1. Viruses
Chapter 13

2. Viruses, Viroids and Prions
Viroids – infectious pieces of naked RNA
Proins – infectious proteins
Viruses, Viroids and Prions
Ch. 13

3. Study of Viruses - Virology
5 Kingdoms
1. Plantae
2. Animalia
3. Fungi
4. Protista
5. Monera

4. 5 Characteristics of Life
1. Cells
2. Grow and maintain their structure by taking up chemicals and energy from the environment
3. Respond to their external environment
4. Reproduce and pass on their organization to their offspring
5. Evolve and Adapt to their environment

5. Viruses are: 1. Acellular 2. Obligate intracellular parasites
3. No ATP generating system
4. No Ribosomes or means of Protein Synthesis

6. Typical Virus 2 Parts 1. Nucleic Acid 2. Capsid (Coat Protein)
DNA or RNA (But never both)
2. Capsid (Coat Protein)
Some Viruses:
A. Envelope
B. Enzymes

7. Host range Spectrum of host cells that a virus can infect
Some viruses only infect:
plants
invertebrates
protists
fungi
bacteria (Bacteriophages)

8. Host range Most viruses have a narrow host range
Polio virus nerve cells
Adenovirus - cells in upper Respiratory Tract

9. Host range is determined by Viruses ability to interact with its host cell
Binding Sites match Receptor Sites
Binding Sites - on viral capsid or envelope
Receptor Sites - on host cell membrane

10. Viral Size
20 nm to 1,000 nm
.02 u to 1 u

11. Viral Structure 1. Nucleic Acid 2. Capsid (Coat Protein) Nucleic Acid
DNA or RNA (But never both)
ssDNA
ds DNA
ss RNA
ds RNA

12. Viral Structure Capsid (Coat Protein) Envelope
protects viral genome from host endonucleases
capsomeres
Binding Sites
Envelope
derived from the host cell

13. Viral Morphology
1. Helical

14. Viral Morphology
2. Polyhedral
icosahedral

15. Viral Morphology 3. Enveloped A. Enveloped Helical
B. Enveloped Polyhedral

16. Viral Morphology
4. Complex

17. Viral Classification 1. Nucleic Acid 2. Morphology
3. Strategy for replication

18. Growing Viruses 1. Bacteriophages Lawn of Bacteria on a Spread Plate
Add Bacteriophages
Infection will result in “Plaques”
Clear zones on plate

19. Growing Viruses Animal Viruses A. Living Animals
mice, rabbits, guinea pigs
B. Chicken Embryos (Eggs)
used to be most common method to grow viruses
Still used to produce many vaccines (Flu Vaccine)
C. Cell Cultures
Most common method to grow viruses today

20. Cell Cultures 1. Primary Cell Lines B. Diploid Cell Lines
die out after a few generations
B. Diploid Cell Lines
derived from human embryos
maintained for up to 100 generations
C. Continuous Cell Lines
Transformed Cells (Cancerous Cells)
may be maintained indefinitly
HeLa Cells
Henrietta Lax (Cervical Cancer)

21. Viroids and Prions Viroids Naked RNA (no capsid)
300 – 400 nucleotides long
Closed, folded, 3-dimensional shape (protect against endonucleases ?)
Plant pathogens
Base sequence similar to introns

22. Prions Proteinaceous infectious particle 1982 Diseases Scrapie (sheep)
Creutzfeldt-Jacob disease (CJD)
Kuru (Tribes in New Guinea)
Bovine Spongiform Encephalopathy (BSE)
Mad Cow Disease
CJD – Neurological disorder
Kuru – Transmitted by contact with brain and tissue of dead victims

23. Viral Replication
Bacteriophage
1. Lytic Cycle
2. Lysogenic Cycle

24. Lytic Cycle
1. Attachment- binding sites must match receptor sites on host cell
2. Penetration - viral DNA is injected into bacterial cell
3. Biosynthesis
Genome replication
Transcription
Translation
Virus uses Host Cells enzymes and machinery

25. Lytic Cycle 4. Assembly (Maturation) 5. Release
viral particles are assembled
5. Release
Lysis

26. Lysogenic Cycle 1. Attachment 2. Penetration 3. Integration
Viral Genome is integrated into Host Cell Genome
Virus is “Latent”
Prophage

27. Lysogenic Cycle 4. Biosynthesis - Viral Genome is Turned On
Genome replication
Transcription
Translation
5. Assembly
6. Release
Lysis

28. Lysogenic Convergence
1. Corynebacterium diphtheriae
2. Streptococcus pyogenes
Scarlet Fever
3. Clostridium botulinum

29. Animal Virus Replication (non-enveloped virus)
1. Attachment
Binding Sites must match receptor sites on host cell
2. Penetration
Endocytosis (phagocytosis)
3. Uncoating
separation of the Viral Genome from the capsid

30. Animal Virus Replication (non-enveloped virus)
4. Biosynthesis
Genome Replication
Transcription
Translation
5. Assembly
Virus particles are assembled
6. Release
Lysis

31. Enveloped Virus Replication
1. Attachment
2. Penetration
3. Uncoating
4. Biosynthesis
5. Assembly
6. Release
Budding

32. Retro Viruses (1975) Central Dogma of Molecular Genetics
DNA > mRNA > Protein
Central Dogma of Molecular Genetics
Normal Virus
RNA > DNA > mRNA > Protein
Retro Virus

33. Reverse Transcriptase (Retro)

34. Retro Viruses 1. Many Cancer causing viruses 2. HIV
Human Immunodeficiency Virus
AIDS
Acquired Immunodeficiency Syndrome

35. HIV (Human Immunodeficiency Virus)
AIDS
Acquired Immune Deficiency Syndrome
results in failure of the immune system
Death usually results from an Opportunistic Infection
HIV discovered in 1984
By who ?
Luc Montagneir - Pasteur Institute

36. HIV Structure Retro Virus Nucleic acid - RNA (2 strands)
envelope (gp 120 binding sites)
Reverse Transcriptase

37. HIV Infection (Cellular Level)
1. Attachment
HIV gp 120 binding sites must match CD4 receptor sites
CD4 Receptor Sites
1. Macrophages
2. Some cells of CNS
3. T4 Helper Cells (CD4 Cells)

38. HIV Infection 2. Penetration 3. Uncoating
Viral membrane and host cell membrane merge (fusion)
3. Uncoating
Capsid is removed and Viral Genome is exposed

39. HIV Infection 4. Integration
Once Viral Genome is integrated - 2 possibilities:
1. Nothing - Virus is “Latent”
Virus may be latent for days, weeks, months or years
Median latency time = 10 years

40. Latent HIV provirus

41. 2. HIV Genome can be “expressed” or “Turned On”
Once HIV Genome is “turned on” death usually results within 2 years
What causes the HIV Genome to be “turned on”?
Other infections
Stress or shock to the system
Drug abuse
Alcohol abuse
Nutrition
Exercise (Lack of or too much?)
Sunburn ?
(Herpes Simplex 1)

42. Once HIV Genome is “turned on”
5. Biosynthesis
Genome replication
Transcription
Translation
6. Assembly
Virus particles are put together
7. Release
Budding

43. Modes of HIV Transmission
HIV is transmitted by exposure to infected body fluids
4 Body Fluids
1. Blood
2. Semen
3. Vaginal Secretions
4. Breast Milk

44. How are these fluids transferred from one person to another?
1. High Risk Sexual Contact
unprotected vaginal sex
unprotected oral sex
unprotected anal sex
2. Needles
Intravenous Drug Abuse (sharing dirty needles)
accidental needle sticks

45. How are these fluids transferred from one person to another?
3. Blood to Blood Contact
open sores or wounds
Transfusions
Organ Transplants
Artificial Insemination
4. Mother to Child
placenta
as baby passes thru the birth canal
breast milk

46. HIV and the Immune System
1. Cellular Immune System
cells phagocytize microbes
2. Humoral Immune System
antibodies to destroy or inactivate microbes

47. Clinical Stages of an HIV Infection
1. Acute Infection
Initial infection of HIV (exposure to infected body fluids)
Viremia
Fever
Headaches
Weakness
Muscle and joint aches
May last for a couple of weeks
Normal CD4 cell count mm3

48. 2. Asymptomatic Disease CD4 cell count < 1000mm3
Virus is “latent” inside CD4 cells
Median latency period - 10 yrs.
No signs or symptoms of illness (asymptomatic)
HIV Positive - antibodies can be detected in your blood
Seroconversion
6 to 8 weeks

49. 3. Symptomatic Disease CD4 cell count < 600mm3
Viral Genome is “turned on”, Symptoms begin to appear
What causes HIV Genome to be turned on?
Other infections
stress
shock to the system
alcohol
drug abuse
nutrition
exercise ?

50. 3. Symptomatic Disease Symptoms Susceptible to Infections
chronic fatigue
low-grade fever
night sweats
diarrhea
weight loss
Susceptible to Infections
bacterial pneumonia
meningitis
oral and vaginal yeast infections
tuberculosis

51. 4. Advanced Disease (AIDS)
CD4 cell count < 200mm3
Severe Opportunistic Infections
Pneumocysitis carinii pneumonia (PCP) Fungi
Kaposi’s Sarcoma ( Cancer - Skin and Blood vessels)
Toxoplasmosis (Brain) Protozoan
Cryptosporidiosis (G.I. Tract) Protozoan
Other Bacterial, Fungal and Viral Infections

52. HIV Infection and Immune Response (Graph)

53. Enzyme Linked Immunosorbant Assay
Blood Test ELISA
Enzyme Linked Immunosorbant Assay
tests for HIV Antibodies
If ELISA is positive, same sample is tested again
If ELISA is positive again, then a Western Blot Test is done.
Western Blot - test for Viral antigens

54. Treatment for HIV Infection
No Cure
AZT ( Azidothymidine)
Thymine analog
lacks a 3’ OH
Chain Terminator
Inhibits Reverse Transcriptase

55. AIDS Cocktail (Combination Therapy)
AZT
3TC ( 2’-deoxy-3’-thiacytidine)
Protease Inhibitor

56. Vaccine for HIV ? HIV mutates too rapidly
Reverse Transcriptase causes at least 1 mutation each time it is used
1 million variants during Asymptomatic Disease
100 million variants during Advanced Disease (AIDS)