Introduction to virology :Introduction to virology By: Dr.Abdalla Ahmed Badri MBBS: O.I.U-MMSC-MALAYSIA


Slide 2:Viruses


Slide 3:OUTLINE introduction to viruses structure and classification basic virology clinical virology


VIROLOGY :VIROLOGY different structure different method of replication implications for diagnosis treatment prevention


CONTROL METHODS :CONTROL METHODS INVOLVE KNOWLEDGE OF: RESERVOIRS MODE OF TRANSMISSION METHODS TO INACTIVATE VIRUS OF INTEREST VACCINES ANTI-VIRAL DRUGS DEVELOPMENT OF DRUG RESISTANCE


EMERGING VIRAL DISEASES :EMERGING VIRAL DISEASES Some North American examples: HIV/AIDS Hantavirus pulmonary syndrome (HPS) West Nile encephalitis (WNV) Severe acute respiratory syndrome (SARS) Monkey pox


Consequences of viral infections :Consequences of viral infections 50% of all absenteeism Children: 7 or more viral infections per year that involve a visit to a physician


Consequences of viral infections :Consequences of viral infections Suffering, followed by recovery Persistent disease Fatal disease Congenital disease Contributory factor in cancer Contributory factor in other diseases


SOME ARE ASYMPTOMATIC! :SOME ARE ASYMPTOMATIC!


VIRUSES CAN BE USEFUL :VIRUSES CAN BE USEFUL VACCINE DEVELOPMENT GENE THERAPY TOOLS TO INVESTIGATE HOST CELLS


WHAT ARE VIRUSES? :WHAT ARE VIRUSES? “A PIECE OF BAD NEWS WRAPPED UP IN A PROTEIN”


Viruses are: :Viruses are: 1. Acellular 2. Obligate intracellular parasites 3. No ATP generating system 4. No Ribosomes or means of Protein Synthesis


Slide 14:* The arenavirus family appears to ‘accidentally’ package ribosomes, but these appear to play no role in protein synthesis.


Viral Classification :Viral Classification 1. Nucleic Acid 2. Morphology 3. Strategy for replication


Viral Structure :Viral Structure 1. Nucleic Acid 2. Capsid (Coat Protein) Nucleic Acid DNA or RNA (But never both) ssDNA ds DNA ss RNA ds RNA


Viral Structure :Viral Structure Capsid (Coat Protein) protects viral genome from host endonucleases capsomeres Binding Sites Envelope derived from the host cell Binding Sites


Slide 20:Viral Morphology 1. Helical


Slide 21:Viral Morphology 2. Polyhedral icosahedral


ICOSAHEDRAL SYMMETRY :ICOSAHEDRAL SYMMETRY 20 faces 12 vertices


ICOSAHEDRAL SYMMETRY :ICOSAHEDRAL SYMMETRY NUCLEIC ACID IS INSIDE


ICOSAHEDRAL SYMMETRY :ICOSAHEDRAL SYMMETRY


ICOSAHEDRAL SYMMETRY :ICOSAHEDRAL SYMMETRY


ICOSAHEDRAL SYMMETRY :ICOSAHEDRAL SYMMETRY = PENTON (pentamer)


ICOSAHEDRAL SYMMETRY :ICOSAHEDRAL SYMMETRY = PENTON


Slide 31:Viral Morphology 3. Enveloped A. Enveloped Helical B. Enveloped Polyhedral


Slide 32:Viral Morphology 4. Complex


5 BASIC TYPES OF VIRAL STRUCTURE :5 BASIC TYPES OF VIRAL STRUCTURE HELICAL ENVELOPED HELICAL ENVELOPED ICOSAHEDRAL COMPLEX ICOSAHEDRAL Adapted from Schaechter et al., Mechanisms of Microbial Disease nucleocapsid icosahedral nucleocapsid nucleocapsid helical nucleocapsid lipid bilayer lipid bilayer glycoprotein spikes = peplomers


CLASSIFICATION NUCLEIC ACID :RNA or DNA segmented or non-segmented linear or circular single-stranded or double-stranded if single-stranded is genome mRNA (+) sense or complementary to mRNA (-) sense CLASSIFICATION NUCLEIC ACID


Slide 35:symmetry icosahedral, helical, complex enveloped or non-enveloped number of capsomers CLASSIFICATION CAPSID


CLASSIFICATION : ENVELOPE REPLICATION STRATEGY CLASSIFICATION


Slide 37:HERPESVIRIDAE HEPADNAVIRIDAE ENVELOPED PAPILLOMAVIRIDAE POLYOMAVIRIDAE (formerly grouped together as the PAPOVAVIRIDAE) CIRCULAR ADENOVIRIDAE LINEAR NON-ENVELOPED DOUBLE STRANDED PARVOVIRIDAE SINGLE STRANDED NON-ENVELOPED POXVIRIDAE COMPLEX ENVELOPED DNA VIRUSES Modified from Volk et al., Essentials of Medical Microbiology, 4th Ed. 1991 All families shown are icosahedral except for poxviruses


Slide 38:FLAVIVIRIDAE TOGAVIRIDAE RETROVIRIDAE ICOSAHEDRAL CORONAVIRIDAE HELICAL ENVELOPED ICOSAHEDRAL PICORNAVIRIDAE CALICIVIRIDAE NONENVELOPED SINGLE STRANDED positive sense BUNYAVIRIDAE ARENAVIRIDAE ORTHOMYXOVIRIDAE PARAMYXOVIRIDAE RHABDOVIRIDAE FILOVIRIDAE SINGLE STRANDED negative sense REOVIRIDAE DOUBLE STRANDED RNA VIRUSES ENVELOPED HELICAL ICOSAHEDRAL NONENVELOPED Modified from Volk et al., Essentials of Medical Microbiology, 4th Ed. 1991


EFFECTS ON HOST :EFFECTS ON HOST MAY INHIBIT HOST DNA, RNA OR PROTEIN SYNTHESIS DETAILS AND MECHANISM VARY


CYTOPATHIC EFFECT :CYTOPATHIC EFFECT ANY DETECTABLE CHANGES IN THE HOST CELL MORPHOLOGICAL CHANGES


Slide 44:Hockley et al. J Gen Virol 69:2455-2469 uninfected HIV infected HIV infected (at higher magnifcation)


CYTOPATHIC EFFECT :CYTOPATHIC EFFECT ANY DETECTABLE CHANGES IN THE HOST CELL MORPHOLOGICAL CHANGES DEATH APOPTOSIS INDEFINITE GROWTH


Growing Viruses :Growing Viruses 1. Bacteriophages Lawn of Bacteria on a Spread Plate Add Bacteriophages Infection will result in “Plaques” Clear zones on plate


Growing Viruses :Growing Viruses Animal Viruses A. Living Animals mice, rabbits, guinea pigs B. Chicken Embryos (Eggs) used to be most common method to grow viruses Still used to produce many vaccines (Flu Vaccine) C. Cell Cultures Most common method to grow viruses today


Cell Cultures :Cell Cultures 1. Primary Cell Lines (monkey) die out after a few generations B. Diploid Cell Lines derived from human embryos lung maintained for up to 100 generations C. Continuous Cell Lines Transformed Cells (Cancerous Cells) may be maintained indefinitly HeLa Cells Henrietta Lax 1951 (Cervical Cancer)


tissue culture cells :tissue culture cells epithelial epithelioid fibroblastic slides from CDC


epithelial cells - adenovirus :epithelial cells - adenovirus uninfected early infection late infection slides from CDC


epithelial cells - adenovirus :epithelial cells - adenovirus uninfected early infection late infection slides from CDC


epithelial cells - respiratory syncytial virus :epithelial cells - respiratory syncytial virus uninfected respiratory syncytial virus slides from CDC


fibroblastic cells - herpes simplex virus :fibroblastic cells - herpes simplex virus uninfected early infection late infection slides from CDC


fibroblastic cells - poliovirus :fibroblastic cells - poliovirus uninfected early infection late infection slides from CDC


Slide 57:PLAQUE ASSAY PLAQUE ASSAY


Slide 58:PLAQUE ASSAY PLAQUE ASSAY


Slide 60:Diluted 10 fold Diluted 100 fold Diluted 1000 fold


PLAQUE FORMING UNIT :PLAQUE FORMING UNIT P.F.U. pfu


SOME POINTS TO REMEMBER :SOME POINTS TO REMEMBER INFECTIVITY NOT EVERY RELEASED PARTICLE IS INFECTIOUS ASSAYS detect every particle (e.g. electron microscope) detect infectious particles only (e.g. plaque assay)


CONSEQUENCES :CONSEQUENCES NO BROAD RANGE ANTIBIOTICS HEAVILY PARASITIC ON HOST CELL NEED TO LOOK FOR WEAK LINK


HOST RANGE :HOST RANGE MAY BE WIDE OR NARROW MAY BE INSECT/ANIMAL, INSECT/PLANT


Slide 66:CYTOPLASM FACTORS AFFECTING HOST RANGE - CELL SURFACE RECEPTORS


FACTORS AFFECTING HOST RANGE :FACTORS AFFECTING HOST RANGE AVAILABILITY OF REPLICATION MACHINERY ABILITY TO GET OUT OF CELL AND SPREAD HOST ANTI-VIRAL RESPONSE CELL SURFACE RECEPTORS


VIRAL STRUCTURE – SOME TERMINOLOGY :VIRAL STRUCTURE – SOME TERMINOLOGY virus particle = virion protein which coats the genome = capsid capsid usually symmetrical capsid + genome = nucleocapsid may have an envelope


Effect of viruses on cells :Effect of viruses on cells Death (lethal-CPE). Transformation (malignant or cancerous). Latent (active state –no obvious effects on the cell’s function). Haemoadsorption (haemagglutinin outer coat adhere to erythrocyte ………agglutinate .


Classification :Classification


Classification :Classification


Classification :Classification


Classification :Classification


Classification :Classification


Classification :Classification


Classification :Classification


Classification :Classification


Physical ,chemical agent and viruses :Physical ,chemical agent and viruses Heat (most at 560 C for 30 min) or at 100 0 C . Cold: low T0 most can be stored (-700 C) Partially inactivated (freezing and thawing ). Drying :variables . Ultraviolet irradiation :inactivates viruses . Chloroform, ether and other organic solvents: Enveloped inactivated, without enveloped resistant .


Physical ,chemical agent and viruses :Physical ,chemical agent and viruses Oxidizing and reducing agents: inactivated by formaldehyde,chlorine,iodine and hydrogen peroxide. Phenols: most relatively resistant. B- propiolactone and formaldehyde : (vaccines) . Virus disinfectants: the best hypochlorite and Glutaraldehyde.


UNCONVENTIONAL AGENTS :UNCONVENTIONAL AGENTS VIROIDS RNA only Small genome Do not code for protein So far, only known viroids are in plants hepatitis delta agent - some viroid, some virus features


UNCONVENTIONAL AGENTS :UNCONVENTIONAL AGENTS PRIONS protein only? do not contain any nucleic acid?