This is an observational study of patients with scrub typhus (rapid diagnostic test/quantitative polymerase chain reaction (RDT/qPCR) positive) and an inoculation eschar present on examination, recruited from Chiangrai Prachanukroh Hospital, North of Thailand.

In this study, we aim to:

• Investigate relevant pathogen dissemination dynamics, early innate immune response, and pathogen-host interactions in scrub typhus using a minimal set of easily accessible samples; the inoculation eschar (crust or biopsy), whole blood and - where possible - a lymph node fine-needle aspiration (FNA).
• Determine the potential use of the inoculation eschar for improving early diagnostics and assessing the diversity of human pathogenic strains; by evaluating non-invasive swabs and scrapings, as well as biopsies for molecular diagnostics templates.
• Dissect the underlying patho-biology associated with the inoculation eschar and in a subgroup, including the draining lymph node; by defining the spectrum of infected cells via microscopy and double-immune labeling; by determining cytokine and RNA gene expression profiles in blood peripheral blood mononuclear cell (PBMCs) and eschar samples.

Data sharing:

No future analysis or study of legacy data/specimens including data sharing for purposes not specified in the protocol will be done without seeking further regulatory (EC/IRB) approval

• Any requests for data sharing will be considered by MORU's data sharing committee
• Any data subsequently shared will be anonymised and will not include personal identifiers

Scrub typhus patients will be recruited into the scrub typhus patient (EXP) arm of the study. There will be 3 sub-groups:

• EXPa (n=12) will have blood and non-invasive eschar samples collected (consent to study, declined biopsy).
• EXPb (n=12) will have blood, non-invasive eschar samples, and an eschar biopsy collected (consent to study, draining lymph node (LN) inaccessible).
• EXPc (n=12) will have blood, non-invasive eschar samples, eschar biopsy, and LN FNA collected (consent to study, draining LN accessible).

Samples will be collected at baseline (all) and 2 weeks (blood only).

Control participants will be recruited into the scrub typhus control.

- EXC (n=12) are healthy individuals, attending hospital for elective/minor surgery or treatment of minor skin injury, and normally reside in a scrub typhus endemic region. Blood and a skin sample will be collected at baseline only.

Scrub Typhus Patients (EXP) inclusion criteria:

• Age ≥7 years old.
• Presentation to hospital with fever in ≤14 days and a clinical suspicion of typhus.
• Eschar observed on examination.
• Scrub typhus RDT positive or OT qPCR positive (if qPCR available at local site by time of study initiation).
• Willingness to participate in the study. Written informed consent obtained from the patient (≥18 years old) or, written informed assent from participant (≥7 to <18years old) along with written informed consent from participant's parent(s)/legal guardian(s).

Scrub Typhus Controls (EXC) inclusion criteria:

• Age ≥7 years old.
• Clinically well, attending elective/minor surgery or for treatment of minor skin injury.
• Historical diagnosis of scrub typhus (RDT, serology, and/or PCR positivity) more than 2 years ago or living in an endemic area with high risk of previous exposure.
• Willingness to participate in the study. Written informed consent obtained from the patient (≥18 years old) or written informed assent from participant (≥7 to <18years old) along with written informed consent from participant's parent(s)/legal guardian(s).

Scrub Typhus Patients (EXP) exclusion criteria:

• Current TB or TB treatment in ≤6 months (contains OT-effective antimicrobials)
• Documented HIV infection, use of steroids, chemotherapy, other immunosuppressants, or herbal remedies containing steroids, and/or pregnancy

Scrub Typhus Controls (EXC) exclusion criteria:

• Significant acute intercurrent illness at the time of admission including fever >37.5˚C or infection (including TB) requiring antibiotics
• Documented HIV infection, use of steroids, chemotherapy, other immunosuppressants, or herbal remedies containing steroids, and/or pregnancy

EXP: Male and female patients ≥7 years old with confirmed acute scrub typhus and an eschar present on examination (N=36).

EXC: Healthy individuals ≥7 years old who normally reside in a scrub typhus endemic region, attending hospital for elective/minor surgery or treatment of minor skin injury, and preferably age and sex-matched (N=12).