This volume focuses on those instances when benign and even beneficial relationships between microbes and their hosts opportunistically change and become detrimental toward the host.  It examines the triggering events which can factor into these changes, such as reduction in the hosts capacity for mounting an effective defensive response due to nutritional deprivation, coinfections and seemingly subtle environmental influences like the amounts of sunlight, temperature, and either water or air quality.  The effects of environmental changes can be compounded when they necessitate a physical relocation of species, in turn changing the probability of encounter between microbe and host.  The change also can result when pathogens, including virus species, either have modified the opportunist or attacked the hosts protective natural microflora.  The authors discuss these opportunistic interactions and assess their outcomes in both aquatic as well as terrestrial ecosystems, highlighting the impact on plant, invertebrate and vertebrate hosts.

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.