Multiclade HIV-1 Infection in Japan

             Unlike several countries in Asia and Southeast Asia, Japan has not experienced an explosive increase in cases of HIV-1 infection and AIDS.  However, a definite upward trend has been noted, as evidenced by the record number of 250 AIDS cases recorded in 1997.  Moreover, given the circulation of multiple HIV-1 subtypes in the region and the sizable inward and outward movement of foreign-born migrants and Japanese tourists, multiclade HIV-1 infection is presumably occurring in Japan.  To clarify recent trends in the molecular epidemiology of HIV-1 infection in Japan, we analyzed HIV-1 env gene sequences in 27 infected individuals.  Banked plasma samples from 27 randomly selected individuals, attending an HIV-1 outpatient clinic at the Nagoya National Hospital between June 1994 to August 1997, were analyzed for a 273-nucleotide region spanning the V3 loop of the gp120-encoding HIV-1 env gene by reverse transcription-polymerase chain reaction.  Of the 27 study participants, 16 were infected by heterosexual sex, six by homosexual sex and five by transfusion of blood products.  All 11 individuals infected through homosexual sex or blood transfusion were Japanese; of the 16 infected through high-risk heterosexual sex, seven were Japanese and nine were foreign-born immigrants (four Thai, three Brazilian, one Ethiopian and one Indian).

             All individuals infected through transfusion of HIV-1-contaminated blood products were hemophiliac men infected in Japan. Accurate dating of their infection could be made to 1984-85. By contrast, the date and place of acquiring HIV-1 infection among heterosexually and homosexually infected individuals were difficult to ascertain in all but a few cases, largely because these individuals had sexual contact with multiple partners in Japan and abroad.  Male-to-male sex accounted for infection in six men (all Japanese), three of whom were infected in Japan.  High-risk heterosexual sex was the mode of HIV-1 infection in seven women (two Japanese and five non-Japanese) and nine men (five Japanese and four non-Japanese).  Nearly all heterosexually infected men admitted to having unprotected sexual intercourse with commercial sex workers either in Japan or in their home country.  Among heterosexually infected individuals, sequence and phylogenetic analyses indicated HIV-1 subtype C in an immigrant Ethiopian woman and an Indian man, subtype E in three Thai immigrants and two Japanese men, and subtype Bâ in a Japanese man and his Thai wife.  The remaining seven heterosexually infected patients, as well as the 11 individuals infected by homosexual sex or blood transfusion, were infected with subtype B.  Heterosexual and homosexual transmission of HIV-1 now account for virtually all new infections in Japan.  The presence of multiple HIV-1 subtypes among heterosexually infected men and women in Japan underscores the need for heightened prevention campaigns, particularly targeting men engaging in unprotected vaginal intercourse with high-risk partners.  

Nishiura, Y., Nerurkar, V.R., Utsumi, M., Mukai, E., Dashwood, W-M., Ieong, M-C., and Yanagihara, R.:  Multiclade HIV-1 infection in Japan:  Genetic and phylogenetic analyses of virus strains among homosexuals and heterosexuals. International Journal of Infectious Diseases  (in preparation).

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