[1] Univ Pittsburgh, Reg Biocontainment Lab, Ctr Vaccine Res, Pittsburgh, PA 15261 USA
[2] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Infect Dis & Microbiol, Pittsburgh, PA 15261 USA
[3] Ctr Dis Control & Prevent, Special Pathogens Branch, Div Viral & Rickettsial Dis, Atlanta, GA 30333 USA