Genus Deltaretrovirus

Type Species	Bovine leukemia virus	(BLV)

Distinguishing Features

Virions are similar to gammaretroviruses in terms of morphology and assembly. Proteins Mr are: MA   ± 19 10³; CA   ± 24 10³; NC   ± 12-15 10³; PR   ± 14 10³; RT; IN; and SU   ± 60 10³; TM   ± 21 10³. The genome is about 8.3  kb in size (one monomer); its organization is illustrated in Figure 5. There are non-structural genes, designated tax, and rex which are involved in regulation of synthesis and processing of virus RNA, in addition to gag, pro, pol and env. The tRNA primer is tRNA^Pro. The LTR is about 550 -750  nts long, of which the U3 region is 200-300  nts, the R sequence 135-235  nts and the U5 region 100-200  nts in size.

The exogenous viruses (horizontal transmission) in this genus are found in only a few groups of mammals. No related endogenous viruses are known. Virus infections are associated with B or T cell leukemias or lymphomas as well as neurological disease (tropical spastic paraparesis, or HTLV-associated myopathy) and exhibit a long latency with an incidence of less than 100%. No oncogene-containing members of this genus have been identified.

List of Species Demarcation Criteria in the Genus

The list of species demarcation criteria is:

	Differences in genome sequence and viral oncogenes,
	Differences in antigenic properties,
	Differences in natural host range,
	Differences in pathogenicity.

HTLV-1 and STLV-1 are not clustered according to host species but rather according to geographic origin. All HTLV-1 subtypes described so far have most probably originated from separate interspecies transmissions from simians to humans. Primate T-lymphotropic virus 1 (PTLV-1) is distinguished from Primate T-lymphotropic virus 2 (PTLV-2) for example primarily on the basis of phylogenetic differences. The two viruses have a similar coding strategy, but only PTLV-1 has been associated with human disease.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Bovine leukemia virus	[K02120]	(BLV)
Primate T-lymphotropic virus 1		(PTLV-1)
Human T-lymphotropic virus 1	[D13784]	(HTLV-1)
Simian T-lymphotropic virus 1		(STLV-1)
Primate T-lymphotropic virus 2		(PTLV-2)
Human T-lymphotropic virus 2	[M10060]	(HTLV-2)
Simian T-lymphotropic virus 2 (Formerly termed STLV-PP)		(STLV-2)
Primate T-lymphotropic virus 3	[Y07616]	(PTLV-3)
Simian T-lymphotropic virus 3 (Formerly termed STLV-L)		(STLV-3)

Tentative Species in the Genus

None reported.