Chapter 13: Reoviruses and other dsRNA

Question 1

Reoviridae

Answer 1

Respiratory
Enteric
Orphan (“no” disease association)

Question 2

Reoviridae Virion

Answer 2

• Spherical (icosahedral symmetry)
• 60-80 nm in diameter
• Genome: dsRNA, 10~20 segments, 18~32 kbp
• Usually naked

Question 3

Rotavirus

Answer 3

“wheel” in Latin

Question 4

Rotavirus Virion

Answer 4

Spherical, wheel like
Icosahedral symmetry
75 nm in diameter
Triple layer particle

Question 5

Triple Layered Particle

Answer 5

Inner layer made of VP2
Middle layer made of VP6, contain “spokes” of the wheel
Outer layer made of VP7 (glycoprotein)

Question 6

VP1

Answer 6

RNA polymerase

Question 7

VP3

Answer 7

capping enzyme

Question 8

Rotavirus Genome

Answer 8

11 dsRNA segments, 22 kbp
(+) strands are all capped
No poly A
12 gene products

Question 9

Each segment in Rotavirus genome

Answer 9

Associated with VP1 and VP3
Has unique sequence for assembly
Has 1 ORF except that RNA 11 has 2 ORFs in different reading frames

Question 10

Rotavirus Attachment

Answer 10

Many details unclear
Cleavage of Spike protein VP4
Spike proteins and capsid glycoprotein interact with cell surface proteins

Question 11

Cleavage of VP4

Answer 11

Into VP8* and VP5* by trypsin

Question 12

Rotavirus Entry

Answer 12

Direct penetration (mediate by hydrophobic VP5*)
or endocytosis

Question 13

Rotavirus Entry Events

Answer 13

Remove outer layer
Early transcription inside double-layered particle
Translation and modification
NSP2 and NSP5 assemble viroplasm
VP1, VP3 bind to (+) RNA, then to VP2 -> form core
(-) RNA synthesis inside core
VP6 attach core -> double layer particle

Question 14

Viroplasm

Answer 14

viral protein accumulating region for viral replication/assembly

Question 15

Rotavirus Late Events

Answer 15

Late transcription inside double-layered particles -> late mRNA not capped
Cell translation machinery changes
NSP4 and VP7 synthesized in rough ER
Virus controls the quantity of each of 12 viral proteins produced
NSP4 binds VP4 and double-layered particles
The complex buds through ER into a vesicle
VP7 cleaved from vesicle membrane -> build outer layer
VP4- form spikes
Virions released via cell lysis

Question 16

Rotavirus disease

Answer 16

leading cause of severe diarrhea among young children

Question 17

Transmission, Infection, Disease

Answer 17

fecal-oral route
enterocytes at the tips of villi in small intestine
Gastroenteritis

Question 18

Rotavirus Pathogenesis

Answer 18

destroy enterocytes of villi -> malabsorption of water solutes from gut-> diarrhea

Question 19

Rotavirus Syptoms

Answer 19

vomiting, profuse watery diarrhea, fever

Question 20

Other Rotavirus disease facts

Answer 20

Incubation 2 days
Infectious does 10-100 virions
Death due to dehydration
Treatment is rehydration
Self-limiting

Question 21

Other dsRNA viruses

Answer 21

most naked and have icosahedral symmetry

dsRNA is a potent inducer of cell defense mechanisms

Question 22

Cell defense mechanisms

Answer 22

Apoptosis
Interferon production
RNA silencing