMK HDF HEp-2 RNA virus Enterovirus +++ ++ +/- Rhinovirus + +++ + Influenza virus +++ + - RSV ++ + +++ DNA virus Adenovirus + ++ +++ HSV + ++ ++ VZV + +++ - CMV - +++ - PMK, primary MK. Degree of sensitivity: +++, highly sensitive;++, moderately sensitive; +, low sensitivity; +/-, variable; -, not sensitive  Detection of viral growth Ø Cytopathic effects Uninfected cc Cell rounding Syncytium Ø Others Problems with cell culture ; Ø Long incubation Ø Sensitivity is variable Ø Susceptible to bacterial contamination Ø Some Vs do not grow in c/c ex. HPV  Rapid culture technique Ø Shell Vial Assay Ø Detect viral antigens Ø 1-3 days  Serological test; Antigen detection; sample virus test Ø Skin scrapings HSV IF Ø Blood HBV(HBsAg) ELISA  Serological test; Antibody detection; Ø Ex of techniques l Immunofluorescence (IF) l Enzyme- linked immunosorbent assay (ELISA) Immunofluorescence ; IF Ø A- Direct Ag detection; l Sample (Ag) Ø B- Indirect Ab detection; l Sample (Ab)  ELISA Ab detection Ag detection Indirect ELISA for Ab detection ; coloured wells indicate reactivity  Molecular test; Ø Polymerase chain reaction (PCR) l Amplification tech. l Viral genome Ø Uses; l Dx l Monitoring response to Rx  OBJECTIVES Ø Distinguish the viruses from other microorganisms Ø General characteristics of viruses. Ø Structure & symmetry of viruses. Ø Classification of viruses. Ø Steps of virus replication. Ø laboratory diagnosis of viral infections.