[1] Inst Pasteur, Unite Epidemiol Virus Oncogenes, Paris, France
[2] Inst Pasteur, CNRS, URA 1960, Unite Immunol Mol Parasites, Paris, France
[3] Univ Gothenburg, Dept Clin Virol, Gothenburg, Sweden
[4] Univ Calif San Francisco, Dept Lab Med, San Francisco, CA 94143 USA
[5] Univ Calif San Francisco, Dept Med, San Francisco, CA USA
[6] Univ Calif San Francisco, Dept Epidemiol Biostat, San Francisco, CA 94143 USA