“Sometimes nothing happens,” Epstein said. A leap is made but the microbe remains benign in its new host, as it was in the old one. (Simian foamy virus?) In other cases, the result is very severe disease for a limited number of people, after which the pathogen comes to a dead end. (Hendra, Ebola.) In still other cases, the pathogen achieves great and far-reaching success in its new host.
