Emergence of Infectious Diseases in
A. Alonso Aguirre
James A. House
Emerging diseases are defined as infections that either have newly appeared or have existed and are rapidly expanding their geographic range with a corresponding increase in detection, prevalence, mortality, or morbidity (Morse 1995). Many infectious diseases have been documented as emerging or reemerging in the marine environment (table 9.1). Specific factors responsible for the emergence of a new disease or the reemergence of an old disease can be identified in most cases. This chapter identifies the factors associated with emerging microbial infectious diseases of marine mammals.
An infectious disease may emerge in a population because of changes in the properties of the disease agent, changes in the host's resistance, environmental changes causing new interactions of the host and the disease agent, or simply the host being observed more carefully. We discuss the role of each element in recently recognized diseases of marine mammals.
Common microbial infectious disease agents of marine mammals are bacteria and viruses. Mycoplasmae, chlamydiae, fungi, prions, and other agents may contribute to an array of disease conditions but are not as well studied at this time and hence are not addressed in this chapter.
The ability of viruses or bacteria to cause disease may result from a change in the microorganism's genetic composition. This change can be categorized as a mutation (i.e., change in the nucleotide sequence) or as a reassortment/rearrangement of the nucleic acid within a segmented genome. Viable mutations are more