Prevalence and molecular detection of Theileria in ixodid ticks in central and southern Shanxi, China

Theileria, an obligate intracellular parasitic protozoan transmitted primarily by ixodid ticks, poses a significant threat to animal health and livestock productivity. This study conducted a comprehensive investigation into the prevalence and genetic diversity of Theileria species in ixodid ticks in central and southern Shanxi Province, China.

First, a certain number of tick samples were collected, including 102 sheep-infesting ticks from Baitupo Village and Wangjiazhuang Village in Yangquan City, Shanxi Province, China, and a total of 60 cattle-infesting ticks from Daxigou Village in Yuncheng City and Matian Town in Jinzhong City, Shanxi Province. Then, genomic DNA was extracted from tick samples, followed by conventional PCR targeting a fragment of the 18S rRNA gene for the detection of Theileria. All positive amplicons were subsequently sent for Sanger sequencing. The obtained nucleotide sequences were subjected to phylogenetic analysis along with reference sequences retrieved from NCBI GenBank using MEGA-X software. DnaSP, Arlequin and PopART software were employed to conduct haplotype-based geographical evolution analysis for the same species of Theileria.

Molecular screening revealed an overall average Theileria infection prevalence of 67.28% (109/162) across the surveyed samples. The positive rates varied markedly by sampling site: 77.42% (48/62) in Baitupo Village, 47.50% (19/40) in Wangjiazhuang Village, 61.90% (13/21) in Daxigou Village, and 74.36% (29/39) in Matian Town. The infection rates of Theileria showed statistically significant differences among different regions (χ ² = 9.497, P = 0.023). Among these, forty sequences from positive sheep-infesting ticks for Theileria infection were identified as Theileria luwenshuni. The 11 sequences from positive cattle-infesting ticks were classified as Theileria orientalis. Phylogenetic analysis displayed that sequences of T. luwenshuni had the closest genetic relationship with strains previously identified in Changzhi, Shanxi, China (GenBank: OR999605). Meanwhile, T. orientalis sequences clustered together with the Chinese T. orientalis reference strain (GenBank: OQ507242.1). The phylogeographic analysis revealed that all T. luwenshuni isolates examined in this study belonged to a single conserved haplotype, while six divergent haplotypes were identified among T. orientalis sequences.

Our study revealed a high prevalence of Theileria infection among ixodid ticks in central and southern Shanxi, China, underscoring an urgent demand for targeted intervention strategies to limit the transmission of theileriosis and alleviate its rising risks to veterinary and public health.