Phylogenetic Analysis of Simian T-lymphotropic Virus Type I (STLV-I) in Common Chimpanzees (Pan troglodytes): Evidence for Interspecies Transmission of the Virus between Chimpanzees and Humans in Central Africa

AbstractSerum and peripheral blood leukocytes from the chimpanzees (Pan troglodytes) of the colony of the Laboratory of Central Nervous System Studies, National Institute of Neurological Disorders and Stroke, NIH, were tested for the presence of STLV-I-specific antibodies and proviral DNA. Antibodies were determined by gelatin particle agglutination and Western blot (WB) assays utilizing HTLV-I antigens. Proviral DNA was detected by four PCR assays targeting three different regions of STLV-I genome: the fragments of theenvandpolgenes andLTR.Twenty of twenty-two DNA samples from WB-positive animals were PCR positive. None of the DNA samples from WB-negative (n= 5) and WB-indeterminate (n= 4) animals was PCR positive. The results of the nested and double nestedenvPCR tests were fully concordant; the seminestedLTRPCR test was much less sensitive. The DNA sequences from theenv(483 bp) and thepol(200 bp) genes andLTR(705 bp) were determined for six, two, and two chimpanzee STLV-I isolates, respectively. Phylogenetic analysis revealed that chimpanzee STLV-I isolates can be attributed to three clades. The first of these clades (SS-PTR1/CSA) included STLV-I isolates from the chimpanzees and West African subspecies of African green monkeys (Cercopithecus a. sabaeus). The other clades (S-PTR2 and S-PTR3) included STLV-I isolates only from chimpanzees. However, both S-PTR2 and S-PTR3 clustered together with Central African HTLV-I comprising the human/simian clade (HS-HSA/PTR). This pattern of phylogenetic clustering suggests that interspecies transmission of STLV-I occurred between chimpanzees and African green monkey subspecies as well between chimpanzees and human populations in Central Africa