"Infection of a novel host is the most frequent cause of fungal emerging disease" (Stukenbrock and McDonald, 2008; Giraud et al., 2010) Several examples from the literature of emerging infectious disease indicate that switches are often favored by changes in the encounter and not the compatibility filter (Woolhouse et al., 2005) . Ecological circumstances have exposed humans to a parasite they previously did not encounter. Such examples of host switches, particularly if the new host is distantly related to the original host, would seem to argue against the points made in the preceding sections regarding the importance of parasite accommodation to the idiosyncrasies of their host's immune system. If immunity is important in restricting parasite host ranges, how can such switches occur?