Virology

Question 1

What is a virus?

Answer 1

• collection of genetic information inside a protective protein coat
• obligate intracellular pathogen -> needs host cell machinery to replicate;
  cannot divide/replicate on their own

Question 2

What can viruses be repurposed for?

Answer 2

• Therapeutics (e.g., gene therapy)
• Research tools

Question 3

What are the common vaccines and the way they’re transmitted?

Answer 3

• HIV-1 -> blood, sexual
• hepatitis C-> blood, sexual
• herpes simplex virus-1, 2-> skin contact/sexual

Question 4

What are the rare vaccines and the way they’re transmitted?

Answer 4

• hantavirus -> aerosol
• lassa fever -> aerosol
• west nile -> mosquitoes

Question 5

What are the purposes of the virus structure?

Answer 5

• To protect the viral genome.
• To detect the appropriate host cell for infection.
• To deliver the genome to the correct subcellular site for replication.
• To carry enzymatic activities necessary for initiating viral infection.

Question 6

What are the characteristics of a non-envoloped virus structure?

Answer 6

• a genome surrounded by protein shell (capsid)
• stable to environment
• ex: poliovirus, adenovirus, FMDV

Question 7

What are the characteristics of an envoloped virus structure?

Answer 7

• have a capsid (nucleocapsid) surrounded by a lipid bilayer that has viral proteins protruding from it
• sensitive to environment
• produced by budding
• ex: HIV-1, VZV (chicken pox), influenza

Question 8

What are the 2 types of capsid symmetry?

Answer 8

icosahedral & helical

Question 9

What are the characteristics of icosahedral symmetry?

Answer 9

• not stable in environment
• 20 triangular faces
  12 vertices
• 2, 3 and 5-fold axes
  of rotational symmetry.
  formed from subunits
• “Closed” structure

Question 10

Why are subunits important?

Answer 10

1. Necessity: genome size limits amount of available coding sequence.
2. Self assembly: subunits can come together spontaneously.
3. Fidelity: smaller chances for mutations within small genes.
4. Economy: misfolded proteins cannot be used to form structure (less waste).
5. Complexity: larger number of subunits results in more contacts (stability).

Question 11

What are the characteristics of helical symmetry?

Answer 11

• Rodlike or filamentous structures
• Generally enveloped viruses
• “Open” conformation (adjustable size)

Question 12

What was the criteria used for viruses?

Answer 12

• structure
• type of genome: segmented vs non-segmented
• disease
• host
• containment level
• range: tropism - what cell type does the virus affect?

Question 13

How can you classify a new virus?

Answer 13

1. high thorughout nucleic acid sequencing -> cultured virus; samples from infected individuals
2. PCR -> highly conserved proteins
3. serology -> serum from infected individuals; neutralization
4. electron microscopy -> identify shape, size, symmetry, enveloped vs non-enveloped

Question 14

How can you classify an existing virus?

Answer 14

• genetic material -> RNA or DNA
• capsid symmetry -> icosahedral, helical, complex

Question 15

What is the ICTV classification?

Answer 15

• based on biological classification system
• order: general genome organization
• family: genome organization/gene arrangement
• genus: genome organization/size & sequence homologies
• species: ecological niche
• serotype: antigens
• strain: group in specific geopgraphy

Question 16

What is the genetic content for RNA viruses?

Answer 16

• usually single stranded
• plus -> icosahedral capsids
• minus -> ALL helical capsids; some non-segmented & segented genomes; must be transcribed first!!
• double

Question 17

What is the genetic content for DNA viruses?

Answer 17

• usually double stranded
• exceptions -> parvoviruses & hepadnavirus (HepB)
• linear or circular
• have icosahedral symmetry

Question 18

What are the characteristics of category A CDC select agents?

Answer 18

• easily disseminated or transmitted person-to-person.
• cause high mortality, with potential for major public health impac -> no way of treating
• might cause public panic and social disruption.
• require special action for public health preparedness.

Question 19

What are the characteristics of category B CDC select agents?

Answer 19

• moderately easy to disseminate
• cause moderate morbidity and low mortality
• require specific enhancements of CDC’s diagnostic capacity and enhanced disease surveillance

Question 20

What are the characteristics of category C CDC select agents?

Answer 20

• readily available
• easy to produce and disseminate.
• potential for high morbidity and mortality and major health impact

Question 21

What are the initial stages of infection?

Answer 21

• reservoir
• transmission
• site of infection
• host range
• productive infection

Question 22

What are the host responses to a viral infection?

Answer 22

1. Natural barriers ->ucous membranes, skin
2. Innate immunity -> cells, secreted factors
3. Adaptive immunity -> cellular immunity, humoral immunity

Question 23

What are the 3 patterns of infection & disease?

Answer 23

1. Acute infection followed by viral clearance
2. Acute infection followed by latent infection
3. Acute infection followed by chronic infection

Question 24

What are examples of acute infections followed by viral clearance?

Answer 24

• Colds and respiratory infections -> rhinoviruses, coronaviruses, mild disease (fever, rhinitis)
• Influenza -> 3 major types (A, B, C), moderate disease (fever, rhinitis, bronchiolitis, pneumonia)
• Variola (smallpox) -> 2 forms of disease (major, minor), severe disease (fever, skin lesions, death)

Question 25

What are the characteristics of acute infections followed by viral clearance?

Answer 25

• either localized or disseminated
• ultimately eradicated

Question 26

What problems can arise with an acute infection followed by a viral clearance?

Answer 26

• infection of “non-target” tissue
• not primary tissue of replication
• “dead end” or non-replicating infection
• causes atypical disease
• examples: polio, rubella

Question 27

What are the characteristics of an acute infection followed by latent infection?

Answer 27

• initial infection and apparent clearance
• viral genomes maintained in specific tissues, cell types
• reactivation by physiological responses to external stimuli
• ex: herpes simplex 1

Question 28

What are the characteristics of an acute infection followed by chronic infection?

Answer 28

• initial infection
• partial clearance
• persistent infection and production of virus
• ex: HIV & tumors

Question 29

What are the potential consequences of a chronic infection?

Answer 29

tumors (cancer) & autoimmune diseases

Question 30

How do viruses spread through a population?

Answer 30

• Endemic: continuous transmission within a population
• Epidemic: peaks of disease above baseline or expected rate
• Pandemic: worldwide epidemic