Lecture 32 - Norovirus

Question 1

Why are gastroenteric viruses hard to control?

Answer 1

1) By the time you feel ill or mount an immune response, most acute infections are complete.
2) Virus has spread to another host by the time immune response is mounted

Question 2

Proportion of infective diarrhoeas that are viral

Answer 2

75%

Question 3

First and second most common types of viral illness

Answer 3

1st - upper respiratory

2nd - gastroenteritis

Question 4

Viruses that invade GAT to cause systemic illness
1)
2)

Answer 4

1) Hep A

2) Enterovirus

Question 5

Type of cells in the intestinal epithelial monolayer

Answer 5

Columnar vilious epithelial cells

Question 6

Common site of viral pathogen entry in GIT

Answer 6

M cells

Question 7

Most important immune response to gastroenteric viruses

Answer 7

Primary immune response.

Takes 7-10 days for adaptive to mount, but viral infection often controlled after three days.

Question 8

What is the adaptive immune response important for in gastroenteric viruses?

Answer 8

Final clearance of the virus, memory

Question 9

Viral family of norovirus

Answer 9

Caliciviridae (ssRNA, non-enveloped)

Question 10

Size of norovirus virion

Answer 10

25-35nm

Question 11

Proportion of serious gastroenteritis cases attributable to norovirus

Answer 11

~20%

Question 12

When is norovirus more common?

Answer 12

Winter

Question 13

Norovirus demographic most at risk

Answer 13

Infects adults and children at equal rate

Question 14

Norovirus incubation period

Answer 14

Normal is under 24 hours.

Range is 12-48 hours.

Question 15

Duration of norovirus symptoms

Answer 15

Around 3 days

Question 16

Norovirus symptoms 
1
2
3
4
5
6

Answer 16

1) Nausea
2) Fever
3) Headache
4) Abdominal cramping
5) Vomiting
6) Watery diarrhoea

Question 17

Norovirus epidemiology
1
2
3
4

Answer 17

1) Worldwide distribution
2) ~2 million cases/year in Australia
3) Major cause of foodborne gastro outbreaks
4) Most people are seropositive at four years

Question 18

Norovirus genotype that often causes pandemics

Answer 18

Norovirus GII.4

Question 19

Number of pandemics associated with norovirus GII.4

Answer 19

Six.

Question 20

Proportion of norovirus outbreaks caused by GII.4 genotype

Answer 20

62-80%

Question 21

Number of breakpoints identified in norovirus GII.4 lineage

Answer 21

11

Question 22

Three recombination hotspots in norovirus GII.4 lineage

Answer 22

1) Open reading frame 1/2 overlap
2) Open reading frame 2/3 overlap
3) Within open reading frame 2 (which encodes VP1 viral capsid)

Question 23

Number of capsid proteins in norovirus

Answer 23

Only one - VP1

Question 24

Why is there such a high norovirus mutation rate?

Answer 24

RDRP mistakes.

Recombination

Question 25

NIAID class of norovirus

Answer 25

Class II bioterrorism agent

Question 26

How long after cessation of symptoms can norovirus be secreted?

Answer 26

4-6 weeks

Question 27

Infective dose of norovirus

Answer 27

10-100 pfu

Question 28

Type of water treatment that norovirus can survive

Answer 28

Chlorination at normal levels (EG: in a swimming pool)

Question 29

Primary norovirus transmission
1
2

Answer 29

1) Contamination of foods at raw stage (EG: infect shellfish that filter feed infected water)
2) Application of contaminated water to crops

Question 30

Secondary norovirus transmission

Answer 30

Infected workers contaminate food

Question 31

Name of Perth cruise ship with repeated norovirus outbreaks

Answer 31

Sea Princess

Question 32

Norovirus detection
1)
2)
3)

Answer 32

1) Specimen detection (EM) on stool, vomitus (can’t detect on food)
2) RT-PCR
3) Serology

Question 33

Is there a human tissue culture for norovirus?

Answer 33

No

Question 34

Type of beverage that worsens norovirus symptoms

Answer 34

Sugary

Question 35

Norovirus vaccine

Answer 35

Doesn’t exist

Question 36

Why is little understood of norovirus replication and pathology?

Answer 36

No human tissue culture that can grow norovirus.

Can only be grown in murine models, which don’t display the same symptoms as in humans

Question 37

Initial observation that led to development of murine norovirus model

Answer 37

RAG-/-, IFNabR-/- or IFNgR-/- survived murine norovirus infection

IFNabgR-/- or STAT1-/- succumbed to norovirus infection

Question 38

Which cells does murine norovirus replicate in?

Answer 38

Macrophages, monocytes, DCs

Question 39

Size of norovirus genome

Answer 39

7.5kb

Question 40

Genes in norovirus ORF1

Answer 40

Non-structural genes

Key enzymes NS6 (protease) and NS7 (RDRP)

Question 41

How are norovirus capsid VP1 and small basic protein VP2 transcribed?

Answer 41

Subgenomic RNA

Question 42

Contents of norovirus ORF2

Answer 42

VP1 capsid

Question 43

Contents of norovirus ORF3

Answer 43

VP2 small basic protein

Question 44

Contents of norovirus ORF4

Answer 44

VF1 virulence factor

Question 45

How are norovirus nonstructural proteins initially translated?

Answer 45

As a polyprotein

Question 46

How are norovirus non-structural proteins expressed?

Answer 46

As a polyprotein, which is cleaved by NS6 protease

Question 47

Effects of norovirus on host cell architecture

Answer 47

Forms membranous structures in cytoplasm.

Murine norovirus replicates on these structures

Question 48

Marker for norovirus replication

Answer 48

dsRNA

Question 49

Innate immune response to MNV
1)
2)
3)
4)

Answer 49

1) MDA5 detects dsRNA, binds IPS1 MAV on mitochondrial surface
2) IRF3/IRF7/NFkB stimulated, enter nucleus
3) IFNab stimulates IFNabR
4) STAT1/STAT2, IRF9 bind, enter nucleus

Question 50

What happens to cells deficient in MDA5 in norovirus infection?

Answer 50

Can’t produce cytokines to combat norovirus infection

Question 51

Part of GIT that norovirus might infect

Answer 51

Peyers patches