Mitochondrial genome characterization and phylogenetic position of a putative taeniid tapeworm (Taenia sp. QH-2023) isolated from Pseudois nayaur.

Pseudois nayaur (blue sheep), a second-class nationally protected species in China, inhabits the western regions of the country. During a cause-of-death investigation of P. nayaur, an unidentified cysticercus was discovered in the lung of a deceased P. nayaur. Using molecular and bioinformatics approaches, the mitochondrial (mt) genome and phylogenetic position of the parasite were characterized. The mt genome comprises 13,507 bp and encodes 12 protein-coding genes (PCGs), 22 tRNAs, and 2 rRNAs. Sequence analysis revealed a strong AT bias and codon usage preference typical of taeniid cestodes. These mitochondrial features may serve as valuable resources for molecular taxonomy and diagnostic marker development. Phylogenetic analyses based on complete mitochondrial genomes and cox1 sequences showed that the parasite clusters closely with Taenia regis and T. hydatigena. Based on sequence similarity and gene order collinearity, the parasite was tentatively designated as Taenia sp. QH-2023, with its PCGs exhibiting purifying selection consistent with other Taenia species. This study provides the first mt genome of a putative Taenia species infecting P. nayaur, providing useful reference data for future taxonomic, epidemiological, and conservation studies.