[1] Univ Missouri, Sch Med, Dept Internal Med, Columbia, MO 65212 USA
[2] Univ Missouri, Sch Med, Dept Mol Microbiol & Immunol, Columbia, MO 65212 USA
[3] Univ Missouri, Sch Med, Dept Pathol, Columbia, MO 65212 USA
[4] Dept Vet Affairs Med Ctr, Res Serv, Columbia, MO 65212 USA