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Chapter 13-Viruses

Chapter 13-Viruses. General Characteristics of all viruses. Contain a single type of nucleic acid Contain a protein coat Obligate intracellular parasites Are viruses the only obligate intracellular parasites?. History began with the Tobacco Mosaic Virus (TMV).

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Chapter 13-Viruses

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  1. Chapter 13-Viruses

  2. General Characteristics of all viruses • Contain a single type of nucleic acid • Contain a protein coat • Obligate intracellular parasites • Are viruses the only obligate intracellular parasites?

  3. History began with the Tobacco Mosaic Virus (TMV) • 1886 Aldolf Mayer showed that a virus was transmissable between plants • 1892 Iwanowski tried to isolate it by filtering with porcelain filter

  4. Sizes of viruses

  5. Polyhedral virus • Capsid coat made of capsomeres • Nucleic acid inside

  6. Helical virus with an envelope • The shape is a long rod • Rabies and Ebola are helical viruses • Influenzae virus is helical with an envelope

  7. Bacteriophage: Complex virus

  8. Bacterial viruses • Known as bacteriophages or phages • Two different life cycles • Lytic cycle-results in lysis of the cell • Lysogenic cycle-may result in lysis of the cell or the virus becomes a permanent part of the chromosome by integrating

  9. Lytic Cycle

  10. Lytic Cycle

  11. Growth curve of bacteriophage

  12. Lysogenic Cycle

  13. How can you study bacteriophages? • Plaque assay -pour agar with bacteria and phage on top of an agar plate -“plaque” develops where virus infected bacterial cell -each plaque is counted as one virus

  14. How do animal viruses differ from bacterial viruses? • Attachment • Replication of nucleic acid • Penetration • Uncoating

  15. DNA Animal Viruses • Adenoviridae • dsDNA, non-enveloped • First isolated in the adenoids • Cause upper respiratory infections

  16. DNA Animal Viruses • Poxviridae • dsDNA, enveloped • Cause small pox (variola)

  17. DNA Animal Viruses • Poxviridae • dsDNA, enveloped • small pox virus (variola)

  18. DNA Animal Viruses • Herpesviridae (dsDNA, enveloped virus) -simplex 1(cold sores) -simplex 2 (genital herpes) -chicken pox, shingles -epstein barr

  19. Herpes simplex-1 • HHV-1 causes fever blisters, HHV-2 genital herpes • Symptoms: fluid filled skin lesions • Treatment: Acyclovir

  20. Varicella (chickenpox) and Herpes Zoster (Shingles) • HHV-3 causes chicken pox and latent activation known as shingles • Acquired by respiratory route, 2 weeks later see vesicles on skin • Vaccine established in 1995 for chickenpox

  21. Epstein Barr • Causes infectious mononucleosis • Acquire by saliva, incubation period is 4-7 weeks • Identify by -lobed lymphocytes -heterophile antibodies -fluorescent antibody tests

  22. Hepadnaviridae • dsDNA, enveloped • Hepatitis B -passes through intermediate stage (RNA) -three particles in blood Dane filamentous sphericle -exposure through blood/body fluids

  23. Hepatitis B • Incubation period is ~12 weeks • 10% of cases become chronic, mortality rate is less than 1% • About 40% of the chronic cases die of liver cirrhosis

  24. RNA animal viruses • Is there an enzyme in animal cells to replicate RNA? • What does RNA polymerase do?

  25. RNA animal viruses • (+) single stranded RNA viruses • RNA serves as mRNA • (-) single stranded RNA viruses • RNA does not code for proteins

  26. Picornaviridae (+) ssRNA • Poliovirus • Virus ingested then travels throughout the body • In some cases it impairs the upper motor neurons, less than 1% of all cases • Vaccines • Salk vaccine (IPV) • Enhanced-inactivated polio (E-IPV) • Sabin vaccine

  27. Cases of Poliomyelitis in US

  28. Picornaviridae (+) ssRNA • Rhinovirus -causes the common cold -100 or more serological types -virus grows best in the nose and conjunctiva

  29. Picornaviridae (+) ssRNA • Enterovirus responsible for 90% of viral gastroenteritis • Rotavirus • Most common cause of viral gastroenteritis • Norwalk-like virus • Responsible for local epidemics

  30. Rotavirus • Note the shape which gave it the name rota=wheel

  31. Picornaviridae (+) ssRNA • Hepatitis A -obtain through fecal-oral route, enters GI tract and multiplies -incubation period is ~4 weeks -symptoms include: anorexia, malaise, nausea, diarrhea, abdominal discomfort, fever, and chills lasting 2-21 days

  32. Flaviviridae (+) ssRNA, enveloped • Hepatitis C virus • Obtain from blood/body fluids • Incubation period averages 6 weeks • Hard to screen blood for the virus • 85% of all cases become chronic

  33. Rhabdoviridae (-)ssRNA, enveloped • Rabies virus -enters the skin and multiplies in skeletal muscle and connective tissue -virus travels along nerves to the CNS causing encephalitis

  34. Pathology of rabies

  35. Orthomyxoviridae-multiple strands of (-)RNA • Influenza virus • Consists of 8 segments of RNA • Envelope has H spikes (hemagglutinin) and N spikes (neuraminidase) • Incubation is 1-3 days • Symptoms include: chills, fever, headache, muscle aches, may lead to cold-like symptoms

  36. Influenza virus

  37. Retroviruses: convert RNA to DNA • HIV, Hepatitis B

  38. Retroviridae-multiple strands of (-)RNA • HIV -infects Helper T cells -requires the enzyme reverse transcriptase -integrates as a provirus -is released by budding, or lyses the cell

  39. Proteinaceous infectious particles: PRIONS • 1982 Stanley Prusiner proposed that there were infectious proteins • Caused the disease “scrapie” in sheep • Caused the “mad-cow”disease in 1987 • Human forms suggest a genetic component

  40. Prions: How do they replicate?

  41. Can viruses cause cancer? • Michael Bishop and Harold Varmus received the 1989 Nobel Prize for cancer-causing genes carried by a virus from animal cells • Oncogenes:genes that can be transformed to cause cancer • 10% of cancers have been found to be due to oncogenic viruses

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