A Clinical Case of Scrub Typhus in the United States Forces Korea Patient with Eschar and Genetic Identification of Orientia tsutsugamushi Using Multiplex PCR-Based Next-Generation Sequencing

Utility of next-generation sequencing for the etiological diagnosis of Orientia tsutsugamushi infection

Background

Scrub typhus, an acute febrile disease caused by Orientia tsutsugamushi, is transmitted to humans through infected chigger mites. We present a case of scrub typhus in a previously healthy man from Shandong Province diagnosed using next-generation sequencing (NGS) and PCR and review recent literature on NGS for scrub typhus diagnosis.

Methods

NGS was utilized for testing whole blood collected on admission. Confirmatory testing was done by detecting IgM and IgG antibodies to Orientia in acute and convalescent sera by ELISA. Orientia 47-kDa protein gene TaqMan and standard PCR of the 56-kDa protein gene and Sanger sequencing were performed on eschar scab DNA.

Results

The NGS diagnosis was confirmed by 47-kDa protein gene TaqMan and sequencing of a fragment of the O. tsutsugamushi 56-kDa protein gene from the eschar scab. Analysis of this sequence and the NGS data indicated O. tsutsugamushi strain Cheeloo2020 is a novel genotype. Mapping of the NGS data against the O. tsutsugamushi Gilliam strain genome sequence identified 304 reads with high similarity.

Conclusions

NGS is not only useful for multiplex diagnosis of scrub typhus, but also provides insight into the genetic diversity of O. tsutsugamushi. The common failure to submit sequences to databases makes it difficult to determine the minimal quantity and quality of NGS data being used for the positive identification of Orientia DNA in clinical specimens.

Incidence of Scrub Typhus according to Changes in Geographic and Demographic Characteristic in the Chungcheong Region of Korea

To ascertain the incidence trends of scrub typhus in the Chungcheong region, we analyzed the epidemiological survey information of 14,379 cases of scrub typhus reported to the integrated disease health management system of the Korea Centers for Disease Control and Prevention between 2012 and 2022, along with demographic data from the Korean Statistics Information Service. Geographical analyses were performed to confirm the correlation between high-risk areas and the proportion of elderly people. The average age, proportion of elderly people, and changes in the agricultural population were statistically associated with incidence. The incidence of scrub typhus, and the agricultural population, in the Chungcheong region has decreased compared with that in 2012-2013. However, recent trends indicate a resurgence linked to increased outdoor activity, with higher risks observed in older age groups. Additionally, advancing age correlates with a heightened probability of reinfection and additional infections with other febrile diseases. The incidence of scrub typhus in the Chungcheong region (2012-2022) is changing according to age and route of infection, highlighting the need for revised prevention and promotion policies.