Molecular Evidence of Ovine Theileriosis in Selected Areas of Qinghai Province

Ovine theileriosis is a tick-borne hemoparasitic disease caused by protozoan parasites of the genus <i>Theileria</i>, which poses a substantial threat to sheep and goats. The disease is prevalent in northwestern China, yet studies on the diversity of its pathogens in Qinghai Province remain limited. From 2014 to 2025, 1062 blood samples were collected from sheep in 11 counties of Qinghai Province, and the <i>Theileria</i> spp. were investigated by PCR targeting the <i>18S</i> rRNA gene. Genetic diversity analysis was performed to assess sequence variations and phylogenetic relationships. The results show that 424 samples tested positive for <i>Theileria</i> spp., with an overall infection rate of 39.92%, including <i>T. uilenbergi</i> 26.74%, <i>T. luwenshuni</i> 22.41%, <i>T. ovis</i> 18.17%, <i>T. capreoli</i> 0.56%, and <i>Theileria</i> sp. OT3 0.09%. The co-infection rate was 22.69%. Six haplotypes were detected in both <i>T. uilenbergi</i> and <i>T. ovis</i>, and fifteen in <i>T. luwenshuni</i>. Hap 1 was the dominant haplotype for all three species, with respective proportions of 73.08%, 77.06% and 82.17%. Phylogenetic analysis showed the strains were most closely related to those from Hunan, Turkey, Shaanxi, etc. These findings reveal a high diversity of <i>Theileria</i> species in Qinghai sheep, which provides crucial epidemiological insights into the transmission dynamics of ovine theileriosis in Qinghai and vital support for developing effective control strategies.