[1] Colorado State Univ, Arthropod Borne & Infect Dis Lab, Dept Microbiol Immunol & Parasitol, Ft Collins, CO 80523 USA
[2] Colorado State Univ, Anim Reprod & Biotechnol Lab, Equine Ctr, Ft Collins, CO 80523 USA
[3] Univ Queensland, Dept Microbiol & Parasitol, St Lucia, Qld 4072, Australia
[4] Ctr Dis Control & Prevent, Div Vector Borne Infect Dis, Ft Collins, CO 80522 USA
[5] USAF, Off Surg Gen, Washington, DC 20332 USA