It is now recognized that STLV-3, originally isolated from a captive hamadryas baboon (, respectively) (9, 41).Collectively, members of the HTLV groups and their STLV analogues are called primate T-lymphotropic viruses (PTLV); PTLV-1, PTLV-2, and PTLV-3 are composed of HTLV-1 and STLV-1, HTLV-2 and STLV-2, and HTLV-3 and STLV-3, respectively.
Molecular dating estimates that the ancestor of HTLV-3 is as old as HTLV-1 and HTLV-2, with an inferred divergence time of 36,087 to 54,067 years ago.
Although an STLV-2 has been identified in two troops of captive bonobos (), the zoonotic relationship of this virus to HTLV-2 is less clear (10, 40).
Recently, two new HTLVs, HTLV-3 and HTLV-4, were identified in primate hunters in Cameroon, expanding substantially the diversity of deltaretroviruses in humans.
The secondary structure of the LTR RNA was determined using the RNAstructure program, version 4.2 (19).
Sequences were aligned using the Clustal W program (36), gaps were removed, and distance-based trees were generated using the Kimura two-parameter model together with the neighbor-joining method in the MEGA program (version 2.1) and maximum-likelihood (ML) analysis in the PAUP* program as described in detail elsewhere (34, 43).