Identification in gelada baboons (Theropithecus gelada) of a distinct simian T-cell lymphotropic virus type 3 with a broad range of Western blot reactivity

Abstract

Antibodies to simian T-cell lymphotropic virus (STLV) were found in serum or plasma from 12 of 23 (52·2 %) gelada baboons (Theropithecus gelada) captive in US zoos. A variety of Western blot (WB) profiles was seen in the 12 seroreactive samples, including human T-cell lymphotropic virus (HTLV)-1-like (n=5, 41·7 %), HTLV-2-like (n=1, 8·3 %), HTLV-untypable (n=4, 33·3 %) and indeterminate (n=2, 16·6 %) profiles. Phylogenetic analysis of tax or env sequences that had been PCR amplified from peripheral blood lymphocyte DNA available from nine seropositive geladas showed that four were infected with identical STLV-1s; these sequences clustered with STLV-1 from Celebes macaques and probably represent recent cross-species infections. The tax sequences from the five remaining geladas were also identical and clustered with STLV-3. Analysis of the complete STLV-3 genome (8917 bp) from one gelada, TGE-2117, revealed that it is unique, sharing only 62 % similarity with HTLV-1/ATK and HTLV-2/Mo. STLV-3/TGE-2117 was closest genetically to STLV-3 from an Eritrean baboon (STLV-3/PH969, 95·6 %) but more distant from STLV-3s from red-capped mangabeys from Cameroon and Nigeria (STLV-3/CTO-604, 87·7 %, and STLV-3/CTO-NG409, 87·2 %, respectively) and Senegalese baboons (STLV-3/PPA-F3, 88·4 %). The genetic relatedness of STLV-3/TGE-2117 to STLV-3 was confirmed by phylogenetic analysis of a concatenated gag-pol-env-tax sequence (6795 bp). An ancient origin of 73 628–109 809 years ago for STLV-3 was estimated by molecular clock analysis of third-codon positions of gag-pol-env-tax sequences. LTR sequences from five STLV-3-positive geladas were >99 % identical and clustered with that from a Papio anubis×P. hamadryas hybrid Ethiopian baboon, suggesting a common source of STLV-3 in these sympatric animals. LTR sequences obtained 20 years apart from a mother–infant pair were identical, providing evidence of both mother-to-offspring transmission and a high genetic stability of STLV-3. Since STLV-3-infected primates show a range of HTLV-like WB profiles and have an ancient origin, further studies using STLV-3-specific testing are required to determine whether STLV-3 infects humans, especially in regions of Africa where STLV-3 is endemic.