^aTulane National Primate Research Center, Covington, Louisiana 70433, USA

^bDepartment of Tropical Medicine, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana 70112, USA

^cMedical Research Station, Kumba, Cameroon, USA

^dTheoretical Biology and Biophysics, Group T-10, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

^eAlbert Einstein College of Medicine, Bronx, New York, USA.

Received 10 November, 2005

Revised 2 February, 2006

Accepted 24 February, 2006

Sponsorship: This work was supported by funds from grant RO1 AI-44596.