Abstract
<jats:p>Background Human T-lymphotropic virus type 1 (HTLV-1) is an oncogenic retrovirus which is transmitted via cell-containing blood products or from mother to child via breastfeeding, leading to severe diseases such as adult T-cell leukemia/lymphoma (ATL) and neuroinflammation. Most studies focus on virus detection in peripheral blood due to limited access of tissue material, especially in infants. Thus, our understanding of viral distribution in organs, in particular along the oral route of transmission, is still a critical gap in HTLV-1 research. Methodology/Principal Findings Here, we present an analysis of tissues from a non-human primate (NHP) colony (olive baboon: Papio anubis) naturally infected with the closely related counterpart of HTLV-1, simian T-lymphotropic virus type 1 (STLV-1). Various organs and tissues of the oropharyngeal and gastrointestinal tract including tonsils, stomach, small intestine and colon were analyzed for the presence or absence of STLV-1. Beside TaqMan qPCR measuring relative copy numbers, we established a highly sensitive and precise droplet digital (dd) PCR protocol to measure absolute copy numbers of viral Tax DNA. Tax DNA was detectable in the tonsils in two NHPs, but to a greater extent in stomach in four NHPs. We also found Tax in parts of the small intestine, i.e. duodenum and Peyer's patches, in a NHP with high blood proviral load. Conclusion/Significance These data provide a quantitative analysis of STLV-1 Tax in the gastrointestinal tract and are, to our knowledge, the first indication of STLV-1 detection in stomach tissue of naturally infected asymptomatic NHPs. Although it is unclear how infection occurred - via from mother-to-child, sexual or via animal bites - our study suggests that these parts of the gastrointestinal tract might either serve as site of virus transmission or as viral reservoir.</jats:p>