Replication of Viruses: An Overview

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General properties of viruses
Instructor Behzad Khansarinejad Dept. of Medical
Virology, Tarbiat Modarres University
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Evolutionary Origin of Viruses

• Viruses may be derived from DNA or RNA nucleic
  acid components of host cells that became able to
  replicate autonomously and evolve independently.
• Viruses may be degenerate forms of intracellular
  parasites
• Viruses may be the first form of the living
  material
• May be they come from another planet !?

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Classification of Viruses

• Virus family names have the suffix -viridae
• Genus names carry the suffix virus
• In four families (Poxviridae, Herpesviridae,
  Parvoviridae, Paramyxoviridae), a larger grouping
  called subfamilies has been defined( - Virinae)
• Virus orders may be used to group virus families
  that share common characteristics(
  mononegavirales, Nidovirales)

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Cubic symmetry (Icosahedral )
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Helical Symmetry
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Measuring the Sizes of Viruses

• Direct Observation in the Electron Microscope
• Sedimentation in the Ultracentrifuge
• Comparative Measurements

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Virus Genomes
Single Stranded
DNA
Double Stranded
Nucleic Acid
Double Stranded
Positive
RNA
Single Stranded
Negative
RNA
DNA
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Reaction to Physical Chemical Agents

• Heat Cold
• Stabilization of Viruses by Salts
• pH
• Radiation
• Photodynamic Inactivation
• Ether Susceptibility
• Detergents
• Formaldehyde
• Antibiotics Other Antibacterial Agents

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Replication of Viruses An Overview

• Attachment

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• Penetration or Engulfment

• Receptor-mediated endocytosis ( Viropexis)
• Fusion
• Direct penetration of virus particles across the
  plasma membrane
• (Translocation)

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endocytosis ( Viropexis)
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Fusion
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Direct penetration
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• Uncoating
• Eclipse period
• Expression of Viral Genomes and Synthesis of
  Viral Components
• Assembly
• Release

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Techniques used for Detection of Viruses

• Electron microscopy
• 2. Serological assays ( ELISA, IF, CF, NT, RIA)
• molecular assays ( PCR, RT-PCR, NASBA, Real
  Time-PCR)
• Viral cultivation

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PCR Principles
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Hosts for Virus Cultivation
Laboratory Animals Embryonated Chicken
Eggs Cell Culture
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Laboratory Animals
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Embryonated Chicken Eggs
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Cell culture
Primary Cell Culture Cell Strains Cell Lines
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Primary Cell Culture
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Subculture
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Detection of Virus-Infected Cells
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Inclusion bodies
Negri bodies in a rabies infected cell