Ch 13

1. Ch 13 Viruses and Prions

2. Student Learning Outcomes Differentiate a virus from a bacterium. Explain the difference between enveloped and nonenveloped viruses. Define viral species. Describe how bacteriophages and animal viruses are cultured. Compare and contrast the lytic and lysogenic cycles of bacteriophages. Define oncogene and transformed cell. Discuss the relationship between viruses and cancer. Explain latent viral infections and give an example. Discuss how a proteins can be infectious.

3. Foundations of Virology Non-living agents that infect all life forms (phages vs. animal viruses) Viral cultivation differs from bacterial cultivation  1,500 known viruses (estimates:  400,000 exist) Advent of EM allowed for visualization of viruses

4. General Characteristics of Viruses • Obligatory intracellular parasites • Filterable • Virus = Latin for poison • Contain DNA or RNA • Contain a protein coat = capsidmade up of capsomeres. Various shapes • Some are enclosed by an envelope (naked vs. enveloped) • Some viruses have spikes (COH/protein) • Most viruses are tissue specific • Host range is determined by specific host attachment sites and cellular factors

5. Host Range and Specificity Usually narrow host range – due to? Tissue tropism Phage Therapy Oncolytic viruses

6. Virus Shapes and Sizes Fig 13.1

7. Virion Structure • Nucleic acid • DNA or RNA • Capsid • Capsomeres • Envelope • Spikes Fig 13.2

8. Morphology of an enveloped helical virus Example of a enveloped polyhedral virus: Hepes simplex

9. Polyhedral Smallpox virus Complex symmetry Compare to Figs 13.3 - 13.5

10. Taxonomy of Viruses • No evidence for common viral ancestor. • Classification based on genomics and structure. • Familynames end in –viridae • Genus and species names end in -virus. • Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species. • Subspecies are designated by a number.

11. Family: Retroviridae Genus: Lentivirus Species and subspecies: Human immunodeficiency virus 1 and 2 (HIV-1, HIV-2) Examples of Naming Viruses Briefly review Table 13.2 • Family: Herpesviridae • Genus: Varicellovirus • Species and subspecies: Human herpes virus 3 (HHV-3 • Family: Picornaviridae • Genus: Hepatovirus • Species and subspecies: Hepatitis A virus

12. Isolation, Cultivation, and Identification of Viruses Fig 13.6 • Viruses must be grown in living cells Bacteriophages form plaques on a lawn of bacteria Animal viruses may be grown in cell culture, embryonated eggs (Fig 13.7), or living animals Fig 13.8

13. Virus Identification • Serological tests • Detect antibodies against viruses in a patient • Use antibodies to identify viruses (more after Immunology chapter discussion) • Nucleic acids methods • RFLPs • PCR

14. Viral Multiplication • Obligate intracellular parasites using host cell machinery • Very limited number of genes encode proteins for • Capsid formation • Viral nucleic acid replication • Movement of virus into and out of cell • Kill or live in harmony within the host cell – Outside the cell, viruses are inert

15. 2 Mechanisms of Bacteriophage Multiplication • Lytic cycle(by lytic or virulent phage) Phage multiplies, eventually causing lysis and death of host cell • Lysogenic cycle(by lysogenic or temperate phage) Phage DNA incorporated in host DNA  Prophage. No host cell lysis, cell lives.3 results of lysogeny: • Lysogenic cell immune to reinfection by same phage • Phage conversion • Possibility for specialized transduction Mastering: Viral Multiplication

16. T-Even Bacteriophage:The Lytic Cycle • Attachmentto cell surface receptors (chance encounter – no active movement) • Penetration– only genome enters • Biosynthesis–Production of phage DNA and proteins • Maturation– assembly to form intact phage • Releasedue to phage induced lysozyme production See Fig 13.11

17. Lytic Cycle of a T-Even Bacteriophage 1 2 3 Fig 13.11

18. Some animal viruses exit the host cells via budding HSV envelopment and release Fig. 13.20

19. Lytic and Lysogenic Cycles ( Phage) Fig 13.12

20. Multiplication of Animal DNA Viruses Foundation Fig 13.15

21. Multiplication of a Retrovirus Fig 13.19

22. Cancer - Oncology Cancer  uncontrolled mitotic divisions Benign vs. malignant tumors Carcinoma vs. Sarcoma Adenocarcinoma 3 important characteristics of cancer cells: • Rapid cell division • Loss of anchoring junctions and contact inhibition  metastasis • Dedifferentiation of cells

23. Viruses and Cancer • The genetic material of oncogenic viruses becomes integrated into the host cell’s DNA (provirus). • Conversion of proto-oncogenes to oncogenes • Activated oncogenes transform normal cells into cancerous cells • Transformed cells have increased growth, loss of contact inhibition, tumor-specific transplantantigens(TSTAs) • Oncogenic Viruses are responsible for 10 % of human cancers

24. OncogenicDNA Viruses andRNA Viruses • HPV  _________cancer • Epstein-Barr virus (EBV) Burkitt’s lymphoma • HHV8  Kaposi’s sarcoma • HBV  _________cancer • Hepatitis C virus (HCV)  liver cancer • human T-cell leukemia virus (HTLV-1)

25. Latent and Persistent Viral Infections Latent:Virus remains in asymptomatic host cell for long periods Persistent:Disease processes occurs over a long period; generally is fatal Fig 13.21

26. Prions = • Inherited and transmissible by ingestion, transplant, and surgical instruments • Cause spongiform encephalopathiesHuman and 9 animal diseases, such as: • Scrapie, • Mad cow disease • CJD, • Kuru • PrPC: Normal cellular prion protein, on cell surface. Involved in cell death regulation. • PrPSc: Scrapie protein; accumulates in brain cells, forming plaques. Review Fig 13.22

27. Spongiform Encephalopaties Caused by altered protein: • Mutation in normal PrPcgene (sporadic CJD), or • contact with the abnormal PrPSc protein (Kuru) Mastering: Prions The End