Identification and genetic characterization of <italic>Sarcocystis arctica</italic> and <italic>Sarcocystis lutrae</italic> in red foxes (<italic>Vulpes vulpes</italic>) from Baltic States and Spain.

Background: Typically, carnivores serve as definitive hosts for <italic>Sarcocystis</italic> spp. parasites; currently, their role as intermediate hosts is being elucidated. The present study aimed to identify and molecularly characterize <italic>Sarcocystis</italic> cysts detected in striated muscle of red foxes from different populations in Latvia, Lithuania and Spain. Methods: Muscle samples from 411 red foxes (<italic>Vulpes vulpes</italic>) and 269 racoon dogs (<italic>Nyctereutes procyonoides</italic>) from Latvia, 41 red foxes from Lithuania and 22 red foxes from Spain were examined for the presence of <italic>Sarcocystis</italic> sarcocysts by light microscopy (LM). <italic>Sarcocystis</italic> spp. were identified by transmission electron microscopy (TEM) and molecular biology techniques. Results: <italic>Sarcocystis</italic> cysts were detected in 11/411 (2.7%) Latvian, 3/41 (7.3%) Lithuanian, and 6/22 (27.3%) Spanish red foxes, however, cysts were not observed in the muscles of racoon dogs. Based on LM, TEM, <italic>18S</italic> rDNA, <italic>28S</italic> rDNA, ITS1, <italic>cox</italic>1 and <italic>rpoB</italic> sequences, <italic>Sarcocystis arctica</italic> and <italic>Sarcocystis lutrae</italic> cysts were identified in red fox muscles from Latvia and Lithuania, whereas only <italic>S. arctica</italic> was detected in Spain. The <italic>18S</italic> rDNA, <italic>28S</italic> rDNA and ITS1 sequences from the 21 isolates of <italic>S. arctica</italic> from Latvia, Lithuania and Spain were identical. By contrast, two and four haplotypes were determined based on mtDNA <italic>cox</italic>1 and apicoplast <italic>rpoB</italic> sequences, respectively. Polymorphisms were not detected between the two isolates of <italic>S. lutrae</italic> from Latvia and Lithuania. Based on phylogenetic results, <italic>S. arctica</italic> and <italic>S. lutrae</italic> were most closely related to <italic>Sarcocystis</italic> spp. using predatory mammals as intermediate hosts and to <italic>Sarcocystis</italic> species with a bird-bird life-cycle. Conclusions: Based on current knowledge, the red fox and Arctic fox (<italic>Vulpes lagopus</italic>) could act as intermediate host for the same two <italic>Sarcocystis</italic> species. Molecular results suggest the existence of two genetic lineages of <italic>S. arctica</italic>, and such divergence relies on its geographical distribution but not on their intermediate host species. [ABSTRACT FROM AUTHOR]