Sample collection.

Vervet monkeys were individually trapped by using established methods (24), the details of which were described previously (23). Briefly, each animal was trapped, sedated, and bled via venous puncture. During sampling, a detailed physical examination was performed, clinical signs were assessed, and the approximate age and sex of each individual were noted. Each vervet monkey sampled had a microchip implanted for further identification and for the prevention of duplicate sampling. Upon blood collection, plasma was purified and immediately stored at −80°C.