The sika deer (Cervus nippon) is one of the most common species of wildlife in Japan. This study aimed to reveal the prevalence of tick-borne protozoan parasites in wild sika deer living in western Japan. We used nested polymerase chain reaction (PCR) to detect the 18S rRNA gene of tick-borne apicomplexan parasites (Babesia, Theileria, and Hepatozoon spp.) from 276 blood and liver samples from sika deer captured in the Yamaguchi, Oita, Kagoshima, Okayama, Ehime, Kochi, and Tokushima Prefectures. In total, 259 samples (259/276; 93.8%) tested positive in the nested PCR screening. Gene sequencing revealed that 99.6% (258/259) of positive samples contained Theileria sp. (sika 1), while Theileria sp. (sika 2), another Theileria species, was detected in only 3 samples. We also found that one sample from a sika deer captured in Kagoshima contained the gene of an unidentified Babesia sp. related to Babesia sp. Kh-Hj42, which was previously collected from tick in western Siberia. In conclusion, we found a high prevalence of piroplasms in sika deer from western Japan, and DNA analysis revealed that Theileria sp. (sika 1) had the highest infection rate.

梅花鹿（Cervus nippon）是日本最常见的野生动物之一。这项研究旨在揭示生活在日本西部的野生梅花鹿中tick传播的原生动物寄生虫的患病率。我们使用巢式聚合酶链式反应（PCR）来检测蜱传顶复门寄生虫（的18S rRNA基因巴贝斯虫，泰勒虫，和Hepatozoon从梅花鹿276个血液和肝脏样品中的山口，大分，鹿儿岛，冈山捕获spp。）的，爱媛，高知和德岛县。总共有259个样本（259/276; 93.8％）在巢式PCR筛选中呈阳性。基因测序发现，阳性样品的99.6％（259分之258）含有泰勒属。（sika 1），而泰勒里亚sp。（Sika 2），另一种泰勒菌属，仅在3个样品中被检测到。我们还发现，从鹿儿岛捕获的梅花鹿的一个样本中包含一个身份不明的巴贝斯虫sp。的基因。与巴贝斯虫有关。Kh-Hj42，先前是从西伯利亚西部的tick中收集的。总之，我们在日本西部的梅花鹿中发现了较高的种质资源，DNA分析表明，泰勒虫属。（sika 1）的感染率最高。