Description of Sarcocystis turdusi sp nov from the common blackbird (Turdus merula)

Cysts of Sarcocystis species were found in 24 of 44 (54.5%) examined blackbirds (Turdus merula). Under the light microscope, only 1 morphological type of cyst was found in all birds investigated. Ribbon-shaped cysts were long (the largest fragment found amounted to 7 mm) and of different thickness (25-206 mu m). A cyst wall reached up to 3.5 mu m and had finger-like protrusions. Under the transmission electron microscope, a single cyst isolated from 1 blackbird was studied. The cyst wall was 2.5-4.4 mu m thick, had club- or irregularly-shaped and sometimes branched protrusions that differed in size. The content of cysts was divided into large chambers by septa. Orange segment-shaped cystozoites were 6.2x1.4 (5.5-7.2x1.2-1.5) mu m. This type of cyst wall has never been described in Sarcocystis species isolated from birds, thus far. The results of 18S rDNA, 28S rDNA and ITS-1 region sequences showed that S. turdusi was most closely related to S. columbae, S. calchasi, S. wobeseri, S. cornixi and Sarcocystis sp. ex Accipiter nisus parasitizing birds. Phylogenetic results suggest that predatory birds are the most probable definitive hosts of S. turdusi.