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Introduction to virology for Medical students
The document provides an introduction to virology, defining viruses as obligate intracellular parasites containing either RNA or DNA. It details viral properties, morphology, structure, and the various types of viruses, alongside the basic steps of viral replication. Additionally, it discusses transmission methods and resistance to environmental factors, emphasizing the complexities of viral infections.
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Introduction to virology for Medical students
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- 2. Introduction to Virology •A virus is an obligate intracellular parasite containing genetic material surrounded by protein • Virus particles can only be observed by an electron microscope • Most viruses range in sizes from 20 – 250 nanometers 2
- 3. Viral Properties • Virusesare obligate intracellular parasites • Viruses are non-living entities • Viruses cannot make energy or proteins independent of a host cell (Depends on host cell for replication) • Viral genome are either RNA or DNA but not both. • Viruses have a naked capsid or envelope with attached proteins • Do not possess cellular organization • Viruses do not have the genetic capability to multiply by division. • They are NOT cultiviable on ordinary media.
- 4. Cellular Acellular Prokaryotes EukaryotesViruses Bacteria and archaea Fungi,algae,protozoa, helminths Viruses and bacteriophage s Types of Microbes (b) VirusTypes Bacterial virus AIDS virus Envelope Capsid Nucleic acid (a) Cell Types Prokaryotic Chromosome Ribosomes Flagellum Cellwall Cell membrane Eukaryotic Flagellum Mitochondria Ribosomes Cell membrane Nucleus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
- 5. 5 Morphology - Size •Much smaller than bacteria • “Filterable agents” – can pass through filters that can hold back bacteria • Vary widely in size: – Largest – poxvirus (300nm) – Smallest – parvovirus (20nm)
- 6. Viruses are Ultramicroscopic Konemanet al. Color Atlas and Textbook of Microbiology 5th Ed. 1997 6
- 7. Shape of Viruses •Spherical • Rod-shaped • Brick-shaped • Tadpole- shaped • Bullet-shaped • Filament-shaped
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- 14. 14 VIRAL STRUCTURE –SOME TERMINOLOGY • virus particle = virion • protein which coats the genome = capsid • capsid usually symmetrical • capsid + genome = nucleocapsid • may have an envelope
- 15. Virion • The complete infectiousunit of virus particle 15
- 16. Viral Structure -Overview Fig 1. Schematic overview of the structure of viruses ** does not exist in all viruses Nucleic acid Nucleocapsid Capsid Viral envelope** Envelope protein Membrane protein Spike protein
- 17. Basic virus structure Capsid protein Nucleocapsid Nakedcapsid virus DNA RNA or = + Nucleocapsid Lipid membrane, glycoproteins Enveloped virus +
- 18. Medic White, DO andFenner,FJ. al Virology, 4th Ed. 1994 Virus particle = virion
- 19. Viral genome • Viralgenome comprises viral nucleic acid genome (DNA or RNA). Controls viral heredity and variation and responsible for the infectivity. √ DNA: either double stranded (ds) or single stranded (ss); : either linear or circular √ RNA: either double stranded (ds) or single stranded (ss); : either linear or circular : ds RNA viruses: always linear : ss RNA viruses: either segmented or non- segmented : ss RNA viruses: + sence(mRNA) or –sence (strand complementary to mRNA)
- 20. HERPESVIRIDAE HEPADNAVIRIDAE ENVELOPED PAPILLOMAVIRIDAE POLYOMAVIRIDAE (formerly grouped togetheras the PAPOVAVIRIDAE) CIRCULAR ADENOVIRIDAE LINEAR NON-ENVELOPED DOUBLE STRANDED PARVOVIRIDAE SINGLESTRANDED NON-ENVELOPED POXVIRIDAE COMPLEX ENVELOPED DNA VIRUSES All families shown are icosahedral except for poxviruses Dr . T . VM.RoadoifiMedDfromVolk et al., Essentials of Medical Microbiology, 4th Ed. 1 9 49 81
- 21. FLAVIVIRIDAE TOGAVIRIDAE RETROVIRIDAE ICOSAHEDRAL CORONAVIRIDAE HELICAL ENVELOPED ICOSAHEDRAL PICORNAVIRIDAE CALICIVIRIDAE ASTROVIRIDAE NONENVELOPED SINGLESTRANDED positivesense ORTHOMYXOVIRIDAE PARAMYXOVIRIDAE RHABDOVIRIDAE FILOVIRIDAE BUNYAVIRIDAE ARENAVIRIDAE SINGLESTRANDED negativesense REOVIRIDAE DOUBLE STRANDED RNA VIRUSES ENVELOPED HELICALICOSAHEDRAL NONENVELOPED Dr . T . VM.RoadoifiMedDfromVolk et al., Essentials of Medical Microbiology, 4th Ed. 1 9
- 22. Viral Capsid • Capsid– the protein coat surrounding the nucleic acid core. It – protects nucleic acid from inactivation – helps to introduce viral genome into host cell • Capsomers - the repeating protein subunits that make up the capsid • Protomers – the polypeptide chains which make up the capsomers 1. Protomers 2. Capsomers 3. Pro-Capsid 4. Mature Capsid
- 23. Symmetry of Nucleocapsid – Cubic(Icosahedral) • a polygon with 12 corners (vertices) & 20 sides (facets), each an equilateral triangle. • Eg. adenovirus – Helical • Protein binds around DNA/RNA in a helical fashion • eg. Coronavirus – Complex • Is neither cubic nor helical eg. poxvirus ICOSAHEDRAL SYMMETRY HELICAL SYMMETRY COMPLEX SYMMETRY POXVIRUS FAMILY
- 24. Envelope • A lipid-containingmembrane that surrounds capsid. • It is acquired during viral maturation by a budding process through a cellular membrane. • viruses can be divided into 2 kinds: enveloped virus and naked virus. Enveloped icosahedral virus Enveloped helical virus
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- 26. 5 BASIC TYPESOF VIRAL STRUCTURE HELICAL ENVELOPED HELICAL ENVELOPED ICOSAHEDRAL ICOSAHEDRAL nucleocapsid icosahedral nucleocapsid helical nucleocapsid lipid bilayer COMPLEX nucleocapsid lipid bilayer glycoprotein spikes = peplomers Adapted from Schaechter et al., Mechanisms ofMicD rr o. T b. V i. aR a loDMisDease
- 27. • ADSORPTION • PENETRATION •UNCOATING AND ECLIPSE • SYNTHESIS OF VIRAL NUCLEIC ACID AND PROTEIN • ASSEMBLY (maturation) • RELEASE BASIC STEPS OF VIRAL REPLICATION
- 28. VIRAL REPLICATION Stages invirus replication begin when virion infects host cells 1 Virus attachment and entry 2 Uncoating of virion Migration of genome nucleic acid to nucleus 4 Synthesis of viral nucleic acid and protein. 5 Virion assembly 6 Release of new virus particles
- 29. Chemical Properties -Resistance Temperature: Enveloped viruses are more heat-labile Inactivated at 560C-30’ (exception- HBV) and few sec at 1000C. Some may be preserved by lyophilization pH: . stable between pH 5 and 9 Enteroviruses – resistant to acidic conditions
- 30. Radiation: UVand ionising radiation inactivates viruses Photodynamic Inactivation Vital dyes- Toluidene blue Disinfectants Most viruses are destroyed by oxidising agents such as chlorine, iodine and hydrogen peroxide. However, majority of viruses are resistant to phenol; chlorination does not always inactivate enteroviruses or hepatitis viruses, particularly if present with organic or faecal material.
- 31. Transmission of Viruses •Respiratory transmission – Influenza A virus • Faecal-oral transmission – Enterovirus • Blood-borne transmission – Hepatitis B virus • Sexual Transmission – HIV • Animal or insect vectors – Rabies virus
- 32. Viruses enter thebody of the host in a variety of ways, for example...
- 33. The commonest formsof transmission are via... INHALED DROPLETS in sneezing of coughing for example the COMMON COLD or INFLUENZA VIRUSES.
- 34. or by... drinking wateror eating raw food, for example, HEPATITIS A and POLIOVIRUS.
- 35. The commonest formsof transmission are also via... sexual intercourse for example HIV and HEPATITIS B and...
- 36. also... vertical transmission - frommother to baby for example HIV, HEPATITIS B and RUBELLA...
- 37. also... •bites of vectorarthropods such as mosquitoes for example YELLOW FEVER, and DENGUE.
- 38. Most viral infections... donot lead to such serious complications and the host...
- 39. get well aftera period of sickness to be immune for the rest of their lives. Examples are MEASLES INFECTION, RUBELLA or German measles, MUMPS and many others...
- 40. Embryonated Egg Cell Lines/Tissue cultures Animal inoculation Chorioallantioc membrane (CAM) Allantoic cavity Amniotic cavity Yolk Sac Primary Diploid/ Secondary Continuous Suckling mice Virus Culture
Editor's Notes
- #5 Microbiology: A Systems Approach