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MICB 202 - Virology > Topic 2 > Flashcards

Topic 2 Flashcards

(78 cards)

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1
Q

Picornavirus - What is the etymology?

A 
Pico = Greek for VERY SMALL
RNA = for RNA (made of RNA)
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2
Q

How many genera of picornaviuses are there?

A

5 genera - poliovirus is a picornavirus

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3
Q

What genus does Poliovirus belong in?

A

Enterovirus (goes through intestine)

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4
Q

Where does poliovirus usually become implanted?

A

They usually are implanted in the lower intestinal tract, but undergo limited replication in the oropharynx (middle of pharynx)

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5
Q

What properties do enteroviruses have, in terms of acid/chemical resistance?

A
  • Acid stable (can suvive at pH 3 and lower) to pass through stomach
  • Resistant to most laboratory disinfectants
  • Sensitive to formaldehyde
  • Sensitive to chlorine at levels 0.3-0.5 ppm
  • Inorganic matter can protect from inactivation
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6
Q

What disease does poliovirus cause?

A

paralytic poliomyelitis (inflammation of the spinal cord/motor neurons due to poliovirus resulting in paralysis)

Characterized by flaccid muscular paralysis

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7
Q

Of those who get infected by poliovirus, how many cases result in the clinical disease (i.e. disease with symptoms that can be detected)?

A

1%

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8
Q

What does the poliovirus gene consist of? (i.e. Nucleotide type, + or -, modifications)

A

Single-stranded +-sense RNA, modified with a basic VPg protein (~23AA long) at the 5’ end and a polyA tail at the 3’ end

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9
Q

What are some properties of the poliovirus genome?

A
  • Infection genomic RNA (injection of RNA will result in virus progeny)
  • has a long 5’ UTR and shorter 3’ UTR
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10
Q

What is the function of the poliovirus UTR’s?

A

5’ UTR is important for translation of RNA and the packing of the genome

3’ UTR is important in the syntehsis of a (-) strand for genome replication

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11
Q

What protein does the poliovirus genome encode for?

A

It incodes a single polyprotein 2100-2400 AA long. Polyprotein is cleaved by 2 viral-encoded proteases to produce 20 different structural and non-structural proteins

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12
Q

What is the structure of the poliovirus virion?

A

Non-enveloped (naked)

27-30 nm in diameter

Packed in icosahedral capsid of 20 capsomers, with sodium or potassium ions inside (to balance -ve
phosphate charge on RNA

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13
Q

What is the structure of the poliovirus capsomers?

A

Made of three triangular subunits (VP0, VP1, VP3)

VP0 splits into 2 sub-subunits during maturation; VP2 (on outside of capsid) and VP4 (inside of capsid)

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14
Q

What is the host range of poliovirus?

A

Humans are the only known poliovirus reservoir; spread by human contact

Mouse cells cannot be infected

Transformed monkey cells CAN be infected

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15
Q

What is the receptor for poliovirus? Antireceptor/virus receptor?

A

CD155 (belongs in Ig gene superfamily; relatives include CD4, CD8, MHC class I and II)

Anti-receptor is called “PVR” (poliovirus receptor

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16
Q

Where can the receptor for poliovirus be found?

A

CD155 (the receptor) can be found on moncytes, macrophages, thymocytes, and CNS neurons

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17
Q

What is the number of capsomers in immature poliovirus? Mature?

A

20 for both

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18
Q

What is the number of protomers in immature poliovirus? Mature?

A

203=60 (in both immature and mature proteins (oligomeric subunits, so since there are 3 “main” units of capsomers, we do 203)

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19
Q

What are the structural proteins found in immature poliovirus? Mature?

A

Immature: VP0, VP1, VP3
Mature: VP1, VP2, VP3, VP4

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20
Q

What is the total number of proteins in immature poliovirus? Mature?

A

Immature: 603 =180
Mature: 604=240

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21
Q

What is the first step of the poliovirus replication cycle?

refer to pg 26’s diagram

A

Poliovirus binds to CD155 of a susceptible cell, causing conformational change in VP1 protein such that it can insert itself into the lipid bilayer of the host cell. This forms a transmembrane pore for the viral RNA to leave the capsid and enter the cytoplasm

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22
Q

How does the poliovirus capsid rearrange during the confirmation change when binding?

A

VP2 and VP4 N-terminus become exposed, creating an altered virus particle (160S → 135S) that is more sensitive to low pH and proteases

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23
Q

What occurs during the second step of poliovirus replication?
(refer to pg 26’s diagram)

A

Cellular enzyme cleaves of VPg molecule attached to 5’ end of poliovirus genome. Uses the cellular ribosomes to translate genome at start site 741 nucleotide away from 5’ end

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24
Q

How does poliovirus get around the lack of a 5’ cap?

A

Poliovirus RNA folds in upon itself, forming H-bonds between complementary bases to form the Internal Ribosome Entry Site (IRES). IRES allows the ribosome to assemble on 5’ end of RNA

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25
What happens in step 3-5 in the replication of poliovirus? | refer to pg 26's diagram
Polyprotein is synthesized and folds. Part of the protease becomes an active protease that cleaves part of the polyprotein. Replication complexes (RNA-dependent RNA polymerase (RDRP), VPg, and the genomic strand of RNA associate with cellular membrane structures to form a "replication compartment" formed by virus modification of the ER
26
What are important products produced by cleavage of the polyprotein, and what are their functions?
VPg (for newly synthesized poliovirus genome) RNA-dependent RNA polymerase (RDRP) - for replication of poliovrius genome and viral mRNA synthesis Proteins required to make capsid Protease (P2A) that damage the cap-binding structure of cellular mRNA
27
What happens in step 6-10 in the replication of poliovirus? (refer to pg 26's diagram)
RNA is sythesized in the "replication compartments" by copying the (+)-strand to form the (-)-strand, then using the (-)-strand to produce more (+)-strands. Some (+)-strands are used in protein synthesis by cellular ribosomes, while others are used for the progeny viruses.
28
What happens in step 11 in the replication of poliovirus? (refer to pg 26's diagram)
VP0, VP1, and VP3 coming from the cleavage of the polyprotein associate with one another, forming the pro-capsid. Viral genome is inserted into pro-capsid. Assembly occurs spontaneously once a critical level of protein is reached
29
What happens in step 12 in the replication of poliovirus? (refer to pg 26's diagram)
(+)-strand of RNA is localized to capsid proteins by interaction between packagin site (PAC site) and capsid proteins, ensuring that it is the (+) strand and not (-) strand or cellular mRNA that is packaged. After insertion, RNA genome catalyzes VP0 cleavage into VP2 and VP4 (acting as a ribozyme; RNA with enzymatic activity) This seals the capsid, protecting the RNA from degradation
30
What is the name for the packaging and cleavage process in step 12 of poliovirus replication?
Maturation
31
What happens in step 13 in the replication of poliovirus? (refer to pg 26's diagram)
Poliovirus is released from cytoplasm when the host cell lyses
32
How does poliovirus compete with cellular mRNA?
Apart from forming the IRES (internal riboseome entry site), the virus shuts off cellular protein synthesis using P2A protease
33
What does P2A target?
Targets the "Cap-binding complex" (CBC) of the cell, specifically the eukaryotic translation initiation factor 4G (eIF4G)
34
What is the role of eIF4G, and what is the effect of eIF4G cleavage?
eIF4G is a scaffolding protein that bridge eIF3 (connected to 40S ribosome) and cap-binding protein (eIF4E). By cleaving eIF4G, cellular mRNA cannot bind and be translated as they lack an IRES to compensate (unlike the
35
What is the primer for Poliovirus RDRP? What is its sequence, and where does it attach to?
VPg primer (with covalently attached nucleotides) acts as the primer. The sequence is 5'-pUpU-OH-3' (p-phosphate, U is uracil). binds to the polyA tail of the (+) strand
36
What occurs during the process of (+) strand replication?
VPg is bound ti (+) strand and used as a primer to synthesize the (-) complementary strand (AKA replicative intermediate) (-) strand is bound by another VPg, which acts as a primer for RDRP to synthesize new (+) strand viral RNA
37
By what method does poliovirus enter the body?
Alimentary tract (via mouth)
38
What is the incubation period of poliovirus?
7-14 days
39
Where is the primary site of infection for poliovirus?
lymphoid tissue associated with oropharynx (throat) and gut
40
What is transient viremia?
Virus in the bloodstream
41
What does transient viremia, caused by infection of poliovirus, cause?
Delivers virus to target organs of the CNS, where it infects certain nerve cells and damages or destroys these cells during replication
42
How long does the virus persist after infection (clinical or subclinical infections; i.e. w/ or w/o symptoms)
1-2 weeks after infection
43
How is the poliovirus transmitted?
Fecal-oral route, for several weeks after the infection
44
What are the four responses that can result from the poliovirus?
Subclinical infection (asymptomatic infection) Mild illness (abortive polio) Non-paralytic poliomyelitis (AKA aseptic meningitis, or meningitis free of infection) Paralytic poliomyelitis
45
What is abortive polio characterized by?
Febrile illness with non-specific symptoms such as fever, malaise, drowsiness, headache, nausea, vomiting, and sore throat (cold-like illness) complete recovery in a few days (~72 hours) Only recognized and confirmed if poliovirus is present in the blood Most common case (95% of cases)
46
What is aseptic meningitis (Non-paralytic polio) characterized by?
Same symptoms of abortive polio, + stiffness & pain in neck and back that lasts for 2-10 days. Similar recovery. with abortive polio (influenza-like symtoms) 1-2% of infections
47
What is paralytic polio characterized by?
Flaccid paralysis (weakness in muscles) caused by lower motor neuron damage from poliovirus. May follow minor illness, but usually occurs without minor illness. Damage varies from case to case. Maximal recovery usually occurs within 6 months >0.5% of infections
48
Are antibodies present during poliovirus infection?
Yes; it appear early in infection, and usually present during pralysis
49
What is Post poliomyelitis muscle atrophy (PPMA)?
PPMA is a "reappearance" of paralysis and muscle wasting appearing in patients decades after illness and recovery from paralytic poliomyelitis (specifically) NOT a consequence of persistent infection Result in decline in function of motor neurons that had compensated for the loss in function of motor neurons killed by prior poliovirus infection
50
What were methods used to control polio infection BEFORE the development of a vaccine? How effective were they?
Passive immunization (giving Ab from someone who has had polio to someone at risk, for temporary protection) Non-specific health measure (i.e. patient isolation, closure of public places) Not successful in preventing epidemics
51
What is a serotype?
A variant of a virus that will cause the production of a DISTINCT population of antibodies
52
How many poliovirus serotypes are there? What is the differences between them?
3 (1, 2, 3 are the stereotypes) Serotype 1 is the most virulent, serotype 2 is the next most virulent (successfully eradicated) serotype 3 is the least, causing a small but significant amount of cases All 3 can cause paralytic polio
53
What are the epitopes responsible for causing an immunogenic response against poliovirus?
VP1, VP2, and VP3 on the capsid (most Ab are against VP1)
54
Would Ab against VP1 from a serotype 1 poliovirus work on VP1 from a serotype 2 poliovirus?
No, it will not. They are slightly different structures and Ab will not bind to the serotype 2 VP1
55
What are the 2 forms of poliovirus vaccines?
IPV (Inacitvated Poliovirus Vaccine, injected) | OPV (Oral poliovirus vaccine, injested as syrup)
56
How is IPV vaccine produced and administered?
Poliovirus serotypes are cultivated using monkey kidney cells or human cell lines Viruses concentrated, purified, inactivated w/ formaldehyde Administered by injection; requires boosters
57
What are advantages of IPV?
- Confers humoral immunity (IgG produced) | - No live virus, so potential for reversion to virulence not possible, allowing use in immunosuppressed individuals
58
What are disadvantages of IPV?
- Does not confer localized immunity (i.e. no secretion of IgA in GI tract), meaning vaccinated people are able to be infected by poliovirus in their GI tract (not bloodstream) and possibly transmit wild Poliovirus (through shedding) - Booster shots are required to maintain effectiveness
59
How is OPV produced and administered?
Attenuated "live" strains from 2 poliovirus serotypes are cultivated from monkey kidney cell culture. Virus is orally ingested, and the attenuated virus infects & replicates in host
60
What is attenuation?
A procedure that selects for non-virulent strains of a pathogen that still immunogenic
61
What are the advantages of IPV?
Confers humoral and intestinal immunity (i.e. IgG and IgA production) Induces Ab production quickly, requires no boosters, and is easily administered Cheap to produce & administer (doesn't require lots of training to administer, nor does it require sterile equipment (needles))
62
What are disadvantages of OPV?
Virus can mutate and (RARELY) revert back to neurovirulence that causes paralytic polio in vaccine recipient or susceptible contacts Vaccine progeny spreads to others in contact (household) - progeny is likely mutated and may not be as safe as the original attenuated virus Cannot be given to immunodeficient or immunosuppressed individuals or members of their household (for the above reason)
63
What is a proposed solution to overcome the problems of IPV and OPV?
Proposal is to administer IPV first, then OPV as a booster - this means that if OPV reverts back, IPV-induced Ab will protect against virus, while conferring both humoural and intestinal immunity
64
Who developed IPV + year?
Jonas Salk, in the 1950s
65
Who developed OPV + year?
Albert Sabin, in the 1960s
66
Family-genus of poliovarus?
Picornavirus - enterovirus
67
Baltimore classification of poliovirus?
RNA virus (IV)
68
Genome of poliovirus?
(+) ssRNA
69
Genome Pieces of poliovirus?
1 piece/molecules
70
Is the poliovirus naked or enveloped?
Naked
71
Are there any enzymes packed in poliovirus virions?
No
72
Site of replication for poliovirus?
Cytoplasm
73
Host cell range of poliovirus?
Human intestinal epithelial cells and neurons
74
Route of infection for poliovirus?
Fecal-oral
75
Vaccine approaches to Poliovirus?
Inactivated, injected vaccine (IPV) | Live, attenuated oral vaccine (OPV)
76
What risk factors increase the likelihood of paralysis in Poliovirus cases?
``` Immune deficiency Preganancy Removal of the tonsils Intramuscular injections (ex. medications) Strenuous exercise Injury Age (increased age increases likelihood) ```
77
How is poliovirus treated?
Mainly symptom relief and complication reduction: - Moist heat for muscle spasms and pain - Medication for pain - Iron lung for those who can't breathe (paralysed lung) - Long term rehab (e.g. physiotherapy) - Control (i.e. isolation, closing schools, etc.)
78
Can muscle control be regained?
In some cases, yes. However, Post-polio syndrome may result in muscle weakness prematurely than a normal person

MICB 202 - Virology (3 decks)

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