Eschar in scrub typhus: clinical signature, immunopathogenesis, and diagnostic implications

SUMMARYScrub typhus, caused by Orientia tsutsugamushi, remains a major cause of acute undifferentiated febrile illness with an expanding global footprint. Early diagnosis is frequently delayed because of nonspecific systemic manifestations and geographic heterogeneity. The eschar, traditionally regarded as a characteristic but unreliable clinical sign, is better understood as a dynamic and biologically active lesion rather than a static cutaneous finding. Accumulating clinical, epidemiologic, and pathologic evidence demonstrates that eschar morphology and detectability vary widely with timing, anatomical location, host factors, and prior exposure, whereas its presence does not predict disease severity. Importantly, the eschar represents the primary site of pathogen inoculation, local amplification, and lymphatic dissemination preceding systemic endothelial infection. This biology has direct diagnostic implications: minimally invasive eschar swab-based molecular diagnostics consistently outperform blood-based assays during the early stages of illness and provide an optimal platform for emerging technologies. Furthermore, early eschar-based recognition dictates the timely initiation of targeted antimicrobial therapy, optimizing standard regimens and guiding safe treatment in vulnerable populations, while highlighting the need for novel therapeutics against drug-resistant strains. Reframing the eschar as a central clinical, diagnostic, and therapeutic axis offers a coherent framework for improving early recognition and future management strategies in scrub typhus.