Mortality associated with renal and intestinal coccidiosis in juvenile eiders in Iceland.

The cause of unusual mortality observed in late June 1993 among hundreds of eider-ducklings (Somateria mollissima) originating from a colony of approximately 600 breeding eider ducks at Bildudalur, West-Iceland, was studied. The mortality occurred two weeks after a large-scale washing of gravel was initiated in a river-bed close to the colony. As a consequence marked environmental changes occurred in the area when a mud-layer gradually accumulated on the sea-bed around the colony. Necropsies, bacteriological, histoparasitological and pathological examinations were carried out on 14 ducklings. The ducklings were severely emaciated. Routine bacteriological tests performed were negative. Parasitological examinations revealed infection in some of the ducklings by an intestinal eimeriid of an unknown taxonomic status, and slight to moderate intestinal helminth infections. A prominent feature, observed in all ducklings, was greatly enlarged kidneys which were variegated with white or yellowish nodules. Kidney smears contained accumulations of urate crystals and huge numbers of the renal coccidian Eimeria somateriae. Acute renal failure, caused by E. somateriae, is assumed to be responsible for the death of the ducklings. The intestinal eimeriid, however, might also have contributed to some of the deaths as pathological examination of the intestines showed local destruction and necrosis of villi. Actually, the above mentioned environmental accident likely reduced markedly the availability of appropriate food and also reduced the hunting success of the ducklings in the area. Therefore, the ducklings in the fjord were presumably undernourished and in bad condition. It is suggested that the environmental accident promoted somehow the acute mortalities. A possible explanation is that the bad condition of the ducklings decreased the resistance to diseases like coccidiosis but other explanations should not be excluded.