High genetic stability of TM1 and TM2 strains of subtype B feline immunodeficiency virus in long-term infection.

To know the genetic changes of feline immunodeficiency virus (FIV) in long-term infection in cats, we inoculated three specific pathogen-free cats with FIV isolates and determined a partial env sequence covering the V3-V5 region. In 2 cats infected with subtype B strains TM1 and TM2, only one amino acid change in region V3 was observed at 9 years post infection (y.p.i.), and no nucleotide substitutions were observed between 9 and 10 y.p.i., indicating that these strains are genetically stable. On the other hand, in a cat infected with subtype A strain Petaluma at 8.7 y.p.i., 3 nucleotide insertions (one amino acid insertion) in region V5, and 1 synonymous nucleotide substitution and 2 non-synonymous nucleotide substitutions in region V5, were observed.