Christopher Post was not yet home when he noticed the crimson spot, roughly nickel-sized, on his left biceps. Returning from the trip of a lifetime, a monthlong safari in Africa, he was tired, achy, and hot. Maybe it's eczema, the 50-year-old stockbroker reasoned. He'd be better in a couple of days.
But a few days later, Mr. Post was worse, with a higher fever. The spot on his arm was bigger. His internist was out of town, so he drove to a nearby hospital.
"Did you use malaria pills in Africa?" asked the emergency-room physician.
