HTLV-1 infection in japan, Hawaii, and California : the effect of immigration from endemic southwestern Japan

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Several studies have documented declining HTLV-1 seroprevalence among immigrants to non-endemic areas within one or two generations. we hypothesized a decrease in sexual transmission due to assimilation into the low-prevalence host population. and performed family studies of 22 Japanese-American (JA) HTLV-1+ women (cases) to a group of 80 Japanese (JN) HTLV-1+ women in Nagasaki (controls). The JA women were older than the JN women (median age 50 vs. 33) : JA women were enrolled from blood donor population, and JN women from postnatal care clinic. Educational level of JA women was higher than that of JN women. Antibody titers were slightly higher in the JA women (median 1/64 vs. 1/16), but the difference was not significant after adjustment for age. By the time of this report, the viral load analysis by PCR was done, waiting for computer analysis. Questionnaire data revealed that 75 (90%) of JN nad 20 (90%) of JA women had been breast-fed by their mothers, and both groups had similar duration of breast-feeding. There was no difference in HTLV-1 seroprevalence among current sexual partners of the JA women (2/11,18%) compared to partners of JN women (4/20,20%), Both groups had a median of 2 lifetime male sexual partners.Significantly (p<.05) more JN women than JA women reported that their current of previous sexual partner was from an endemic area (Kyushu, Shikoku or Okinawa) : 31/32 (97%) vs. 6/12 (50%). Condom usage was higher in the JN women, with 27 (33%) using a condom usually or always with their current partner, comared to only 3 (18%) of the 17 JA women with a current parther. We conclude that the immigration-related decline in HTLV-1 seroprevalence may be due to reduced sexual exposure of immigrant women to men from HTLV-1 endemic areas. Breast-feeding exposure was similar in endemic and immigrant women.