The health ministry has confirmed a case in Japan last year of an uncommon type of HIV found primarily in western Africa, according to sources.
A research team under the Health, Labor and Welfare Ministry identified it as HIV-2, which is genetically different from the more common HIV-1.
The only other confirmed HIV-2 case in Japan was revealed in 1993. The more recent incidence was reported in October, and the infection was confirmed in the person's antibodies. It is the first time in Japan that a person's genes have been infected with HIV-2.
The team was concerned that testing systems not designed to detect HIV-2 would fail to diagnose an HIV infection and alerted the ministry to this fear.
Public health centers and medical institutions have already adopted diagnostic systems applicable to HIV-2, although new steps may be needed for virus tests conducted by the Japan Red Cross on donated blood.
The ministry said the dangers of overlooking donated blood infected with HIV-2 are low because cases of this kind are rare in Japan, while antibody tests prior the virus tests are responsive to the less common virus.
According to the Japan Red Cross, however, antibody tests may fail to diagnose HIV infection during the initial period after the virus enters the body.
The ministry said it will scrutinize infection conditions in Japan and consider further measures.
HIV-2 is believed to be weaker than HIV-1 in terms of its infection capability and disease potential. Detected mostly in western Africa thus far, it has also infected people in the United States, India, France and South Korea.
Both the 1993 and 2002 patients are of South Korean nationality. A national research institute in 1993 reported an HIV-2 case involving a Japanese patient, but the report was not confirmed.