Molecular epidemiology of human T lymphotropic virus type 1 transmission in Okinawa, Japan.

To clarify the route of human T lymphotropic virus type 1 (HTLV-1) transmission, we sequenced three proviral genome regions (gag, env, int) of HTLV-1 from 18 carriers in 7 families in Okinawa, Japan and compared the strains with isolates from other countries. The nucleotide substitution frequency among sequences derived from a single carrier was low; 0-0.24% in gag, 0-0.54% in env, and 0-0.34% in int. All sequences showed the closest identity to the Cosmopolitan strain, with differences of only 0-1.91%. All 8 mother/child pairs had identical nucleotide sequences. Of 3 pairs of spouses, 2 had identical sequences, with transmission probably from husband to wife. The mothers of both wives were HTLV-1-negative. The HTLV-1 sequence of the other wife showed three nucleotide differences from the sequence of her husband, but was identical to the sequence of her mother. These results support previous seroepidemiological studies that HTLV-1 transmission occurs from mother to children and also between spouses.