[1] Univ Maryland, Sch Med, Ctr Vaccine Dev, Baltimore, MD 21201 USA
[2] Univ Maryland, Sch Med, Dept Med, Div Geog Med, Baltimore, MD 21201 USA
[3] Univ Maryland, Sch Med, Dept Pediat, Div Infect Dis & Trop Pediat, Baltimore, MD 21201 USA
[4] Univ Maryland, Sch Med, Dept Microbiol & Immunol, Baltimore, MD 21201 USA