“…The primate T-cell lymphotropic viruses (PTLVs), which include human T-cell leukemia virus type 1 (HTLV-1) (21), simian T-cell lymphotropic virus type 1 (STLV-1) (I. Miyoshi, S. Yoshimoto, M. Fujishita, H. Taguchi, I. Kubonishi, K. Niiya, and M. Minezawa, Letter, Lancet ii:658, 1982), HTLV-2 (9), STLV-2 (5,34), and STLV-3 (6), constitute a group of related human and simian retroviruses, sharing common biological and molecular features. Nevertheless, their origin and evolutionary relationship, as well as their modes of dissemination, are still unclear and a matter of discussion (2,4,10,26,29).…”