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Joined 2026-09-21 Message
Orthoretrovirinae 2026-11-05
Orthoretrovirinae is the subfamily of Retroviridae containing Lentivirus and several other retroviral genera. It includes human immunodeficiency virus and feline immunodeficiency virus. The family placement describes a replication strategy; it does not imply one host range or one disease outcome for all members.[ref]
Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Subfamily classification and Distinguishing features
A typical virion packages two copies of its RNA genome. After entry and release of the viral core into a host cell, reverse transcription produces DNA that can become an integrated provirus. Proteolytic processing of a viral polyprotein also releases functional components during maturation.[ref]
Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Distinguishing features, RNA copies, reverse-transcription timing and protease processing
[ref]Retroviridae report by the International Committee on Taxonomy of Viruses. Table 1, replication and integration
An invented counting example clarifies the two-copy description. If each packaged RNA molecule has 10,000 nucleotides, the pair contains 20,000 RNA nucleotides in total. The length of one genome copy is still 10,000 nucleotides. A corresponding 10,000-base-pair double-stranded DNA molecule contains 20,000 DNA nucleotides, but its length is conventionally reported in base pairs. Copy count, nucleotide count and base-pair length answer different questions.
The subfamily's genera are distinguished in part by phylogenetic analysis of conserved reverse-transcriptase regions. A shared enzyme mechanism can coexist with differences in accessory proteins, host distribution and cellular targets. Observing the shared mechanism therefore provides a classification clue while leaving those other biological properties to be determined.[ref]
Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Genus demarcation criteria and differences among members
Spumaretrovirinae 2026-11-05
Spumaretrovirinae is a subfamily of Retroviridae that includes the foamy viruses. The name refers to a characteristic foamy appearance that many isolates produce in cell culture. That visible effect is one observation within a classification also supported by molecular features and phylogenetic analysis.[ref]
Retroviridae report by the International Committee on Taxonomy of Viruses. Derivation of names, Spumaretrovirinae; Relationships within the family
A notable feature concerns the timing of reverse transcription. Released virions can already contain substantial reverse-transcribed DNA. In Orthoretrovirinae, the usual packaged genome is instead two RNA copies and reverse transcription follows entry into a new host cell. Both groups use a DNA stage in their replication cycles.[ref]
Spumaretrovirinae report by the International Committee on Taxonomy of Viruses. Distinguishing features, reverse-transcribed DNA in virions
[ref]Orthoretrovirinae report by the International Committee on Taxonomy of Viruses. Distinguishing features, RNA packaging and post-entry reverse transcription
The ICTV account also describes cytoplasmic capsid assembly and a genome of roughly 11.6 kilobases for a typical spumavirus. Its viral enzyme precursor is expressed from a spliced transcript, rather than the same fused precursor arrangement emphasized for Orthoretrovirinae.[ref]
Spumaretrovirinae report by the International Committee on Taxonomy of Viruses. Distinguishing features, assembly, typical genome and Pro/Pol expression
The timing distinction gives a useful experimental question: at which point in the cycle is a particular nucleic-acid form present? Detecting DNA in released particles and detecting newly made DNA after entry describe different stages. A single positive measurement, without identifying the sampled stage and material, cannot reconstruct when conversion occurred. Molecular form, location and sequence in time are complementary evidence.