Basic Virology

Question 1

Viral structure

Answer 1

• Naked virus w/ icosahedral capsule: nucleic acid + capsid
• Enveloped virus w/ icosahedral capsule: nucleic acid + capsid + lipid bilayer + surface protein
• Enveloped virus w/ helical capsid: helical capsid w/ nucleic acid inside, lipid bilayer, surface protein

Question 2

Viral genetics

Answer 2

• Recombination
• Reassortment
• Complementation
• Phenotypic mixing

Question 3

Recombination

Answer 3

Exchange of genes btwn 2 chromosomes by crossing over w/ regions of base homology

Question 4

Reassortment

Answer 4

Cell infected with 2 Viruses w/ segmented genomes exchange segments
- Cause of worldwide flu epidemics

Question 5

Complementation

Answer 5

1 of 2 viruses that infect the cell has mutation –> nonfxnal protein
- The nonmutated virus “complements” the mutated one by making fxnal protein that serves both viruses

Question 6

Phenotypic mixing

Answer 6

Simultaneous infection of cell w/ 2 viruses - genome of A coated w/ surface proteins of B (hybrid)

• Then coat of B determines infectivity of hybrid virus
• But progeny have type A coat, encoded by type A genetic material

Question 7

Viral vaccines

Answer 7

• Life attenuated
• Killed
• Recombinant

Question 8

Live attenuated vaccines

Answer 8

Induce humoral/cell-mediated immunity; revert to virulence rarely

• No booster needed; dont give to immunocompromised!
• Smallpox, yellow fever, chickenpox (VZV), Sabin polio, MMR, Influenza (intranasal)

Question 9

Killed vaccines

Answer 9

Induce only humoral activity; stable (no virulence)

• Rabies, influenza (injected), salk polio, HAV vaccines
• SalK = Killed*

Question 10

Recombinant vaccines

Answer 10

Induce only humoral activity; stable (no virulence)

- HBV, HPV (6,11,16,18)

Question 11

DNA viral genomes

Answer 11

• All DNA viruses except parvo are dsDNA
• “Part-of-a-virus (parvo) is ssDNA; parvus = small*
• All are linear except papilloma-, polyoma-, hepadnaviruses (circular)

Question 12

RNA viral genomes

Answer 12

• All RNA viruses except reoviridae are ssDNA
• Positive-stranded RNA viruses: retrovirus, togavirus, flavivirus, coronavirus, hepevirus, calicivirus, picornovirus

“went to a retro toga party, drank flavored Corona and ate hippy california pickles”

Question 13

Infectivity of naked viral genomes

Answer 13

Infectious: dsDNA (except poxvirus/HBV) and +ssDNA viruses

Not infectious: -ssDNA and dsRNA, poxvirus/HBV
Need polymerase in complete virion

Question 14

Viral replication

Answer 14

DNA - replicate in nucleus (except poxvirus)

RNA - replicate in cytoplasm (except influenza/retroviruses)

Question 15

Viral envelopes

Answer 15

Naked viruses (no envelope):

• Papillomavirus, Adenovirus, Parvovirus, Polyomavirus, Calicivirus, Picornavirus, Reovirus, Hepevirus
• Give PAPP smears and CPR to naked HEPpy (hippy)*
• PAPP = DNA viruses
• CPR + hepevirus = RNA viruses

Question 16

DNA virus characteristics

Answer 16

HHAPPPPy viruses
- Hepadna, Herpes, Adeno, Pox, Parvo, Papilloma, Polyoma

Double stranded (except parvo)

Linear (except papilloma, polyoma, hepadna)

Icosahedral (except pox = complex)

Replicate in nucleus (except pox; carries own DNA-dep RNA polym)

Question 17

Genetic shift/antigenic shifts

Answer 17

Cause pandemics –> reassortment of viral genome

• Segments undergo high-freq recombination
• i.e. when human flu A virus recombines with swine flu A virus

Question 18

Genetic drift

Answer 18

Cause epidemics

- Minor (antigenic drift) changes based on random mutation