Southern African Origin of HTLV-1 in Romania

Abstract

In Europe, most HTLV-1-infected individuals originate from highly endemic regions such as West Indies, sub-Saharan Africa, and South America. The only genuine endemic region for HTLV-1 in Europe is Romania where ATL series have been reported among Romanian patients. Our objective is to better understand the origin of this endemic focus based on a study of the genetic diversity of HTLV-1 in Romanians. DNA was obtained from PBMCs/buffy coats of 11 unrelated HTLV-1-infected individuals of Romanian origin. They include 9 ATL cases and 2 asymptomatic carriers. LTR sequences were obtained for all specimens. Complete genomic HTLV-1 sequences were obtained using four PCR series on 10 specimens. Phylogenetic trees were generated from multiple alignments using HTLV-1 prototypic sequences and the new generated sequences. Most of the complete LTR sequences (756-bp) showed low nucleotide diversity, ranging from 0% to 0.8% difference, and were closely related (less than 0.8% divergence) to the only previously characterized Romanian strain, RKI2. One strain, ROU7, diverged slightly (1.5% on average) from the others. Phylogenetic analyses both on partial LTR and the complete genome demonstrate that the 11 sequences belong to the HTLV-1a cosmopolitan genotype and 10 of them belong to the previously denominated a-TC Mozambique-Southern Africa A subgroup. In this study, we demonstrated that the HTLV-1 present in Romania most probably originated in Southern Africa. As most Romanian HTLV-1 strains are very closely related, we can assume that HTLV-1 has been introduced into the Romanian population recently. Further studies are ongoing to decipher the routes of arrival and dissemination of these HTLV-1 strains, and to date the emergence of this endemic focus in Central Europe.

Fig 1. Phylogenetic tree generated with neighbor-joining (NJ) method on a 485-bp fragment of the LTR region for 81 HTLV-1 available sequences including the 11 generated in this work (in bold red type).

The numbers at some nodes of the tree correspond to the probability of each monophyletic groupe (a-LRT). The branch lengths are drawn to scale with bar indicating 0.005-nucleotide replacement by site. The ATK-1 and ATL-25 strains were used as outgroup.

Fig 2. Phylogenetic tree generated with neighbor-joining (NJ) method on a 6,366-bp fragment of the HTLV-1 Gag-Pol-Env-Tax concatenated genes for 56 available sequences including the 10 generated in this work (in bold red type).

The numbers at some nodes of the tree correspond to the probability of each monophyletic groupe (a-LRT). The branch lengths are drawn to scale with bar indicating 0.01-nucleotide replacement by site. Five HTLV-1c Australo-Melanesian strains were used as outgroup.