Foamy virus

Overview

Foamy viruses, also known as spumaviruses, are a group of complex retroviruses that belong to the subfamily Spumaretrovirinae within the family Retroviridae. They are named for the characteristic foamy appearance of the infected cells in culture. Unlike other retroviruses, foamy viruses are not known to cause disease in their natural hosts, which include a variety of mammals such as non-human primates, cats, cattle, and horses.

Virology

Structure

Foamy viruses have a typical retroviral structure, consisting of an envelope, a capsid, and a single-stranded RNA genome. The envelope is derived from the host cell membrane and contains viral glycoproteins that facilitate entry into host cells. The capsid encases the viral RNA and associated proteins necessary for replication.

Genome

The foamy virus genome is approximately 12-14 kilobases in length and contains the typical retroviral genes: gag, pol, and env. In addition, foamy viruses have unique accessory genes such as tas (transactivator of spumaviruses) and bet, which are involved in viral replication and immune evasion.

Replication Cycle

The replication cycle of foamy viruses is similar to that of other retroviruses but with some unique features. After entry into the host cell, the viral RNA is reverse transcribed into DNA by the viral reverse transcriptase. This DNA is then integrated into the host genome. Unlike other retroviruses, foamy viruses can initiate reverse transcription in the virion before entry into the host cell. The integrated provirus is transcribed by the host's RNA polymerase II, leading to the production of new viral RNA and proteins.

Pathogenesis

Foamy viruses are generally considered non-pathogenic in their natural hosts. They establish persistent infections without causing apparent disease. This characteristic makes them of interest for potential use in gene therapy and vaccine development.

Epidemiology

Foamy viruses are endemic in many mammalian species. In non-human primates, infection rates can be high, but transmission to humans is rare and usually occurs through direct contact with infected animals. Human infections have been documented, but no associated diseases have been identified.

Clinical Significance

While foamy viruses are not known to cause disease, their ability to integrate into the host genome and persist without causing harm makes them valuable tools for molecular biology research. They are being explored as vectors for gene therapy due to their stable integration and low pathogenicity.

Research and Applications

Foamy viruses are used in research to study viral replication, host-virus interactions, and the development of viral vectors for gene therapy. Their unique replication cycle and non-pathogenic nature make them ideal candidates for these applications.

See Also

• Retrovirus
• Gene therapy
• Viral vector

External Links

• [Foamy Virus Database]
• [Retroviridae Family Overview]