Different population dynamics of human T cell lymphotropic virus type II in intravenous drug users compared with endemically infected tribes

Different population dynamics of human T cell lymphotropic virus type II in intravenous drug users compared with endemically infected tribes

^*Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium; and ^‡Department of Medical Microbiology, University College Dublin, Dublin 4, Ireland

Communicated by Manfred Eigen, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany (received for review January 6, 1999)

Abstract

The phylogeny of human T cell lymphotropic virus type II (HTLV-II) was investigated by using strains isolated from Amerindian and Pygmy tribes, in which the virus is maintained primarily through mother-to-child transmission via breast-feeding, and strains from intravenous drug users (IDUs), in which spread is mainly blood-borne via needle sharing. Molecular clock analysis showed that HTLV-II has two different evolutionary rates with the molecular clock for the virus in IDUs ticking 150–350 times faster than the one in endemically infected tribes: 2.7 × 10⁻⁴ compared with 1.71/7.31 × 10⁻⁷ nucleotide substitutions per site per year in the long terminal repeat region. This dramatic acceleration of the evolutionary rate seems to be related with the mode of transmission. Mathematical models showed the correlation of these two molecular clocks with an endemic spread of HTLV-II in infected tribes compared with the epidemic spread in IDUs. We also noted a sharp increase in the population size of the virus among IDUs during the last decades probably caused by the worldwide increase in intravenous drug use.

Footnotes

↵ † To whom reprint requests should be addressed at: Rega Institute for Medical Research, Minderbroedersstraat 10, B-3000 Leuven, Belgium. E-mail: marco.salemi{at}uz.kuleuven.ac.be.
Abbreviations:

HTLV-I or -II,

human T cell lymphotropic virus type I or II;

IDU,

intravenous drug users;

IDUIIend,

HTLV-II strains isolated from endemically infected populations;

IIidu,

HTLV-II strains isolated from intravenous drug users;

LTR,

long terminal repeat;

LTTP,

lineages-through-time plots;

UPGMA,

unweighted pair group method with arithmetic;

TNg,

Tamura–Nei model of nucleotide substitution with γ-distributed rates across sites