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Poxviruses (members of the family Poxviridae) are viruses that can, as a family, infect both vertebrate and invertebrate animals.
Four genera of poxviruses may infect humans: orthopox, parapox, yatapox, molluscipox. Orthopox: variola virus, vaccinia virus, cowpox virus, monkeypox virus, smallpox (eradicated); Parapox: orf virus, pseudocowpox, bovine papular stomatitis virus; Yatapox: tanapox virus, yaba monkey tumor virus; Molluscipox: molluscum contagiosum virus (MCV).[1] The most common are vaccinia (seen on Indian subcontinent) and molluscum contagiousum, but monkeypox infections are rising (seen in west and central African rainforest countries).
Poxviridae viral particles (virions) are generally enveloped (external enveloped virion- EEV), though the intracellular mature virion (IMV) form of the virus, which contains different envelope and is also infectious. They vary in their shape depending upon the species but are generally shaped like a brick or as an oval form similar to a rounded brick. The virion size is around 200 nm in diameter and 300 nm in length and carries its genome in a single, linear, double-stranded segment of DNA.[2] By comparison, Rhinovirus is 1/10th as large as a typical Poxviridae virion.[3]
Replication of the poxvirus involves several stages. The first thing the virus does is to bind to a receptor on the host cell surface; the receptors for the poxvirus are thought to be Glycosaminoglycands (GAGs). After binding to the receptor, the virus enters the cell where it uncoats. Uncoating of the virus is a two step process. Firstly the outer membrane is removed as the particle enters the cell; secondly the virus particle (without the outer membrane) is uncoated further to release the core into the cytoplasm. The pox viral genes are expressed in two phases. The early genes are expressed first. These genes encode the non-structural protein, including proteins necessary for replication of the viral genome, and are expressed before the genome is replicated. The late genes are expressed after the genome has been replicated and encode the structural proteins to make the virus particle. The assembly of the virus particle occurs in the cytoskeleton of the cell and is a complex process that is poorly understood but is currently being researched. Considering the fact that this virus is large and complex, replication is relatively quick taking approximately 12 hours. The replication of this virus is unusual for a virus with double stranded DNA genome because it encodes its own machinery for genome replication and therefore the replication occurs in the cytoplasm. Most viruses with a double stranded DNA genome replicate in the nucleus and use the host cells genome replication machinery.
The name of the family, Poxviridae, is a legacy of the original grouping of viruses associated with diseases that produced poxs in the skin. Modern viral classification is based on the shape and molecular features of viruses, and the smallpox virus remains as the most notable member of the family.
The following genera are currently included here:
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