Isospora plectrophenaxia n. sp (Apicomplexa: Eimeriidae), a new coccidian parasite found in Snow Bunting (Plectrophenax nivalis) nestlings on Spitsbergen.

Faecal samples were collected from four 8 days old snow bunting nestlings from one nest in Ny-Alesund, Spitsbergen, in summer 2006. After sporulation, samples were examined for coccidian parasites using flotation centrifuging. We found isosporan oocysts in three birds, intensity of infection varied between individuals from 35 to 6,000 oocysts per defecation. All oocysts belonged to one species, which is described here as a new species. The spherical or subspherical oocysts (Fig. 1) have a brownish, smooth, relatively thin (about 1.1 microm) bilayered wall. Average size of sporulated oocysts was 26.2 +/- 0.13 x 23.6 +/- 0.16 microm (24.1-28.4 x 21.5-26.9; n = 10) with a shape index (length/width) of 1.11 +/- 0.01 (1.01-1.29). The sporulated oocysts have no micropyle or residuum but enclose one large (3.3 x 2.8 microm) ring-formed polar granule. The sporocysts are ovoidal, slightly pointed at the end opposite the Stieda body, 18.2 +/- 0.06 x 9.9 +/- 0.03 microm (17.1-19.0 x 9.0-10.8; n = 14), shape index 1.85 +/- 0.008 (1.70-1.99). The Stieda body has a prominent knob-like cap and a well-visible round substieda body. Sporocysts contain compact sporocyst residuum composed of small, uniform granules and sporozoits with usually three large refractile bodies and a smaller nucleus. The prepatent period is less than 8 days. This is the first description of an avian isosporan parasite that succeeds transmission while in the High Arctic.