[1] Natl Inst Commuicable Dis, AIDS Virus Res Unit, ZA-2131 Johannesburg, South Africa
[2] Univ Cape Town, Div Med Virol, ZA-7925 Cape Town, South Africa
[3] Innovir Inst, ZA-2047 Johannesburg, South Africa
[4] Univ Witwatersrand, Dept Virol, ZA-2193 Johannesburg, South Africa