Use of Eschar for the Molecular Diagnosis and Genotypic Characterisation of Orientia tsutsugamushi Causing Scrub Typhus

Scrub typhus caused by Orientia tsutsugamushi presents as an acute febrile illness with a varied presentation from mild illness to fatal disease in the absence of appropriate antibiotic treatment. Performing polymerase chain reaction (PCR) on eschar sample acts a rapid diagnostic tool in the early stage of scrub typhus when blood is negative. A total of eight patients from whom both whole blood and eschar samples were collected and tested by nested PCR targeting 56 kDa trichostatin A (TSA) gene to detect O. tsutsugamushi DNA. All (100%) eschar samples and three whole blood samples tested positive. Genetic analysis of the 56 kDa TSA gene sequences showed that the majority were related to Karp reference strains, while one clustered with Kawasaki strain. When present, eschar should be favoured as a diagnostic sample over whole blood in the early phase of infection.