“…Owing to the low fidelity of lentivirus-encoded reverse transcriptase (RT), genomic mutation occurs frequently during reverse transcription of viral RNA to proviral DNA (Montelaro, 1992). Further attempts to isolate FIV strains have been carried out worldwide, and comparison of nucleotide sequences of isolates has revealed that genomic heterogeneity occurs among various FIV strains isolated in the U.S.A. (Talbott et aL, 1989;Olmsted et al, 1989b;Phillips et al, 1990), Switzerland (Morikawa et al, 1991), the Netherlands (Siebelink et al, 1992), Italy (Rigby et al, 1993), Australia (Greene et aL, 1993a, b) and Japan (Maki et al, 1992;Miyazawa et al, 1991). These reports also noted a high diversity of biological properties including antigenicity, cell tropism and replication kinetics.…”