Basic Virology and Medical Mycology PDF

INTRODUCTION TO VIROLOGY Asmaa Omar Professor of Clinical Pathology- Faculty of Medicine- Assiut University  Types of Microbes Cellular Acellular...

INTRODUCTION TO VIROLOGY Asmaa Omar Professor of Clinical Pathology- Faculty of Medicine- Assiut University  Types of Microbes Cellular Acellular Prokaryotes Eukaryotes Viruses (a) Cell Types (b) VirusTypes Prokaryotic Eukaryotic Nucleus Mitochondria Chromosome Envelope Ribosomes Capsid Ribosomes Nucleic acid AIDS virus Cellwall Cell membrane Flagellum Flagellum Cell membrane Bacterial virus Bacteria and archaea Fungi,algae,protozoa, Viruses and helminths bacteriophages Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  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 3  Viral Properties Viruses are 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.  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) 5 Viruses are Ultramicroscopic Koneman et al. Color Atlas and Textbook of Microbiology 5th Ed. 1997 6 Shape of Viruses Spherical Rod-shaped Brick-shaped Tadpole- shaped Bullet-shaped Filament-shaped Spherical Rod-shaped. Brick-shaped Tadpole-shaped Bullet-shaped Filament-shaped  VIRAL STRUCTURE – SOME TERMINOLOGY virus particle = virion protein which coats the genome = capsid capsid usually symmetrical capsid + genome = nucleocapsid may have an envelope 14  Virion The complete infectious unit of virus particle 15  Viral Structure - Overview Nucleic acid Nucleocapsid Capsid Envelope protein Viral envelope** Membrane protein Spike protein Fig 1. Schematic overview of the structure of viruses ** does not exist in all viruses Basic virus structure DNA Capsid Naked capsid or + Nucleocapsid = protein virus RNA Lipid membrane, Nucleocapsid + Enveloped virus glycoproteins Virus particle = virion White, DO and Fenner, FJ. Medic al Virology, 4th Ed. 1994  Viral genome Viral genome 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  DNA VIRUSES DOUBLE STRANDED SINGLE STRANDED COMPLEX NON-ENVELOPED ENVELOPED ENVELOPED NON-ENVELOPED PARVOVIRIDAE POXVIRIDAE HERPESVIRIDAE HEPADNAVIRIDAE CIRCULAR LINEAR PAPILLOMAVIRIDAE ADENOVIRIDAE All families shown are POLYOMAVIRIDAE icosahedral except for (formerly grouped together as the poxviruses PAPOVAVIRIDAE) Dr.T.VM.RoadoifiMedDfromVolk et al., Essentials of Medical Microbiology, 4th Ed. 194981  RNA VIRUSES SINGLE STRANDED SINGLE STRANDED DOUBLE positive sense negative sense STRANDED ENVELOPED NONENVELOPED ENVELOPED NONENVELOPED ICOSAHEDRAL HELICAL ICOSAHEDRAL HELICAL ICOSAHEDRAL FLAVIVIRIDAE CORONAVIRIDAE PICORNAVIRIDAE ORTHOMYXOVIRIDAE REOVIRIDAE TOGAVIRIDAE CALICIVIRIDAE PARAMYXOVIRIDAE RETROVIRIDAE ASTROVIRIDAE RHABDOVIRIDAE FILOVIRIDAE BUNYAVIRIDAE ARENAVIRIDAE Dr.T.VM.RoadoifiMedDfromVolk et al., Essentials of Medical Microbiology, 4th Ed. 19  Viral Capsid Capsid – the protein coat 1. Protomers surrounding the nucleic acid core. It protects nucleic acid from inactivation helps to introduce viral genome into host cell 4. Mature Capsid Capsomers - the repeating protein subunits that make up the capsid Protomers – the polypeptide chains which make up the capsomers 2. Capsomers 3. Pro-Capsid Symmetry of Nucleocapsid – Cubic (Icosahedral) a polygon with 12 corners (vertices) & 20 sides ICOSAHEDRAL SYMMETRY (facets), each an equilateral triangle. Eg. adenovirus – Helical Protein binds around DNA/RNA in a helical fashion eg. Coronavirus – Complex HELICAL SYMMETRY Is neither cubic nor helical eg. poxvirus POXVIRUS FAMILY COMPLEX SYMMETRY Envelope A lipid-containing membrane that surrounds capsid. It is acquired during viral maturation by a budding process through a cellular Enveloped icosahedral virus membrane. viruses can be divided into 2 kinds: enveloped virus and naked virus. Enveloped helical virus Cubic Helical Non- Enveloped Virus Enveloped Virus  5 BASIC TYPES OF VIRAL STRUCTURE icosahedral nucleocapsid nucleocapsid lipid bilayer ICOSAHEDRAL ENVELOPED ICOSAHEDRAL helical nucleocapsid COMPLEX nucleocapsid lipid bilayer glycoprotein spikes = peplomers HELICAL ENVELOPED HELICAL Adapted from Schaechter et al., Mechanisms of MicDrro.Tb.Vi.aRaloDMisDease