Poxviruses

Question 1

Poxviruses

Answer 1

2 subfamilies -
chordopoviruses, vertebrates
entomopoxviruses, insects

Question 2

Orthopox genus

Answer 2

Notably Variola, cowpox, vaccinia and monkeypox
Morphollogically indistinguishable
Immunologically realted

Question 3

Smallpox

Answer 3

Variola virus - major (20% fatality) and minor (1-2%)
No animal reservoir
300-500 million deaths in 20th century

Question 4

Symptoms of smallpox

Answer 4

Fever, vomiting, skin rash, mouth ulcers

Question 5

Variola virus

Answer 5

Large + brick shaped w envelope
1 linear dsDNA genome + hairpin loop at each end
186kbp
Replication occurs in cytoplasm
DNA dependent RNAP

Question 6

Scarification

Answer 6

Early attempt at vaccine by Edward Jenner
Scratch scabs into arms

Question 7

Vaccinia virus

Answer 7

Similar to variola
2 types of virion - Mature and Extracellular Enveloped
260 functional proteins

Question 8

Mature virion (IMV)

Answer 8

Single outer membrane
only released upon cell lysis
responsible for person-person transmission
good at surviving outside of body

Question 9

Extracellular enveloped virion (EEV)

Answer 9

Membrane dissolution
Fusion with membrane like IMV
Ligand dependent
Endosomal entry with low pH

Question 10

Poxvirus genome

Answer 10

Variable - Conserved - Variable
Variable: Non-essential functions -> host range, virulence and immunomodulation
Conserved: Essential functions -> trancription, DNA replication, structural proteins, enzymes
dsDNA 135-300kbp
Tightly packaged

Question 11

DNA Replication poxviruses

Answer 11

Occurs in cytoplasm
Starts with nick at ends of genome, self priming
Continuous ORF
Highly conserved proteins e.g. DNAP, NTP, DNA glycolase
Semiconservative replication

Question 12

Poxvirus transcription

Answer 12

Transcription enzymes packaged into virion core - transcribe early mRNAs
Short promoters not recognised by host RNAP2
Cascade model

Question 13

Poxvirus transcription cascade model

Answer 13

Expression of each gene class dependent on prior expression of proteins of previous class
Proteins produced in waves

Question 14

How does the poxvirus cascade model work?

Answer 14

3 stages: early, intermediate and late gene expression

Question 15

Early gene expression poxvirus

Answer 15

Driven by transcription factors already present in virion
They come into the cell with the virion particle
Package the early transcription system within the infectious virus particle and sequentially synthesizing virus-encoded intermediate and late transcription factors

Question 16

Intermediate gene expression

Answer 16

Express DNA replication enzymes
Late gene expression transcription factors

Question 17

Late gene expression

Answer 17

Structural proteins required to assembly poxvirus particle
Expressed for while then early genes expressed for next particle

Question 18

Vaccinia replication cycle

Answer 18

Microtubule network usd to move around the cell
IMV released by lysis - small proportion to golgi
golgi wraps in double membrane = IEV 3 membranes
Buds out, loses one of membrane and forms CEV

Question 19

CEV

Answer 19

Cell associated enveloped virus
Same as EEV but attached to outside of cell
Responsible for cell to cell spread

Question 20

Vaccinia virus spread

Answer 20

Cell to cell (CEV) and long range spread (EEV)

Question 21

Plaque assay for vaccinia

Answer 21

Lawn of bacteria, plaque = region on plate infected by virus
Important for determining how particles can be fatal
Titrate 10 fold dilution until you see individual plaques on plate
1 plaque = 1 viral particle, can determine how many per ml
Too fast for vaccinia plaque assay

Question 22

Model of vaccinia spread in vivo

Answer 22

Virus promotes actin tail formation
actin tail propels CEV onto adjacent cell
Cell marked with A36/33 to indicate it has been infected - prevent waste of resources
Bouncing continues to next uninfected cell - VERY FAST

Question 23

Bioterrorism with smallpox

Answer 23

Possibly unregistered stocks globally
Reduced immunity in public due to vaccine campaign being stopped
Antiviral treatments such as tecovirimat used to contain and normal pandemic procedures

Question 24

Tecovirimat

Answer 24

Impairs VP37 protein required for envelope development
Virus can’t mature
Inhibits virus induced cytopathic effects
Treatment for symptomatic smallpox

Question 25

Monkeypox

Answer 25

Usually mild illness
Less fatal than smallpox
attenuated vaccinia ankara vaccine
human-human transmission through bodily fluids