Myxoma virus
| Myxoma virus | |
|---|---|
| Virus classification | |
| Group: | Group I (dsDNA) |
| Family: | Poxviridae |
| Genus: | Leporipoxvirus |
| Species: | Myxoma virus |
Myxoma virus is a virus that causes myxomatosis in rabbits and was used as a pest control in Australia.
Virions are enveloped, and have a surface membrane with lateral bodies. The envelope contains host-derived lipids and self-synthesized glycolipids. They are brick-shaped and about 250 nm in diameter, 300 nm in length and 200 nm in height. The middle contains a biconcave core which appears to be characteristic to many poxviruses.
The genome is nonsegmented and contains a single molecule of linear, double-stranded DNA, 160000 nucleotides in length. The genome has a G-C content of ~40%, with terminally redundant sequences which are repeated at both ends.
The genome encodes 170 open reading frames, twelve of which are duplicated in the terminal inverted repetitions.
During their normal life cycles, virions produce extracellular and intracellular proteins. The extracellular proteins are used primarily for suppressing or circumventing the host immune responses, hence are nonessential. Infection is also initiated by extracellular virions. The myxoma virus matures naturally by budding through the surface membrane of the host cell.
The myxoma virus has multiple methods that it utilizes to evade the immune system. One route of protection involves blocking the caspase activity within the host cells. The E13L viral protein is able to inhibit the caspases by binding to the CARD protein, which is part of the caspase-1-activating inflammasome complex. By binding it is able to inhibit apoptosis, which is normally induced by the CARD protein. In addition, the myxoma virus utilizes the Serp-2 viral gene to inhibit a variety of other capsases. The Serp-2 gene is also capable of inhibiting granzyme B, a cysteine protease.
The myxoma virus is also capable of producing tumor necrosis factor receptor mimics to reduce the host's natural response to TNF. The M-T2 protein is a soluble receptor the mimics the TNF receptors within rabbits.
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