| Parapoxvirus | |
|---|---|
 | |
| electron micrograph depicting morphologic variants ofOrf virus | |
Virus classification | |
| (unranked): | Virus |
| Realm: | Varidnaviria |
| Kingdom: | Bamfordvirae |
| Phylum: | Nucleocytoviricota |
| Class: | Pokkesviricetes |
| Order: | Chitovirales |
| Family: | Poxviridae |
| Subfamily: | Chordopoxvirinae |
| Genus: | Parapoxvirus |
| Species | |
Parapoxvirus is a genus ofviruses, in the familyPoxviridae, in the subfamilyChordopoxvirinae.[1] Like all members of the family Poxviridae, they are oval, relatively large, double-strandedDNA viruses. Parapoxviruses have a unique spiral coat that distinguishes them from other poxviruses. Parapoxviruses infectvertebrates, including a wide selection of mammals, and humans.[2]
Not all parapoxviruses arezoonotic. Notable zoonotic hosts of parapoxviruses includesheep,goats, andcattle.
The most recent species of parapoxviruses has been found in New Zealandred deer. There are also some tentativespecies in thegenus, includingAuzduk disease virus,Chamois contagious ecthyma virus, andsealpox virus.
Viruses inParapoxvirus are enveloped, with ovoid geometries. These viruses are about 140–170 nm wide and 220–300 nm long, and have a regular surface structure;tubules with a diameter of 10–20 nm form a criss-cross pattern. Genomes are linear, around 130–150kb in length.[2]
| Genus | Structure | Symmetry | Capsid | Genomic arrangement | Genomic segmentation |
|---|---|---|---|---|---|
| Parapoxvirus | Ovoid | Enveloped | Linear | Monopartite |
Viral replication iscytoplasmic. Entry into the host cell is achieved by attachment of the viral proteins to hostglycosaminoglycans (GAGs) mediatesendocytosis of the virus into the host cell. Fusion occurs with theplasma membrane to release the core into the host cytoplasm. Early phase: early genes are transcribed in the cytoplasm by viralRNA polymerase. Early expression begins at 30 minutes post-infection. Theviral core is completely uncoated as early expression ends, and the viral genome is now free in the cytoplasm. Intermediate phase: Intermediate genes are expressed, triggering genomicDNA replication at approximately 100 minutes post-infection. Late phase: Late genes are expressed from 140 min to 48 hours post-infection, producing all structural proteins. Assembly of progeny virions starts in cytoplasmic viral factories, producing a spherical immature particle. This virus particle matures into brick-shaped intracellular mature virion (IMV). The IMV can be released uponcell lysis, or can acquire a second double membrane from trans-Golgi and bud as external enveloped virion (EEV) host receptors, which mediates endocytosis. Replication follows the DNA strand displacement model. DNA-templated transcription is the method of transcription. The virus exits the host cell by existing in occlusion bodies after cell death and remaining infectious until finding another host. Humans and mammals serve as the natural hosts. Transmission routes arezoonosis and contact.[2]
| Genus | Host details | Tissue tropism | Entry details | Release details | Replication site | Assembly site | Transmission |
|---|---|---|---|---|---|---|---|
| Parapoxvirus | Humans; mammals | None | Glycosaminoglycans | Lysis; budding | Cytoplasm | Cytoplasm | Zoonosis; contact |
The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species:[1]
Parapoxviruses cause infection of cows, sheep, goats, andred squirrels worldwide. They tend to cause lesions that range in size depending on the case. Between 1990 and 1995, there was an average of 15 cases reported annually. This is a significant decline from the annual mean of 46 cases between 1968 and 1978.[citation needed]
Some authors believe that the infection is much more common than reported, as it may not appear to be a serious infection.[citation needed]
Most reports indicate a higher frequency of human infections during the spring and autumn, presumably due to the seasonal slaughtering of susceptible animals. However, others show a higher occurrence in winter. This may be attributed to the use ofgorse, an animal feed that may causetrauma, thereby leading to infection.[citation needed]