Subfamily: Spumaretrovirinae

Genus: Felispumavirus

Distinguishing features

Viruses of the genus occur naturally in feline hosts. 

Virion

See discussion in subfamily description. 

Subfamily: Spumaretrovirinae

Genus: Equispumavirus

Distinguishing features

Viruses of the genus occur naturally in equine hosts. 

Virion

See discussion in subfamily description. 

Subfamily: Spumaretrovirinae

Genus: Bovispumavirus

Distinguishing features

Viruses classified as members of the genus colonize bovine hosts. 

Virion

See discussion in subfamily description. 

Family: Retroviridae

Subfamily: Spumaretrovirinae

Subfamily: Orthoretrovirinae

Genus: Lentivirus

Subfamily: Orthoretrovirinae

Genus: Gammaretrovirus

Subfamily: Orthoretrovirinae

Genus: Epsilonretrovirus

Subfamily: Orthoretrovirinae

Genus: Deltaretrovirus

Distinguishing features

Viruses in this genus are most similar to viruses in the genus Gammaretrovirus, but can be distinguished based on RT-based phylogenetic clustering, by the presence of the regulatory genes tax and rex, and in some viruses, the unusual presence of an hbz gene on the antisense strand.

Subfamily: Orthoretrovirinae

Genus: Betaretrovirus

Distinguishing features

Virions can have “B-type” or “D-type” morphology, depending on the species. Genomes typically contain an additional regulatory gene that overlaps with the env gene and is encoded by a multiply-spliced mRNA – examples include the rem gene of MMTV and the rej gene of JSRV. 

Subfamily: Orthoretrovirinae

Genus: Alpharetrovirus

Distinguishing features

Virus particles assemble at the plasma membrane and exhibit a “C-type” morphology. Viruses in the genus have an envelope TM protein with an internal fusion peptide flanked by two cysteines, whereas viruses in the other genera typically have an N-terminal fusion peptide. Many oncogene-containing members of the genus have been isolated.