Intro to Virology

Question 1

What is poliomyelitis-poliovirus?

Answer 1

• highly infectious
• neurologic disease
• transmit fecal-oral
• can lead to total paralysis in hrs, die due to immobilization of breathing muscles

Question 2

What was first virus discovered? 3 properties discovered?

Answer 2

tobacco mosaic virus

1. disease transmitted from infected to uninfected leaves but no bacteria or fungus could be cultured
2. organism could pass through filters that retained bacteria
3. organism could reproduce only in association with living plant tissue

Question 3

What are the basic properties of viruses?

Answer 3

• small [filterable] –> average 600 nm in size
• consist of protein, nuclei acid
• obligate parasite –> use host cell machinery for their reporoduction

Question 4

What is structure of virus?

Answer 4

• nucelic acid associated with protein core
• enveloped have lipid envelope with glycoproteins
• non-enveloped just have outer protein coat

Question 5

What is difference in structure enveloped vs non-enveloped virus?

Answer 5

enveloped surrounded by lipid bilayer, envelope comes from host cell membranes
non-enveloped lacks lipid, outside struct is all protein

Question 6

What are the 3 ways in which viruses can be classified?

Answer 6

by nucleic acid: DNA or RNA
by strandedness: double or single
by polarity: + or +/- or -

Question 7

What does it mean for a virus to have + or - polarity?

Answer 7

• means same as complement to mRNA

+ means it is the same as the mRNA that is translated

Question 8

How can viruses be cultured? observed?

Answer 8

• theyre obligate parasites so need to be grown in appropriate living host cell [ex. animal, embryonated chicken egg, cell culture etc]
• cannot be absorbed directly –> look for signs of infection like cytopathic effect, inclusion body formation, hemadsorption

Question 9

What are steps of generic viral replication cycle?

Answer 9

1. viral genom enters host cell
2. viral genome replicated and transcribed
3. viral mRNAs translated and proteins processed
4. particles reassemble inside host then burst or bud to exterior
5. free viral particles in tissue or environment find new host cells to infect

Question 10

What is the eclipse period of viral infection?

Answer 10

no infectious virus found

Question 11

What is the latent period of viral infection?

Answer 11

amount of infectious virus does not exceed the input

Question 12

What is the plateau period of viral infection?

Answer 12

virus titers peak because substrate is dead

Question 13

What is the retrovirus replication cycle?

Answer 13

1. release from previous host cell
2. maturation in tissue
3. attachment to new host cell via receptor
4. penetration of viral genome into host cell
5. uncoating of viral genome
6. genome converted RNA to DNA
7. genome replicated in nucleus and transcribed
8. viral mRNA translated and proteins processed
9. virus reassembles
10. virus buds from host cell membrane and released

Question 14

What is the poxyvirus replication cycle?

Answer 14

• attachment
• encoding
• replication within cytoplasm [it has its own dna and rna polymerase]
• tarsncription
• translation
• reassembly
• release

Question 15

What is path of RNA synthesis for positive-strand RNA viruses? example?

Answer 15

+ genome and mRNA –> anti genome by RNA dependent RNA polymerase –> + genome and mRNA
ex: picornavirus

Question 16

What is path of RNA synthesis for segmented negative-strand RNA virus? examples?

Answer 16

multiple different mRNA segments –> packed to - genome –> copied to + anti-genome –> negative sense viral RNAs

ex. orthomyoxiviridae, bunyarviridae

Question 17

What is path of RNA synthesis for non-segmented negative-strand RNA virus? example?

Answer 17

have single segment that encodes multiple transcriptional units –> converted to neg mRNA –> converted to + antigenome RNA –> converted to neg mRNA

Question 18

What are characteristics of inactivated [killled virus] vaccine?

Answer 18

• elicit antibody response
• may not provide lifelong immunity
• no chance of infecting the vaccinee

Question 19

What are characteristics of subunit vaccines [part of virus is used as immunogen]?

Answer 19

• elicit antibody response
• may not provide lifelong immunity
• no chance of infecting vaccinee

Question 20

What are characteristics of live, attenuated vaccines [viruses that replicated in body]?

Answer 20

• B and T cell responses
• longer lasting immunity, elicit helper T cell responses
• potential for revertants [ex sabin live polio vaccine]

Question 21

Which viruses are part of traditional recommended childhood vaccines?

Answer 21

• hep B
• rotavirs
• inactivated polio
• influenza
• MMR
• varicella
• hepatitis A

Question 22

Which viruses are part of recommended adult vaccines?

Answer 22

• HPV
• MMR
• varicella
• influenza
• hepatitis A
• hep B

Question 23

What type of vaccine is japanese encephalitits?

Answer 23

inactivated virus

Question 24

What type of vaccine is rabies?

Answer 24

inactivated

Question 25

What type of vaccine is smallpox?

Answer 25

live

Question 26

What type of vaccine is yellow fever?

Answer 26

live

Question 27

What do HIV drugs maraviroc and enfuviritide target?

Answer 27

attachment and entry of HIV to cell

Question 28

What do influenza A drugs amandatine and rimantadine target?

Answer 28

uncoating of viral genome

Question 29

What do RT inhibitors [NRTIs, NNRTIs] target?

Answer 29

genome transcription and replication

Question 30

What do influenza virus NA inhibitors target?

Answer 30

viral release from host cell

Question 31

How are viral infections diagnosed?

Answer 31

• clinical presentation
• virus isoaltion and culture followed by detection using HA, HAI, other specific antibody tests
• direct detection of virus antigen in clinical specimen
• seroconversion

Question 32

How are viruses visualized?

Answer 32

indirectly

• -> viral cytopathic effect
• -> HA [hemaglutination] and HAI [ hemaglutination inhibition] tests