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Infectious Diseases > Poxviruses > Flashcards

Poxviruses Flashcards

1
Q

What are the two main subfamilies of poxviruses?

A

Chordopoxvirinae

Entomopoxvirinae

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2
Q

How many genera are there in Chordopoxvirinae?

A

18

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3
Q

What do Chordopoxvirinae infect?

A

vertebrates

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4
Q

How many genera are there in Entomopoxvirinae?

A

4

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5
Q

What do Entomopoxvirinae infect?

A

vertebrates

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6
Q

What is the shape of a poxvirus?

A

oval or “brick”

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7
Q

What is the size of the length of a poxvirus?

A

200-400nm

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8
Q

How would you describe the external surface of a poxvirus?

A

The external surface is ridged in parallel rows, sometimes arranged helically

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9
Q

Are poxviruses weak or resistant to degradation?

A

resistant

can survive in environment for long periods of time

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10
Q

What is the structure of a vaccinia virus like?

A

The outer surface is composed of lipid and protein which surrounds the biconcave (dumbbell-shaped) core, composed of a tightly compressed nucleoprotein, 2 lateral bodies located either side of core.

(dont know purpose of lateral bodies yet)

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11
Q

Which form of mature viron has 2 membranes and which has 1?

A

EEV (extracellular enveloped virions) have 2

IMV (intracellular mature virions) have 1 (only inner membrane)

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12
Q

What is the genome structure of a poxvirus?

A

Linear dsDNA genome of 130-375kb, encodes ~200 proteins

flanked by inverted terminal repeat (ITR) sequences which are covalently-closed at their extremities

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13
Q

How do poxviruses enter a cell?

A

The Entry-Fusion Complex in vaccinia virus located in the outer membrane is formed from 4 types of attachment proteins and 11 different fusion proteins and is required for attachment , membrane fusion and core entry

Uncoating occurs in two stages, removal of the outer membrane as the particle enters the cell and in the cytoplasm, the particle (minus its outer membrane) is further uncoated and the core passes into the cytoplasm

Unusally, attachment to the receptor is NOT the main determinant of cellular tropism in poxviruses like it is for most other viruses

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14
Q

What are the types of temporal gene expression?

A

“early”, “intermediate” & “late” based on times of expression

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15
Q

What type of temporal gene expression is unique to a DNA virus?

A

Early

Occurs in cytoplasm, in partially uncoated core

The template, viral RNA polymerase, and early transcription factors are present within the infectious virus particle

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16
Q

What happens in early phase of temporal gene expression?

A

early genes are transcribed in the cytoplasm by viral RNA polymerase

begins at 30 minutes post-infection

Some products involved in immune evasion

Core is completely uncoated as early expression ends, viral genome is now free in the cytoplasm

17
Q

What happens in the intermediate phase of temporal gene expression?

A

Intermediate genes are expressed, requires products of early genes, triggering genomic DNA replication at approximately 100 minutes post-infection

18
Q

What happens in the late phase of temporal gene expression?

A

Late genes are expressed from 140 min to 48 hours post-infection, requires products of intermediate genes

Production of structural proteins and enzymes that will be packaged in the virions

19
Q

What enzyme makes viral mRNA from viral DNA?

A

Viral RNA polymerase

20
Q

What enzymes cap the viral mRNA?

A

Terminal phosphatase

Guanylyltransferase

N7-Methyltransferase

2’-O-Methyltransferase

21
Q

Where are viral mRNAs made for transcription?

A

cytoplasm

22
Q

Why do viral MRNAs not need splicing?

A

don’t have introns

23
Q

Which end of the viral mRNA of poxviruses has a cap on it during translation?

A

5’

24
Q

Which end of the viral mRNA of poxviruses is polyadenlyated during translation?

A

3’

25
Q

How is the cap-binding complex (eIF4F) is inactivated?

Why?

A

through the cleavage of the eIF4G component (cap binding complex)

to efficiently protein synthesise

26
Q

What covalently connect the ends of each genome?

A

single stranded A-T rich hair pin loops (101nt)

27
Q

Why are hairpin loops and inverted terminal repeats important?

A

for self preservation

28
Q

What is the difference between an immature virion (IV) and an intracellular mature virion (IMV)?

A

IV is spherical and then matures into brick shaped IMV

29
Q

What is an intracellular enveloped virion (IEV)?

A

intracellular mature virion that acquires a seconds membrane from a trans-Golgi or early endosomal compartment

30
Q

Where does assembly of virions occur in the cell?

A

the cytoskeleton

31
Q

What is a cell-associated virion (CEV)?

A

When intracellular enveloped virion (IEV) move to the cell surface on microtubules where fusion with the plasma membrane

32
Q

What is an extracellular enveloped virions (EEV)?

A

cell-associated virion (CEV) induce an actin polymerization that promotes a direct transfer to surrounding cells

33
Q

How does a virion get from once cell to another?

A

Actin filaments have a polarity, with ATP at the growing end.

Virions bind to the ADP end of actin filaments and cause them to extend, propelling the virus outward

Comet tails move fast at 3µm/min and may help spread the virus

34
Q

What are viroceptors?

A

Secreted versions of cellular cytokine receptors

35
Q

What are virokines?

A

Secreted molecules that are either agonistic or antagonistic ligands for host cellular receptors

36
Q

How would you describe Poxvirus host tropisms?

A

Some poxviruses have very narrow host ranges, others infect multiple species

Tropism in cultured cells in vitro is different to in vivo and depends on permissivity rather than specific receptor

37
Q

What is molluscum contagiosum?

A

A human only (keratinocyte) Molluscipoxvirus

Presents as skin blisters and is transmitted via skin to skin contact

Resolves spontaneously or via curretage

38
Q

What is monkeypox?

A

An orthopoxvirus similar to smallpox (~10% mortality)

zoonotic infection (rodents as resevoir host)

Sporadic outbreaks in Central and West Africa

transmission via direct contact of blood, bodily fluids, or cutaneous or mucosal lesions of infected animals

Human to human transmission is generally limited

Diagnosis: Clinical signs, PCR (not serological methods)

Smallpox vaccine provides cross-protection against monkeypox

39
Q

What is smallpox?

A

Two forms: Variola virus major and Variola virus minor

Maculopapular rash – develop into fluid-filled blisters

Major: high mortality (20 – 60%); Minor: Low mortality (1%)

Long term effects: scarring, blindness, osteomyelitis

Transmission: aerosolized droplets, direct contact, fomites

Infectious Diseases (4 decks)

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