1. Chapter 13-Viruses of Bacteria

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. Parts of a virus

7. Relationship of virus with host cell

8. Shapes of a virus

9. Bacterial viruses Known as bacteriophages or phages Two different life cycles 1.Lytic cycle (virulent)-results in lysis of the cell 2.Lysogenic cycle (temperate)-may result in lysis of the cell or the virus becomes a permanent part of the chromosome by integrating

10. T4 phage replication

11. Lambda Phage

13. Lambda integrates into the chromosome

14. Properties conferred by prophage

15. Some phage are filamentous

16. Replication of filamentous phage

17. M13 is ssDNA…how does it replicate the ssDNA?

18. Chapter 14: Animal Viruses

19. How do animal viruses differ from bacterial viruses? Attachment Replication of nucleic acid Uncoating Exit by budding

20. Entry by membrane fusion

21. Entry by endocytosis

22. Replication of nucleic acid

23. Release by budding

24. Persistant infections Virus is continually present in the body, released by budding Three categories –Latent infections –Chronic infections –Slow infections

25. Latent Infections Persistant infection with symptomless period followed by reactivation of virus and symptoms Herpesviridae –Herpes simplex virus -1 –Herpes simplex virus -2

26. Latent Viral infections

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

28. Herpes Simplex virus-1

29. HSV-1 reactivation

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

31. 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

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

33. Chronic infections Infectious virus present at all times Disease may be present or absent Best example is Hepatitis Type B virus –Carriers produce virus detected in blood, saliva, and semen –Unique replication of dsDNA

34. Chronic Viral infections

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

36. 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

37. Slow Infections Infectious agent increases in amount over a long time during which there are no symptoms Examples are HIV found in the Retroviridae family Retroviruses use reverse transcriptase to replicate ssRNA

38. Retrovirus

39. Viruses and tumors dsDNA viruses are most common to cause viral-induced tumors Cancer is result of integration of viral genes into the host chromosome Transforming genes are called oncogenes Examples: papillomavirus, herpesvirus

40. Viruses associated with cancers

41. Viruses can alter their genome by reassortment

42. 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

43. Influenza virus

44. Ways to study viruses Since viruses grow in living cells….need a live cell to culture them –Cell culture/tissue culture –Embryonated chicken eggs

45. Cell Culture

46. Quantitation of viruses

47. 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

48. Prions Contain no nucleic acid Abnormal protein promotes conformational change to normal protein Results in damage to neurons…transmissable spongiform encephalopahthies

49. Brain with spongiform encephalopathy

50. Infections caused by prions

51. Mechanism of prion replication

52. 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

53. 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

54. 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

55. Pathology of rabies

56. 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