MULTIPLE INTERSPECIES TRANSMISSIONS OF HUMAN AND SIMIAN T-CELL LEUKEMIA LYMPHOMA VIRUS TYPE-I SEQUENCES/

Using two sets of nucleotide sequences of the human and simian T-cell leukemia/lymphoma virus type I (HTLV-I/STLV-I), one consisting of 522 bp of the env gene from 70 viral strains and the other a 140-bp segmen t from the pol gene of 52 viral strains, I estimated cladograms based on a statistical parsimony procedure that was developed specifically t o estimate within-species gene trees. An extension of a nesting proced ure is offered for sequence data that forms nested clades used in hypo thesis testing. The nested clades were used to test three hypotheses r elating to transmission of HTLV/STLV sequences: (1) Have cross-species transmissions occurred and, if so, how many? (2) In what direction ha ve they occurred? (3) What are the geographic relationships of these t ransmission events? The analyses support a range of 11-16 cross-specie s transmissions throughout the history of these sequences. Additionall y, outgroup weights were assigned to haplotypes using arguments from c oalescence theory to infer directionality of transmission events. Conc lusions on geographic origins of transmission events and particular vi ral strains are inconclusive due to small samples and inadequate sampl ing design. Finally, this approach is compared directly to results obt ained from a traditional maximum parsimony approach and found to be su perior at establishing relationships and identifying instances of tran smission.