1. Viruses Chapter 6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 2 * Many epidemics throughout history * Decline of the Roman Empire? * Europeans bringing their diseases to North America and the decline of the Native Americans * After 100 yrs of Spanish occupation, 90% of Native Americans in Mexico were gone * New England 72,000 in 1600, by 1674 only 8,600 left * Most died from smallpox * Europeans viewed this as proof of their “manifest destiny”

3. 3 * Pasteur first to name: virus means “poison” * 1884 Chamberland devised a filter to trap things smaller than bacteria (filterable) * 1892 Iwanowski discovered that a “filterable” virus caused TMD (plant) * 1898 Frosh & Loffler virus caused foot and mouth disease (animal) * 1901 Walter Reed found yellow fever to be caused by virus (human) * By 1911 – rabies, polio, measles and chicken pox added to list of viral diseases * 1917 Twort discovered bacteriophages * Not photographed until 1930’s

4. 4 * Considered particulates, not cells * Studied in Microbiology because of their small size, unique composition and ability of propagate * Virology: the study of viruses * More than 400 different viruses can inflict humans—very few cures or even fewer antiviral drugs available * Extracellular – outside of host inactive * Intracellular – inside of host active

5. 5 * The ultimate obligate intracellular parasite * Ultramicroscopic size * No independent characteristics of life * Basic structure of protein and nucleic acid * Inactive macromolecules outside host cell * No enzymes for metabolic processes * No machinery for making proteins * They are filterable through standard bacteriological membrane filters * Can form crystal-like masses * NA can be DS DNA, SS DNA, DS RNA or SS RNA * Specific to a certain host cell

6. * Since they are not considered living—don’t follow normal classification schemes * No taxa above “Family” (no kingdom, phylum, etc) * 19 ”Families” of animal viruses * 6 DNA * 13 RNA

7. 7 * Family name ends in -viridae, Herpesviridae * Genus name ends in -virus, Simplexvirus * Herpes simplex virus I (HSV-I) * Disease – Herpes, cold sore * Family – Herpesviridae * Genus – Varicellovirus * Common name – chickenpox virus * Disease - chickenpox

8. 8

9. 9 * All viruses have a capsid- * protein coat that enclose & protect the nucleic acid * Each capsid is constructed from identical subunits called capsomers made of protein * 2 main shapes: * helical * Icosahedral * Nucleocapsid: the capsid and nucleic acid together * Naked virus: just nucleocapsid * Enveloped: additional external covering d erived from host’s cell membrane, nuclear membrane or ER * Spikes: proteins bound to a carbohydrate

10. 10 Helical Capsid

11. * 20-sided with 12 corners * Vary in the number of capsomers * Each capsomer may be made of 1 or several proteins * Some are enveloped 11

12. Complex Capsid Fig 6.9a,c

13. * adsorption – binding of virus to specific molecule on host cell * penetration –genome enters host cell * replication – viral components produced * assembly - viral components assembled * maturation – completion of viral formation * release – viruses leave cell to infect other cells

14. 14 Fig 6.11

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16. 16

17. 17 * Not all bacteriophages lyse cells * Temperate phages insert their viral DNA into the host chromosome & viral replication stops at there until some later time. * Lysogeny- bacterial chromosome carries phage DNA

18. 18 1. Animal virus replication is more complex than phage replication because host cells are more complex. 2. Animal viruses cannot inject their DNA- has to be brought through cell membrane 3. Lysogeny for phage, latency for animal viruses

19. 19 1. adsorption 2. penetration 3. uncoating of genome 4. duplication/synthesis 5. assembly 6. release

20. 20

21. 21 Penetration

22. 22 Release by budding

23. 23 1. Cannot be grown on regular media 2. live animals 3. bird embryos – chicken, duck; intact, self-supporting unit, sterile, self-nourished 4. cell culture

24. 24 * Plaque: clear areas where virus- infected cells have been destroyed * Eclipse Phase: can’t see viral action in the cell (penetration until new viruses formed) * Burst Time: from adsorption to releasing * Burst Size: amount of viruses released * retrovirus: reverse transcription

25. 25 * More difficult than other agents * Consider overall clinical picture * Take appropriate sample * Infect cell culture- look for characteristic cytopathic effects * Screen for parts of the virus * Screen for immune response to virus (antibodies)

26. 26 1. Changes in size & shape 2. Cytoplasmic inclusion bodies 3. Nuclear inclusion bodies 4. Fuse to form multinucleated cells 5. Lysis 6. Alter DNA 7. Transform into cancerous cells

27. * Epstein-Barr (EBV): * Burkitt’s Lymphoma * nasopharyngeal carcinoma * Hepatitis B: liver cancer * HPV: cervical cancer * HIV: Kaposi’s sarcoma * HTLV (Human T-cell Lymphotropic)I: Adult T-cell leukemia * HTLVII: Hairy cell leukemia

28. 28 1. prions - misfolded proteins, contain no nucleic acid * cause spongiform encephalopathies – holes in the brain * common in animals * scrapie in sheep & goats * bovine spongiform encephalopathies (BSE), aka mad cow disease * humans – Creutzfeldt-Jakob Disease 2. viroids - short pieces of RNA, no protein coat * only been identified in plants, so far

29. 29 * Live or killed virus will be used * recommended Infant vaccines (Page 476) * MMR * polio (Salk - killed injected) (Sabin - live oral) * chicken pox * Hepatitis B * Hepatitis A * influenza * DTP * Meningococcal

30. 30 * Smallpox is the only disease to be completely eradicated, last case in 1977 * 1980 WHO recommended destroying stocks of the virus - has not been done yet * doesn’t change shape * vaccine * whole world cooperated