Tsutsugamushi disease, also known as scrub typhus, is transmitted by chiggers. Humans typically contract this acute infectious disease through bites (Tamura et al., 1995). It was previously believed to only involve one species, O. tsutsugamushi, and was confined to the area designated as the “tsutsugamushi triangle”, which extends from Afghanistan through China and Korea, covering the western Pacific and Indian Ocean islands, and reaching northern Australia. Around one billion individuals face the risk of scrub typhus (Kelly et al., 2009), with approximately one million cases reported each year (Watt and Parola, 2003; Hu et al., 2015). However, recently, cases have been reported in several regions of South America and Chile, where a new pathogen, cand. O. chiloensis, has been discovered (Abarca et al., 2020; Jiang et al., 2022). Additionally, pathogens such as cand. O.chuto have been found in the United Arab Emirates and Kenya (Izzard et al., 2010; Masakhwe et al., 2018). This indicates that the risk of scrub typhus caused by different species of Orientia is broader and more significant than previously known, potentially having global implications.

Before 1986, reports and outbreaks of scrub typhus cases were mainly concentrated in regions south of the Changjiang River in China (Yu, 1997). Subsequently, the epidemic continuously spread and expanded to northern regions of the country. In the north, strains with lower virulence such as Gilliam, Kawasaki, and Yonchon genotypes, were predominated (Zhang et al., 2014). In 1997, the presence of scrub typhus was first reported in the Taihang Mountain area of Hebei Province (Chen et al., 2000). However, due to Hebei being in a transitional endemic area with strains of lower virulence, there have been few documented cases and related investigation (Lu et al., 2018).

This study conducted laboratory diagnosis of a scrub typhus case in Shijiazhuang City, Hebei Province. Utilizing serological and molecular biology methods, we confirmed that the case was caused by the Kawasaki strain. This research aims to elucidate the genotype of O. tsutsugamushi in Hebei Province, provide theoretical basis and reference for clinical diagnosis.

Hebei Province is situated in the intermediary zone between the northern and southern endemic regions. The province showcases a variety of terrains, encompassing undulating hills, forests, and plains. Its Taihang Mountain area was designated as a natural focus of Scrub typhus as early as 1997, with the initial confirmed case of Scrub typhus in Hebei Province emerging from this locality (Zhang et al., 2013; Li et al., 2020). In 2018, Hebei Province confirmed its first case of Kawasaki disease caused by O. tsutsugamushi infection, located in Baoding City, Hebei Province (Lu et al., 2018). The genotype of this case matched that of cases in Shandong in 2013 and showed a certain trend of transmission (Li et al., 2013). Serving as the provincial capital of Hebei, Shijiazhuang falls under the category of a transitional endemic region, located in the central-southern part of the province characterized primarily by flat topography. The cityhas no documented Scrub typhus so far. This research presents a laboratory-confirmed case of Scrub typhus in Shijiazhuang, marking the city’s inaugural instance.

The case indicates that the patient has a history of outdoor exposure, presenting with a fever and a specific scab. Orientia spp. specific PCR methods targeted 56-kDa and groEL genes were positive and phylogenetic analysis showed the causative agent was closed to Kawasaki genotype. The Weil-Felix test shows OXk antibody titer above 1:80. Serum antibody testing shows positive IgG antibodies to O. tsutsugamushi in both acute and convalescent phase samples, with the IgG antibody titer in convalescent phase samples being four times higher than that in the acute phase. Consistent with the clinical diagnostic criteria for scrub typhus infection (Yang and Ren, 2012; Lu et al., 2023). These results indicate that the patient is suffering from scrub typhus.

Hospitals commonly rely on the Weil-Felix test for scrub typhus diagnosis due to its simplicity and ease of use, but it has limitations in sensitivity and specificity, leading to potential misdiagnosis (Sadanandane et al., 2018). Although IFA is considered the gold standard, its diagnostic value is hindered by subjectivity and antigen restrictions. In contrast, molecular biology techniques offer advantages in sensitivity, specificity, speed and simplicity, and are widely used in identifying and typing O. tsutsugamushi, the causative agent of scrub typhus.

O. tsutsugamushi infection exhibits diversity. Homology analysis of the 56-kDa antigen gene sequence indicates approximately nine genotypes: Karp, Kato, Gilliam, Kawasaki, Kuroki, Saitama, TA763, JG, and Shimokoshi (Kelly et al., 2009; Lu et al., 2010). Based on varying virulence in mice, strains are classified as highly virulent, moderately virulent, or weakly virulent, with Karp and Kato classified as highly virulent, Kawasaki and Kuroki as weakly virulent, and Gilliam exhibiting intermediate virulence. Gene sequencing and phylogenetic analysis revealed high similarity of the patient’s O. tsutsugamushi strain 56-kDa and groEL genes to the known Kawasaki genotype, providing strong evidence of infection with an O. tsutsugamushi Kawasaki genotype strain in this case.

This study identified a patient with a scab in Shijiazhuang City, Hebei Province. Through epidemiological investigation, clinical diagnosis, and laboratory testing, the patient was ultimately diagnosed with Scrub typhus infection. This represents the first laboratory confirmed case of Scrub typhus in Shijiazhuang City, filling a gap in reported cases and enriching the pathogen spectrum of O. tsutsugamushi infections in Hebei Province. This discovery provides important assistance for the diagnosis of scrub typhus in hospitals in the region and establishes clinical evidence. The report raises awareness among healthcare professionals about the presence of scrub typhus in Shijiazhuang City and contributes to the development of effective diagnostic and preventive measures.

The study is subject to limitations, primarily due to the inability to definitively determine the transmission route of the disease. Despite detailed analysis of the cases, the lack of sufficient data on vectors and host animals precludes the establishment of its transmission mechanism. Additionally, reliance solely on two gene segments for the identification of the spotted fever strain through genetic sequence analysis may introduce inherent limitations (Batty et al., 2018). Future research efforts could address these constraints through comprehensive epidemiological investigations and whole-genome sequencing, ensuring the comprehensiveness and accuracy of identification results.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/Supplementary material.

The studies involving humans were approved by the Ethics Committee of the First People’s Hospital of Shijiazhuang City (No. 201706). The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

HL: Conceptualization, Methodology, Writing – original draft, Writing – review and editing. JL: Methodology, Writing – original draft. RF: Writing – original draft. GH: Writing – original draft. MS: Writing – original draft. YL: Writing – review and editing.