Evolution in a chronic RNA virus infection: selection on HTLV-I tax protein differs between healthy carriers and patients with tropical spastic paraparesis

J Mol Evol. 1996 Apr;42(4):452-8. doi: 10.1007/BF02498639.


HTLV-I causes T-cell leukemia and tropical spastic paraparesis (TSP) in a minority of infected people, whereas the majority remain healthy. The virus differs little in sequence between isolates but has been shown to have a quasispecies structure. Using the Nei and Gojobori algorithm, we have shown that the proportion of nonsynonymous to synonymous changes in HTLV-I proviral tax gene sequences from healthy seropositive subjects (Dn/Ds = 0.9 to 1.3) is significantly higher than those from TSP patients (Dn/Ds = 0.3 to 0.6). Here we show that the distinction between healthy seropositives and TSP patients can only be seen with proviral tax sequences, but not with cDNA, the amino-terminal or carboxy-terminal half of tax, or the rex gene. The Dn/Ds ratio of proviral tax sequences was used to analyze two TSP patients with atypical features and to investigate the influence of cytotoxic T cells (CTL) on the viral quasispecies.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Evolution*
  • Carrier State / immunology
  • Carrier State / virology*
  • Chronic Disease
  • DNA, Complementary
  • Gene Products, rex / genetics
  • Gene Products, tax / genetics*
  • Genetic Variation
  • Genome, Viral
  • Human T-lymphotropic virus 1 / classification
  • Human T-lymphotropic virus 1 / genetics*
  • Humans
  • Paraparesis, Tropical Spastic / immunology
  • Paraparesis, Tropical Spastic / mortality
  • Paraparesis, Tropical Spastic / virology*
  • Selection, Genetic
  • T-Lymphocytes, Cytotoxic
  • Time Factors


  • DNA, Complementary
  • Gene Products, rex
  • Gene Products, tax