Lecture 2b: General Methodologies of Viral Research

1. Pathogen versus Toxin Problem
   1. Koch's Postulates for bacteria
   2. River's Postulates for viruses

2. Classification of Viruses: a working taxonomy based upon the biochemical properties of the viral particles.* (Fill in the names of viruses as you encounter them in the course.)

   	dsDNA.........	ssDNA.........	ssRNA.........	dsRNA.........
   bacteria.........
   animals
   plants

3. Viral Manifestations: plaques, lesions, tumors, inclusion bodies

4. The VIRION - the infective unit or plaque forming unit (pfu)
   1. A look at a prototype bacterial virus (aka: bacteriophage, which means "eater of bacteria")

      

   2. Sizing the Infective Units
      1. Then
      2. Now
   3. Titration
      1. The number of particles which equal 1 pfu ("eop")
         Plot the plaque counts versus the relative concentrationŠ (classic dose plot)
      2. Modern Titration methods
         1. Bacteriophages
         2. Animal Viruses
         3. Plant Viruses

5. Inactivation of Viruses
   1. Chemical Agents - Nitrous acid (HNO2), Formalin, Pseudouridine, Enzymatic degradation, detergents
   2. Physical Agents
      1. Heat
      2. Photons
         1. Ionizing radiation (x-rays and gamma-rays)
         2. Ultraviolet (Dulbecco and thymine-thymine dimers)
            1. Photoreactivation
            2. Dark Repair
            3. Para-sexual reconstitution
         3. Dose plots and their implications
         4. Action Spectra (Sidney Y. Wang)

---

* This is a prevailing taxonomic scheme for classifying viruses: