Molecular detection and population genetic diversity analysis of Theileria ovis in partial regions of Xinjiang, China

Ovine theileriosis is a disease caused by the genus Theileria (e.g., T. ovis, T. lestoquardi), preventing the sheep farming industry from developing, particularly in regions reliant on sheep for milk, meat, and associated economic benefits. However, there is limited information available on the epidemiological data and genetic diversity of T. ovis in Xinjiang. This study was conducted in May 2024 to investigate the molecular prevalence of T. ovis in sheep from five counties (Shaya, Wensu, Aketao, Keping, Awati) in Xinjiang. A total of 357 blood samples were screened for the presence of Theileria DNA through the amplification of the 18S rRNA gene using PCR, the genetic diversity among the chosen T. ovis sequences from geographical regions (including sequences in this study) was subsequently analyzed. BLAST analysis confirmed that the detected Theileria pathogen was T. ovis. Statistical results showed that the infection rate of T. ovis in sheep was 44.5 % (159/357). The highest infection rate was observed in Awati County, while the lowest was recorded in Shaya County. The prevalence exhibited significant variation among the sampling sites (χ² = 115.3, p < 0.05). To characterize the phylogenetic relationships within the detected Theileria populations, the sequenced T. ovis isolates were analyzed and found to be 96.6-99.8 % similar, showing a high degree of similarity to isolates from Turkey. Haplotype analysis further demonstrated that H1 constitutes the core haplotype (including sequences from Turkey, Iraq and Saudi Arabia), surrounded by derivative haplotype. To further investigate these haplotype distributions, population structure analysis revealed distinct genetic diversity patterns among groups, showing that genetic groups G1 and G4 had high haplotype diversity (Hd) but low nucleotide diversity (Pi), whereas G2 and G3 had low Hd and high Pi. In addition, Tajima's D＜0 in all four T. ovis populations. These biological and genetic indices suggest that these populations are possibly undergoing expansion. Our results suggest that the protozoan parasitizing local sheep is T. ovis. Moreover, the local population of T. ovis is as rich in genetic diversity and population expansion as other populations in different geographical locations.