Avian Schistosome Biodiversity

The subclass Digenea, with more than 2,500 genera, and 18,000 species worldwide exemplifies one of the most spectacular radiations among metazoan parasites. Adult digenetic trematodes are obligate parasites in most vertebrates. Digeneans have a unique dependence on mollusks as first intermediate hosts in which they reproduce asexually thus immensely increasing the number of infective larvae, one of the most distinctive attributes enabling their success. Representatives of several phyla serve as second intermediate hosts. As a result, these parasites inhabit a number of phyla and have colonized nearly every organ in their hosts. One of the most distinctive, biologically intriguing and medically significant families of digeneans is the Schistosomatidae.

Schistosomes are significant pathogens of birds and mammals. They are primarily associated with freshwater habitats and are found in temperate and tropical regions of the world. Schistosomes are biologically fascinating due to such features as dioecy, sexual dimorphism and a two-host life cycle: bird or mammal and snail. Some species cause schistosomiasis, a chronic debilitating disease in humans and domestic animals. Because of their profound medical and veterinary importance, the systematics and diversity of the four genera and 25 species of mammalian schistosomes are relatively well known. In contrast, study of the six genera and 60 species of avian schistosomes has suffered due to lack of expertise and challenges applying traditional methods of study. Lack of a sound systematic framework has, until recently, greatly impeded our understanding of cercarial dermatitis (swimmer’s itch) caused by these organisms.