The Borneo wetlands teem with darting birds, slithering snakes and dangling orangutans. Blood-sucking leeches and slim, coiled microbes also abound. Some folks find out about these guys the hard way. Mary, 46, was a longtime marathon runner from Southern California. She was in my office at UCLA Medical Center for a checkup because she was training for a competition in Borneo, a rugged rainforest island in Southeast Asia. Along with 304 fellow athletes from 26 countries, the petite, fearless blon…