The match showed that their model, though still crude and approximate, might help predict and explain the course of other disease outbreaks. “Our major conclusion,” wrote Anderson and May,20 “is that a ‘well-balanced’ host-parasite association is not necessarily one in which the parasite does little harm to its host.” Their italics: not necessarily. On the contrary, it depends. It depends on the specifics of the linkage between transmission and virulence, they explained. It depends on ecology and evolution.
