Diseases and Parasites of Birds: Ecology and Epidemiology in a Changing World

Parasites, the diseases they cause, and their hosts together share a complex evolutionary history. In recent years, however, long-term host-parasite-disease associations have been disrupted primarily due to profound anthropogenic changes in the environment and emerging and re-emerging infectious diseases are recognized as important ecological forces. Birds serve as excellent models in the study of the ecology of parasites and diseases. In this study, I evaluated three aspects of avian disease dynamics. First, I reviewed the role of birds in the spread of highly pathogenic avian influenza (HPAI) of the subtype H5N1 from southeastern Asia. Although limited cases of HPAI have been recorded in wild birds, the overwhelming route of movement and geographic spread of the virus has been via poultry trade and related operations, contrary to scientific and media speculation. The role of wild birds in maintaining the disease in the wild remains unknown and requires considerable study. Control of poultry and human-wildlife-domestic animal interfaces needs to be strengthened to prevent the mixing, mutation and spread of such viruses. -- Second, I evaluated the ecology of the Lyme disease spirochete, Borrelia garinii, in seabirds from eastern Canadian colonies. I record the first case of B. garinii from Gull Island, Newfoundland. Movement of this spirochete is consistent with short-distance movements of seabirds and the presence of the seabird tick, Ixodes uriae, the vector of the spirochete. Identical strains occurring on both hemispheres have suggested long distance movement of the spirochete, however, current information does not offer a good explanation for trans-hemispheric exchange. The strains obtained from Gull Island were similar to eastern European strains, consistent with a hypothesized invasion of colonies in the North Sea from mainland Europe followed by a gradual northwestern movement, with seabirds dispersing into Northwest Atlantic seabird colonies. The timing of breeding of the host seabirds and the life cycle of Ixodes uriae are both very important, complex factors influencing the widespread distribution of B. garinii in the northern hemisphere. -- Third, I examined changes in the endoparasite fauna of common (Uria aalge) and Thick-billed Murres (Li. lomvia) since the late sixties in the Northwest Atlantic. Species composition and relative abundance were very different in both species reflecting long-term change in the marine environment. I recorded the first case of Alcataenia longicervica, a tapeworm species endemic to the North Pacific basin, from murres in Newfoundland. The presence of this species in varying abundance in Coats Island, the Gannet Islands, Gull Island and Greenland reflects a possible route of invasion along the Siberian, Kara and Laptev seas with infected intermediate hosts (euphausiids). Changes in distributions of these tapeworms in murres therefore reflect long-term change in the distribution, abundance and intermingling of Arctic, Pacific and Atlantic krill.

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