Complete sequence of a novel highly divergent simian T-cell lymphotropic virus from wild-caught red-capped mangabeys (Cercocebus torquatus) from Cameroon: a new primate T-lymphotropic virus type 3 subtype

Abstract

Among 65 samples obtained from a primate rescue center located in Cameroon, two female adult red-capped mangabeys (Cercocebus torquatus) (CTO-602 and CTO-604), of wild-caught origin, had a peculiar human T-cell lymphotropic virus type 2 (HTLV-2)-like Western blot seroreactivity (p24, RGD21, +/-K55). Analyses of the simian T-cell lymphotropic virus type 3 (STLV-3)/CTO-604 complete proviral sequence (8,919 bp) indicated that this novel strain was highly divergent from HTLV-1 (60% nucleotide similarity), HTLV-2 (62%), or STLV-2 (62%) prototypes. It was, however, related to STLV-3/PH-969 (87%), a divergent STLV strain previously isolated from an Eritrean baboon. The STLV-3/CTO-604 sequence possesses the major open reading frames corresponding to the structural, enzymatic, and regulatory proteins. However, its long terminal repeat is shorter, with only two 21-bp repeats. Furthermore, as demonstrated by reverse transcriptase PCR, this new STLV exhibits significant differences from STLV-3/PH-969 at the mRNA splice junction position level. In all phylogenetic analyses, STLV-3/CTO-604 and STLV-3/PH-969 clustered in a highly supported single clade, indicating an evolutionary lineage independent from primate T-lymphotropic virus type 1 (PTLV-1) and PTLV-2. Nevertheless, the nucleotide divergence between STLV-3/PH-969 and STLV-3/CTO-604 is equivalent to or higher than the divergence observed between the different HTLV-1 or HTLV-2 subtypes. Thus, the STLV-3/CTO-604 strain can be considered the prototype of a second subtype in the PTLV-3 type. The presence of two related viruses in evolutionarily distantly related African monkeys species, living in two opposite ecosystems (rain forest versus desert), reinforces the possible African origin of PTLV and opens new avenues regarding the search for a possible human counterpart of these viruses in individuals exhibiting such HTLV-2-like seroreactivities.

Figures

FIG. 1.

(A) PCR strategy for amplifying the entire STLV-3/CTO-604 proviral genome. The nine proviral fragments which were amplified by PCR, cloned, and sequenced are shown (black bars). (B) Schematic representation of the STLV-3/CTO-604 proviral genome (top) and of the resulting viral messengers (bottom). The start codon used for the translation of the precursor protein (asterisks), the primers used for detection of singly spliced or doubly spliced messengers (horizontal arrows), and the positions and designations of the spliced sites (vertical arrows) identified in the STLV-3/CTO-604 genome are indicated. Nucleotide numbering is according to the STLV-3/CTO604 proviral genome. sa, splice acceptor; sd, splice donor.

FIG. 2.

Western blot serological patterns of the two C. torquatus animals from Cameroon, using the Western blot from Diagnostic Biotechnology (HTLV blot version 2.4). Lane 1, HTLV-1 positive control; lane 2, HTLV-2 positive control; lane 3, HTLV-1 and -2 negative control; lane 4, plasma from CTO-604; lane 5, plasma from CTO-602.

FIG. 3.

Unrooted phylogenetic tree generated by the NJ method on the Tax amino acid sequences (aa 1 to 331 of the HTLV-2A MO prototype sequence). Bootstrap support (1,000 replicates) for the NJ tree is noted on the branches of the tree. The STLV-3/CTO-604 and STLV-3/CTO-602 sequences were analyzed with HTLV and STLV prototype sequences available from the GenBank database (26). Branch lengths are proportional to the evolutionary distance (scale bar) between the taxa.

FIG. 4.

Unrooted phylogenetic tree generated by the NJ method on the Env polyprotein nucleotide sequence (nt 1 to 1467 of the HTLV-1A ATK prototype sequence). Bootstrap support (1,000 replicates) for the NJ tree is noted on the branches of the tree. The STLV-3/CTO-604 strain was analyzed with HTLV and STLV prototype sequences available from the GenBank database (26). Branch lengths are proportional to the evolutionary distance (scale bar) between the taxa.