An Introduction to the Viruses

1. An Introduction to the Viruses Chapter 6

2. Virus = (L. poison) Non-cellular infectious particles Non-living active or inactive Genetic parasites Use host cell machinery to replicate DNA or RNA Infect all types of cells Bacteria Algae Fungi Protozoa Plants Animals Viruses“obligate intracellular parasites” Poxvirus Ebola Virus Vaccinia Virus

3. Smallest infectious agents (< 0.2 m) Parvoviruses (respiratory infections) = 20 nm Poxviruses (smallpox) = 250 nm 2000 viruses/bacterial cell 50 million/human cell Viruses = Ultramicroscopic

4. Virion = infectious extracellular particle Capsid = outer coating Nucleocapsid = nucleic acid + capsid Viral Terminology

5. Naked vs Enveloped Viruses • Envelope = modified host cell membrane • Spikes or peplomers = attachment of virus • Pleiomorphic due to flexible envelope

6. Encloses & protects nucleic acid (DNA & RNA) Composed of identical protein subunits = capsomers 2 types: helical iscosahedral Capsid = Protein Coat

7. Rod-shaped capsomers form helix DNA or RNA = coiled inside Naked helical (rigid) Tobacco mosaic virus Enveloped helical (flexible) Influenza Measles Rabies Helical Capsids

8. Naked Papillomavirus (warts) Enveloped Herpes simplex (cold sores) 20-sided with 12 corners Vary in # of capsomers Poliovirus (32) Adenovirus (240) Capsid = sphere or cube Icosahedral Capsids

9. Poxvirus Herpesvirus Mumps Virus Adenovirus Phage Rhabdovirus HIV Papillomavirus Fig. 6.10

10. DNA or RNA Single or double-stranded Virus = genetic parasite Hepatitis B: 4 genes E. coli: 4000 genes Human: 40,000 genes Carry genes for: Viral capsid Genetic material Host regulation Viral packaging Viral Core

11. Latin root (descriptive) plus -viridae Family name ends in -viridae (Herpesviridae) Genus name ends in -virus (Varicellovirus) Common name (Chickenpox) Capsid type (helical or icosahedral) Enveloped or naked DNA (6 families) or RNA (13 families) Host cell (bacterial, plant or animal) Size & shape Rhabdovirus = bullet-shaped Togavirus = cloak-like Adenovirus = infect adenoids Lentivirus = slow, chronic infection Picornavirus = small RNA Reoviruses = respiratory, enteric viruses Classifying & Naming Viruses

13. DNA Viruses Poxviruses (smallpox) Herpesviruses Hepatitis B virus Papillomavirus (warts) Adenoviruses RNA Viruses Poliovirus Rhinovirus (colds) West Nile virus Influenza virus Mumps Measles Rabies HIV (retrovirus) DNA vs RNA Viruses Important thing here is that both DNA and RNA viruses exist

14. Adsorption (specific, mediated by receptors, much of the time by receptor-mediated endocytosis) Penetration & uncoating of genome Duplication/synthesis Assembly (also called maturation) Release (budding, lysis) Animal Virus Replication

15. Host Range • Tropism = Spectrum of cells a virus can infect • cell has specific structure (receptor) on its surface for viral attachment • HIV-1 (CD4 and chemokine receptor) • Epstein-Barr Virus (complement protein, CR2) • SARS (ACE-2 = angiotensin converting enzyme) • cell has to contain enzymes & materials needed to produce new virions • May be one species or many • HIV (only humans) vs rabies (many animals) • May be one tissue or many within a host • Hepatitis (liver) vs polio (intestinal & nerve cells)

16. Phage Movie

17. Retrovirus Movie

18. Coronavirus (SARS) Adenovirus Adsorption

19. Viral Penetration Herpesvirus:Endocytosis Mumps Virus: Fusion

20. 2 Mechanisms of EntryMovie

21. Release by Budding • Budding occurs by exocytosis • Virions are slowly shed from cell • Pox-infected cell releases 3000-4000 virions • Poliovirus-infected cell releases 100,000 virions

22. Changes in size & shape Nuclear & cytoplasmic inclusion bodies Cells fuse to form multinucleated cells Cell death & lysis Alter DNA Oncoviruses: transform cells into cancerous cells Epstein-Barr virus (lymphoma) Papillomavirus (cervival cancer) HTLV (leukemia) Persistent infections: last weeks to years Chronic latent state: Herpes (cold sores & genital herpes) Varicella-Zoster (chickenpox & shingles) Cytopathic Effects:Virus-Induced Damage to Cells

23. Live animals (In vivo) Bird embryos (chicken & duck) intact self-supporting unit sterile self-nourished 3. Cell culture (In vitro) Growing Animal Viruses

24. Infection & Plaque Formation • Plaques = areas where virus-infected cells undergo lysis

25. Prions: misfolded proteins contain no nucleic acid cause spongiform encephalopathies = holes in the brain common in animals Sheep & goats (Scrapie) Cattle (Mad cow disease) Humans – Creutzfeldt-Jakob Disease (beef) & Kuru (cannibalism) Satellite Viruses: Require helper virus to replicate Adeno-associated viruses Delta agent (RNA) needs HepB 3. Viroids: short pieces of RNA, no protein coat only been identified in plants, so far Other Noncellular Infectious Agents

26. Most of the time based on symptomology diagnosis

27. Medical: infectious disease Colds Rabies AIDS Ebola Agricultural: plant viruses Ecological: 10 million/ml or 270 million metric tons of organic matter in seawater Research: genetic tools Retroviruses (HIV-1) Treatment of rheumatoid arthritis Adenoviruses (common cold) Cystic fibrosis Poxviruses Canarypox (cancer & rabies treatment) Herpes viruses (cold sores & encephalitis) Infect neurons & CNS Treat tumors in brain Parkinson’s disease Vaccinia virus Vaccines for smallpox & rabies Importance of Viruses