# hilal erkan - poxviruses

# **POXVIRUSES**

# Classification
The poxviridae family has two subfamilies:
*Chordopoxviridae (poxviruses of vertebrates), and Entomopoxviridae (poxviruses of insects).*

The subfamily of Chordopoxviridae has nine genera, and four of them can cause the human infections:
*Orthipoxvirus, Parapoxvirus, Molluscipoxvirus, and Yatapoxvirus.*

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# Virion
* Brick-shaped, approximately 250x200x200 nm size
*exception for Parapoxviruses, they are cocoon-shaped with 260x160 nm size*
* The symmetry of the nucleocapsid is either icosahedral or helical
* Complex structure with a core, lateral bodies, outer membrane, and sometimes an envelope
* Most of virions are composed of an outer layer of tubular structures
*exception for Parapoxviruses, they are covered with long thread-like surface tubules*

*Figure 1: Schematic representation of genus Orthopoxvirus and Parapoxvirus*

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# Genome
* Linear double-stranded DNA (dsDNA)
* Genome size 130 kbp (Parapoxviruses) - 375 kbp (Fowlpox virus)
* Have covalent linkages joining ends of the two DNA strand
* The ends of each DNA strand have long inverted tandem repeated nucleotide sequences forming single-stranded loops
* Poxvirus genomes can code for up to 200 proteins
These proteins are coding for virus replication, *nucleic acid synthesis, virion structural component synthesis*
*for example: DNA-dependent DNA polymerase, DNA ligase, DNA-dependent RNA polymerase, and enzymes involved in the capping*

*Figure 2: Structure and organization of the genome of vaccinia virus*

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# Transmission
There are several routes: *by aerosol and droplets, and by introduction of virus into small skin corrosion after contact.*
Poxviruses can resist to the degradation at the ambient temperatures and survive many years in dried scrabs.
All infections caused by poxviruses, associated with localized or widespread lesions of the skin. These lesions can cause many diseases.
Some of the diseases are caused by the different genus of Poxviruses are *Smallpox, Variola major, Variola minor, Vaccinia infection, Human monkeypox, Human cowpox infection, Orf, Yabapox, and Tanapox.*

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# Attachment & Entry
* Viral proteins attach to the host cell membrane glycosaminoglycans (GAGs), and virions are endocytosed into the host cell, or fusion with the plasma membranes can release cores into the host cytoplasm.

Figure 3: The replication cycle of the poxviruses
*MV-mature virion, EV-enveloped virus*

# Early Phase
* Early genes are transcribed in the cytopasm by viral RNA polymerase enzyme. The core is become uncoated when the early expression ends, and viral genome is available in the cytoplasm.

# Intermediate Phase
* Intermediate genes are expressed, and trigger the genomic DNA replication.

# Late Phase
* Late genes are expressed, and produce all the structural proteins.

# Assembly
* Assembly of the virions strart in the cytoplasmic viral factories, and produce a spherical immature particle. This particle matures into the brick-shaped intracellular mature virion.

# Exit
* Intracellular mature virions (MVs) can be released after cell lysis, or can acquire a second double membrane from rhe golgi and bud as external enveloped virions (EVs).