Chen Li, Kong Yi-Chen, Tian Jia-Wei, Han Pei-Yu, Wu Song, He Chen-Jie, Ren Ti-Lian, Wang Bo, Qin Lian, Zhang Yun-Zhi
Institute of Preventive Medicine, School of Public Health, Yunnan Key Laboratory of Screening and Research on Anti-Pathogenic Plant Resources from Western Yunnan, Yunnan University Key Laboratory of Zoonotic Disease Cross-Border Prevention and Quarantine, Dali University, Dali, China.
Department of Public health, The People's Hospital of Leshan, Leshan, China.
Vet Med Sci. 2025 Sep;11(5):e70573. doi: 10.1002/vms3.70573.
Scrub typhus, also known as Tsutsugamushi disease (TD), is an acute febrile illness that poses a significant public health threat to nearly one billion people in the Asia-Pacific region. The disease is caused by Orientia tsutsugamushi (OT) and is primarily transmitted through the bite of chigger mite larvae. Due to its nonspecific clinical manifestations, early diagnosis is challenging, often leading to misdiagnosis or untreated cases. Yunnan Province, located on China's border, reports the highest annual incidence of scrub typhus, highlighting the need to better understand OT infection in both human patients and small mammals in this region.
In this study, clinical data on scrub typhus cases in Xiangyun County People's Hospital were retrospectively collected. Nested polymerase chain reaction (PCR) and semi-nested PCR were used to amplify the 56-kDa type-specific antigen (TSA) from samples collected from 64 patients and 93 small mammals, representing six genera and nine species, in Xiangyun County, Yunnan Province, China. Complete sequences of the 56-kDa TSA for each genotype were obtained through primer-walking and subjected to evolutionary and recombination analyses.
A total of 377 scrub typhus cases were enrolled at Xiangyun County Hospital from July 2015 to November 2020. The detection rates of OT in patients and small mammals were 28.13% (18/64) and 13.98% (13/93), respectively. Nine full-length 56-kDa TSA genes were identified, comprising four distinct genotypes: Karp-like (n = 3), Kato-like (n = 3), Gilliam (n = 2), and TA763 (n = 1). Patients infected with the Karp-like exhibited significantly more severe clinical symptoms, and the Karp-like genotype of patients was relatively common in Xiangyun County of Yunnan Province. The Gilliam-like and Karp-like genotypes were detected in the infected small mammals, and Apodemus chevrieri is a dominant species in cultivated fields. Recombination analysis revealed genetic overlap among strains of similar or different genotypes, suggesting that genetic diversity may contribute to the increased incidence of scrub typhus.
At least four genotypes of OT were present among patients, and it was infected by OT that at least four species of infected small mammals in cultivated areas and at least three species of infected small mammals in residential areas from Xiangyun County, Yunnan Province. The diversity of OT genotypes and infected small mammals, which causes frequent genetic recombination, is the main reason for the adaptive selection due to the genetic evolution of OT.
恙虫病，又称丛林斑疹伤寒（TD），是一种急性发热性疾病，对亚太地区近10亿人构成重大公共卫生威胁。该疾病由恙虫病东方体（OT）引起，主要通过恙螨幼虫叮咬传播。由于其临床表现不具特异性，早期诊断具有挑战性，常导致误诊或漏诊病例。位于中国边境的云南省报告的恙虫病年发病率最高，这凸显了更好地了解该地区人类患者和小型哺乳动物中OT感染情况的必要性。
在本研究中，回顾性收集了祥云县人民医院恙虫病病例的临床数据。采用巢式聚合酶链反应（PCR）和半巢式PCR从中国云南省祥云县64例患者和93只小型哺乳动物（代表6个属9个物种）采集的样本中扩增56 kDa型特异性抗原（TSA）。通过引物步移获得每个基因型56 kDa TSA的完整序列，并进行进化和重组分析。
2015年7月至2020年11月，祥云县医院共收治了恙虫病患者377例。患者和小型哺乳动物中OT的检出率分别为28.13%（18/64）和13.98%（13/93）。鉴定出9个全长56 kDa TSA基因，包括4种不同基因型：类Karp型（n = 3）、类Kato型（n = 3）、Gilliam型（n = 2）和TA763型（n = 1）。感染类Karp型的患者临床症状明显更严重，且类Karp型基因型在云南省祥云县患者中相对常见。在受感染的小型哺乳动物中检测到类Gilliam型和类Karp型基因型，高山姬鼠是耕地中的优势物种。重组分析揭示了相似或不同基因型菌株之间的遗传重叠，表明遗传多样性可能导致恙虫病发病率上升。
云南省祥云县患者中至少存在4种OT基因型感染，且至少有4种小型哺乳动物在耕地区域、至少有3种小型哺乳动物在居民区受OT感染。OT基因型和受感染小型哺乳动物的多样性导致频繁的基因重组，是OT基因进化进行适应性选择的主要原因。
