Poxviruses Flashcards
Poxviruses
2 subfamilies -
chordopoviruses, vertebrates
entomopoxviruses, insects
Orthopox genus
Notably Variola, cowpox, vaccinia and monkeypox
Morphollogically indistinguishable
Immunologically realted
Smallpox
Variola virus - major (20% fatality) and minor (1-2%)
No animal reservoir
300-500 million deaths in 20th century
Symptoms of smallpox
Fever, vomiting, skin rash, mouth ulcers
Variola virus
Large + brick shaped w envelope
1 linear dsDNA genome + hairpin loop at each end
186kbp
Replication occurs in cytoplasm
DNA dependent RNAP
Scarification
Early attempt at vaccine by Edward Jenner
Scratch scabs into arms
Vaccinia virus
Similar to variola
2 types of virion - Mature and Extracellular Enveloped
260 functional proteins
Mature virion (IMV)
Single outer membrane
only released upon cell lysis
responsible for person-person transmission
good at surviving outside of body
Extracellular enveloped virion (EEV)
Membrane dissolution
Fusion with membrane like IMV
Ligand dependent
Endosomal entry with low pH
Poxvirus genome
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
DNA Replication poxviruses
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
Poxvirus transcription
Transcription enzymes packaged into virion core - transcribe early mRNAs
Short promoters not recognised by host RNAP2
Cascade model
Poxvirus transcription cascade model
Expression of each gene class dependent on prior expression of proteins of previous class
Proteins produced in waves
How does the poxvirus cascade model work?
3 stages: early, intermediate and late gene expression
Early gene expression poxvirus
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
Intermediate gene expression
Express DNA replication enzymes
Late gene expression transcription factors
Late gene expression
Structural proteins required to assembly poxvirus particle
Expressed for while then early genes expressed for next particle
Vaccinia replication cycle
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
CEV
Cell associated enveloped virus
Same as EEV but attached to outside of cell
Responsible for cell to cell spread
Vaccinia virus spread
Cell to cell (CEV) and long range spread (EEV)
Plaque assay for vaccinia
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
Model of vaccinia spread in vivo
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
Bioterrorism with smallpox
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
Tecovirimat
Impairs VP37 protein required for envelope development
Virus can’t mature
Inhibits virus induced cytopathic effects
Treatment for symptomatic smallpox
