[1] Harvard Univ, New England Reg Primate Res Ctr, Sch Med, Dept Microbiol & Mol Genet, Southborough, MA 01772 USA
[2] Free Univ Berlin, Dept Biol, D-14195 Berlin, Germany
[3] USA, Med Res Inst Infect Dis, Frederick, MD 21702 USA
[4] Ctr Dis Control & Prevent, Natl Ctr Infect Dis, Special Pathogens Branch, Atlanta, GA 30332 USA
[5] Harvard Univ, Sch Med, Childrens Hosp, Dept Pediat, Boston, MA 02115 USA