ABSTRACT
Abstract. This chapter addresses disease agents in the broad sense, including viruses, bacteria, fungi, protozoan and helminth parasites, and biological toxins. Some of these agents are known to cause mortality in sea ducks, some are thought to be incidental ndings, and the signicance of others is yet poorly understood. Although the focus of the chapter is on free-living sea ducks, the study of disease in this taxonomic group has been relatively limited and examples from captive sea ducks and other wild waterfowl are used to illustrate the pathogenicity of certain diseases. Much of the early work in sea ducks consisted of anecdotal and descriptive reports of parasites, but it was soon recognized that diseases such as avian cholera, renal coccidiosis, and intestinal
infections with acanthocephalans were causes of mortality in wild populations. More recently, adenoviruses, reoviruses, and the newly emergent Welleet Bay virus, for example, also have been linked to die-offs of sea ducks. Declining populations of animals are particularly vulnerable to the threats posed by disease and it is important that we improve our understanding of the signicance of disease in sea ducks. To conclude, we offer our recommendations for future directions in this eld.
