Viruses

Question 1

Obligate intracellular pathogen

Answer 1

Uses host cell machinery to replicate, cannot divide or replicate on their own, and do not metabolize small molecules for energy

Question 2

How are viruses classified?

Answer 2

Virion size and structure
Type of nucleic acid
Replication strategy
Virion stability and antigenicity

Question 3

Non-enveloped (naked capsid)

Answer 3

• Composed of proteins
• Environmentally stable
• Released from cell by lysis
• Consequences: spread easily, dry out and retain infectivity, survive gut, resistant to detergents and poor sewage, antibody may be sufficient for immunosuppression

Question 4

Enveloped

Answer 4

• Composed of membrane, lipids, proteins, glycoproteins
• Environmentally labile
• Is released by budding and cell lysis
• Consequences: must stay wet, cannot survive gut, spreads in lg droplets, secretions, does not need to kill cell to spread, may need protection and control, elicits hypersensitivity and inflammation to cause immunopathogenesis

Question 5

General virus life cycle

Answer 5

1. ) Initial binding to cell receptors
2. ) Attachment to cell by general or specific receptors
3. ) Entry into cell - endocytosis (nonenveloped) or direct fusion (enveloped)
4. ) Uncoating of genome from capsid
5. ) Gene expression by transcription or replication
6. ) Protein translation by host ribosomes
7. ) Genome replication by viral or host polymerase
8. ) Particle assembly forms new virus
9. ) Budding/egress from cell

Question 6

Where does RNA replicate? DNA?

Answer 6

Cytoplasm; nucleus

Question 7

Modes of transmission

Answer 7

Horizontal - aerosol, fecal-oral, blood-borne, vector-borne

Vertical - mother»placenta or breast milk»child

Question 8

Cell tropism

Answer 8

Which cells are infected by the virus

Question 9

Host range

Answer 9

Which species (or cells from the species) can be infected by the virus

Question 10

Effects of viral infection

Answer 10

Cell destruction (lysis, cell/viral proteins, CTL triggered apoptosis)
Cell transformation
Immunosuppression
Latent/persistent infection
Immunopathology

Question 11

Host response to viral infection

Answer 11

Natural barriers (skin and mucous)
Innate immunity (interferons and cytokines, cells)
Adaptive immunity (T and B)
Seroconversion (antibody against viral proteins can be detected in serum)

Question 12

Virus evasion of immune response

Answer 12

Active (inhibition) - infect and destroy immune cells, block MHC presentation of viral antigens, prevent lymphocyte prolif
Passive (avoidance) - antigenic variation, infection of immune privileged sites, down regulation of viral gene expression