Lecture 12 Virology

Viruses, Viroids, and Prions

I. General characteristics of viruses (non-living, obligate, intracellular pathogens)

     They can infect every domain of living organism, but are limited to that specific host e.g. bacteriophages can only infect bacteria, not humans cells.  Bacteriophages are simplest (infecting prokaryotic cells) and best understood and therefore act as models.    

A. Components       

                1. Protein coat

                    a. protection

                    b. attachment

                    c. identity

                    d. immunity

                2. Envelop

                    a. lipid bilayer

                    b. attachment spikes

                3. Genome

                    a. only DNA or RNA

                    b. DNA - linear or circular, double or single stranded

                    c. RNA single or double stranded

     

 B. Replication Cycle

               

Examples of lysogenic bacteria:

Corynebacterium diphtheriae - only the lysogenic form is pathogenic

Streptococcus pyogenes - lysogenic form causes scarlet fever

                3. Implications of viral genome and replication cycles

                            a. Lytic cycles cause acute infections common to viral diseases that are familiar e.g. chickenpox, measles, etc.

                            b. proviruses can increase virulence

                            c. lysogenic viruses can be responsible for latent diseases, slow diseases, cancer

II. Classification of viruses - http://www.tulane.edu/~dmsander/Big_Virology/BVHomePage.html

http://www.virology.net/garryfavweb.html

        A. By host cells - bacteria, animals, plants (and occasionally symptoms)

        B. Genome - DNA (single, double) RNA (single stranded, double stranded, multiple RNA's - see influenza virus)

        C. Shape & envelope

III. Culturing Viruses

        A. Must be living cells, maintained in an aseptic environment

                1. eggs

                2. cell culture (continuous lines)

IV. Diagnosing viral diseases -

        A. Monolayers and CPE cytopathic effect

figure a. Monolayer of normal fetal tonsil cells, b. tonsil cells with adenovirus, c. tonsil cells with herpes simplex infection and monolayer destroyed

        B. Viral plaques

        C. Electron micrographs

           

V. Persistent and Slow infections

        A. Viroids - single naked RNA capable of infecting a cell -

      B. Prions - Proteinaceous infectious particles - thought to be "self-replicating" but only DNA does this. Prions

      C. Tumorogenic viruses -

Viruses that are known causes of cancer have been DS DNA. However now HIV is known to be instrumental in several cancers including Kaposi's sarcoma

benign vs malignant

tumor, neoplasm, metastasis

http://www.tulane.edu/~dmsander/Big_Virology/BVHomePage.html

VI. Emerging viral infections

During the past 15 years, Nine viral infections or prion pathogens have

emerged as substantial public health threats:

  1. HIV

  2. the hepatitis C virus

  3. hantaviruses

  4. the agent of bovine spongiform encephalopathy (BSE)/variant Creutzfeldt±Jakob disease(CJD)

  5. the West Nile virus

  6. Ebola virus
    and three relatively newly identified herpesviruses ±human herpesvirus

  7. (HHV)-6

  8. HHV-7

  9. HHV-8.

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