Background:  A serological and molecular survey to evaluate prevalence of STLV infection and STLV diversity within the Tulane National Primate Research Center (TNPRC) captive sooty mangabey colony (Cercocebus atys) was conducted. Colony animals were originally obtained from the Yerkes Primate Research Center (YNPRC) between 1980 and 1990.

Methods:  Animals were bled, serum separated and tested by HTLV antibody ELISA. PBMC DNA was isolated and PCR amplified using viral envelope (env), and LTR specific primers. In addition, 21 wild sooty mangabey bush meat samples from Sierra Leone were also tested.

Results: Approximately 50% of the TNPRC colony samples were STLV-I seropositive. The complete (1460 bp) or partial (522 bp) envelope gene, and the entire LTR (790 bp) were amplified by PCR, Qiagen column purified, and sequenced. Nucleotide sequence alignment and phylogenetic analyses were performed using Clustal W in the Phylip package. Results showed all STLV from the TNPRC colony clustering with the previously reported YNPRC STLV_sm strain. This cluster also included the STLV sequences from the wild sooty mangabeys. Surprisingly, the TNPRC STLV_sm strains separated into 3 distinct subclusters. Given the genetic stability of this virus family, it suggested that at least 3 of the founder sooty mangabeys were infected at the time of their importation from Africa. The STLV_sm sequence from the YNPRC clustered within TNPRC Lineage 2. Genetic distances between the 3 lineages are comparable to those observed in the wild.

Conclusions:  High viral diversity of STLV in the TNPRC colony and interspersion of the wild STLV_sm strains within the colony STLV_sm strain subclusters confirm an African origin for the TNPRC viruses and suggest a Sierra Leone origin for the sooty mangabey colonies in the United States. Similar findings have been shown for SIV_sm diversity. High viral diversity of STLV in the TNPRC colony matches the already reported high diversity of SIV_sm, however, the lack of correlation between lineage distribution of the strains of SIV and STLV suggests that the intracolony transmission of the 2 viruses followed different mechanisms. Given the geographical clustering of PTLV-I strains in Africa, study of HTLV-I diversity in Sierra Leone will be necessary to confirm STLV_sm potential for cross-species transmission to humans, as reported for SIV_sm and HIV-2.                

Keywords: STLV-I; sooty mangabey; Sierra Leone