Spumavirus

A genus of retroviruses known for their unique replication process

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Spumavirus
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Family:	Retroviridae

Spumavirus is a genus of viruses within the family Retroviridae. These viruses are commonly referred to as foamy viruses due to the characteristic cytopathic effect they induce in cell cultures, which appears foamy under a microscope. Spumaviruses are unique among retroviruses because of their complex replication cycle and the fact that they are not known to cause disease in their natural hosts.

Characteristics

Spumaviruses are enveloped viruses with a positive-sense, single-stranded RNA genome. Unlike other retroviruses, spumaviruses have a complex genome organization that includes additional open reading frames (ORFs) beyond the typical gag, pol, and env genes found in other retroviruses. These additional ORFs encode accessory proteins that are involved in the regulation of viral replication and host interaction.

Genome and Structure

The genome of spumaviruses is approximately 12-14 kilobases in length. It contains the standard retroviral genes:

• gag – encodes the group-specific antigen proteins that form the viral core.
• pol – encodes the reverse transcriptase, integrase, and protease enzymes necessary for viral replication.
• env – encodes the envelope glycoproteins that facilitate viral entry into host cells.

In addition to these, spumaviruses have unique accessory genes such as tas (transactivator of spumavirus) and bet, which play roles in transcriptional activation and immune evasion, respectively.

Replication Cycle

The replication cycle of spumaviruses is distinct from other retroviruses. After entry into the host cell, the viral RNA is reverse transcribed into DNA, which is then integrated into the host genome. However, unlike other retroviruses, spumaviruses can also produce DNA in the cytoplasm, which is a unique feature. The integrated viral DNA serves as a template for the production of new viral RNA and proteins, which are assembled into new virions that bud from the host cell.

Pathogenicity

Spumaviruses are generally considered non-pathogenic in their natural hosts, which include a variety of mammals such as primates, cats, and cattle. Despite their ability to infect human cells in vitro, there is no evidence that spumaviruses cause disease in humans. This has made them a subject of interest for gene therapy and vaccine vector research.

Research and Applications

Due to their unique properties and non-pathogenic nature, spumaviruses are being studied as potential vectors for gene therapy. Their ability to integrate into the host genome and express transgenes makes them attractive candidates for delivering therapeutic genes.

Also see

• Retrovirus
• Lentivirus
• Oncovirus
• Gene therapy
• Viral vector