Molecular characterisation of Sarcocystis rileyi from a common eider (Somateria mollissima) in Norway

The breast and leg muscles of a common eider (Somateria mollissima; Anatidae: Anseriformes) from northern Norway contained numerous grossly visible cigar-shaped sarcocysts measuring about 5 x 1 mm. Light microscopic examination of isolated sarcocysts revealed that they were encapsulated by a thin fibrous layer, underneath which there was a thin and fairly smooth cyst wall with no visible protrusions. The cystozoites were straight, spindle-shaped and about 13 mu m long. Genomic DNA was extracted from 12 excised sarcocysts and each DNA isolate was subjected to PCR amplification of one to four loci: the 18S and 28S ribosomal RNA genes (four isolates), the internal transcribed spacer 1 (ITS1) region (six isolates) and the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) (12 isolates). At the three nuclear loci, the new sequences showed 99.9-100 % sequence identity with previous sequences of Sarcocystis rileyi from the mallard duck in Lithuania and USA, and they could therefore be assigned to this species. At cox1, the new sequences of S. rileyi were most similar to Sarcocystis arctica and Sarcocystis neurona, but the most closely related Sarcocystis spp. in birds have not been sequenced at this locus. There was no sequence variation at any locus between the 4-12 examined isolates of S. rileyi. This is the first genetically verified record of S. rileyi in the common eider, as well as in any bird species in Norway. The phylogenetic placement of S. rileyi was inferred separately from 28S rRNA gene and cox1 sequences, and similar results were obtained in both analyses.