Virus Basics

Question 1

Differences between bacteria and virus:
Alive?
Size?
Genome?
Reproduction?
Pathogenesis?
Treatment?

Answer 1

Bacteria are:
Alive
Light microscope visible
Bigger genome (DNA)
Binary fission
Trigger inflammation/produce toxins
Antibiotics (many)

Viruses:
Not alive
EM visible
Small RNA or DNA genome
Self-assembly in host cell
Replication in host cell causes lysis or cell death
Antivirals (few)

Question 2

What percent of the human genome is viral?

Answer 2

8%

Question 3

Components of a protypical virus (and variations of each component)

Answer 3

-Genome (RNA+/- or DNA; ss or ds; circular or linear; continous or segmented)

-Capsid (structural proteins- icosahedral, helical, cone of complex)
(nucleocapsid= genome +capsid)
-Envelope

Question 4

Differences in stability between enveloped and non-enveloped viruses

Answer 4

Enveloped are less stable in the environment

Question 5

4 different kinds of viral morphology

and which part of the virus is responsible for its morphology?

Answer 5

Icosohedral (20-sided)
Helical
Cone shaped
Complex (no symmetry)

The capsid proteins are responsible for morphology

Question 6

Stages of viral replication

Answer 6

1) attachment (need receptors on host cell)
2) penetration (via fusion or endocytosis)
3) uncoating (viral genetic material released)
4) replication (with host machinery)
5) assembly (capsomeres self assembled)
6) release (lysis (non-enveloped) or budding (enveloped)

Question 7

Most common mechanisms of transmission

• Vertical
• Horizontal

Answer 7

Vertical

• transplacental
• perinatal
• breast milk

Horizontal

• repiratory (droplets or aerosols)
• fecal-oral (contaminated food, water, fomites)
• contact (exchange of fluids)
• blood (injection drugs, sexual)
• animal vectors
• insect vectors
• Iatrogenic (contaminated instruments)
• Bioterrorism

Question 8

The host response to viruses (general)

Answer 8

Innate immunity

• barriers
• macrophages and NK cells

Adaptive immunity

• neutralizing antibodies
• T-cells kill virally infected cells

Question 9

Chronic vs. Latent infection

Answer 9

Chronic: steady-state infection where viral replication is equalled by immune response

Latent: viral genome is passed to daughter cells, but no viral proteins are made.

Question 10

RNA viruses reproduce (faster/slower?) than DNA viruses

Answer 10

Faster

Question 11

Rapidly replicating viruses need to evade….
Intermediate replicating viruses need to evade…
Slow replicating viruses need to evade….

Answer 11

Rapid: only innate immune functions
Intermediate: innate and adaptive (e.g. mutability)
Slow: elaborate mechanisms to evade innate and adpative

Question 12

Being a big virus is better for _____ but worse for _____

Answer 12

immune evasion

speed of reproduction