[1] Univ Texas Med Branch, Galveston Natl Lab, Galveston, TX 77550 USA
[2] Univ Texas Med Branch, Dept Microbiol & Immunol, Galveston, TX 77550 USA
[3] NIAID, Virol Lab, Div Intramural Res, NIH,Rocky Mt Labs, Hamilton, MT USA
[4] Publ Hlth Agcy Canada, Natl Microbiol Lab, Winnipeg, MB, Canada
[5] Univ Manitoba, Dept Med Microbiol, Winnipeg, MB, Canada