How well do surrogate hosts serve as model systems for understanding pathogenicity.- Host-symbiont relationships: understanding the change from guest to pest.- Opportunistic infections in elasmobranchs.- Bacterial opportunistic pathogens of fish.- Fungal secondary invaders of fish.- Opportunistic pathogens of marine mammals.- Opportunistic pathogens of terrestrial plants.- Non-spore-forming bacterial entomopathogens – their toxins, hosts and the environment: why be a pathogen.- Opportunistic infections of avians.- Opportunistic algae, fungi, and ichthyosporea associated with mammalian livestock disease.- Opportunisitic pathogens of humans.