VIROLOGY – The Study of Viruses

Are NOT Small BacteriaAre NOT Living CellsLack ALL (nearly) enzymes necessary for metabolism

and biosynthesis

ARE Protein Coat surrounding Nucleic AcidARE Obligate Intracellular ParasitesAre Important PathogensCause Diseases that are difficult to treat

Examples: Colds, Flu, Measles, Mumps, Variolla (Chick. Pox) Small Pox, Polio, Encephalitis, Cancer (Oncogenic Viruses)

Duh

A Little History

Pasteur – Treated RabiesJenner - Treated Small Pox

Vaccines – Prevention, NOT CURE

1949 – Culture Polio Virus in Tissue Culture Animal Viruses grow in Animal Cells

1950 – Electron Microscope Invented Needed to SEE Viruses

Still Discovering Viruses

Oral Polio vaccine

Distribution 1962

General Concepts

Size – 20 –300 nannometers (0.02 - .3 um)Contain: “Core” of Nucleic Acid

(either DNA - 1 or 2 stranded)(or RNA – 1 or 2 stranded)

Protein Coat surrounds Core

Must use Host Cell Metabolic Machinery to Replicate and Produce More Viral Particles

ARE OBLIGATE INTRACELLUAR PARASITES

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Viral Classification

Original (and still) by disease they cause

International Committee on the Taxonomy of Viruses1. Nucleic acid type )DNA/RNA2. Replication type3. Morphology

OtherCapsid symmetry icosahedral, helical, complexEnveloped or not + or -Ether Sensitivity + or -

Lytic Cycle of Bacteriophage

Lytic Cycle of Bacteriophage

One Step Viral “Growth” Curve

Lysogenic Cycle of Bacteriophage

Retroviridae

HIV-1

Reverse Transcriptase

RNA-DependentDNA- Polymerase

Provirus

Cultivation of Viruses

1. In Living Animals or Bacteria2. In Embryonated Chick eggs3. In Tissue Culture – Primary

Permanent - HeLa Cells

Viral Effects1 Lysis of Cells and Death Polio Virus

2 Form Inclusion Bodies - Rabies Negri Bodies - clumped viral parts

3 Alter Cells a. Cells Proliferate – Poxviridae b. Fuse Cell Membranes – Herpes, Measles (Giant Cells) c. Persistent Infections

Viral Latency – Herpes simplex, cold sores, Chicken PoxChronic – Hepatitus B shed virus but not have diseaseSlow Viral Infection – SSPE

4 Transformation – Normal to Malignant Cell a. DS-DNA – Papoviridae (cervical), Herpesviridae (EB) (nasop) b. SS-RNA – Retroviridae HTLV (leukemia), Rous Sarcoma Virus src gene – mammary tumors in animals (?humans)

Viral Congenital Effect

Vertical Transmission Rubella – teratogenic (by slowed growth rate)

rubella syndrome – birth defects if in 1st trimester HIV vertical transmission

Cell Responses Antibody Formation Interferon Production –

Protein released at infection siteProtects adjacent cells

Prions – Infectious ProteinKuru – Fore People of New Guinea – cannibalsScrapie in sheep – proposed protein diseaseSpongiform EncephelopathyCreutzfeldt-Jacob Disease (CJD)

Mad Cow Disease (BSE) – origin?, pass to Humans