"Acute encephalitis syndrome in adults: Molecular and serological evidence of Orientia tsutsugamushi infection in Puducherry and neighboring districts of Tamil Nadu"

BACKGROUND: Scrub typhus has emerged as a prominent etiological agent of acute encephalitis syndrome (AES) in India. However, there is a dearth of information on its involvement in AES in South India. Knowing the specific etiology and its prevalence would help in the definitive management of patients, perhaps improving morbidity and mortality. METHODS: A cross-sectional descriptive study was performed in Pondicherry to determine the proportion of adult patients with Orientia tsutsugamushi infection causing AES between January 2020 and December 2021. Diagnosis was performed by a combination of a positive scrub IgM ELISA or a positive real-time PCR in CSF and/or blood sample. Phylogenetic analysis of O. tsutsugamushi isolates was performed to study variations in the 56-kDa type specific antigen (TSA) of O. tsutsugamushi. Seroprevalence of Orientia tsutsugamushi IgG antibodies was assessed using ELISA targeting 56KDa protein. RESULTS: Eleven percent of AES in adults was attributable to scrub typhus. The majority of sequences from the 19 isolates sequenced, according to phylogenetic analysis of 56-kDa proteins, resembled Karp- or Gilliam-like strains (63.1 % and 26.3 %, respectively). In Puducherry, O. tsutsugamushi IgG seropositivity was found to be 35 %. CONCLUSION: This study emphasized the importance of scrub typhus as the common etiology of AES in Puducherry, underscoring the need to integrate routine scrub typhus testing into AES diagnostic algorithm. Sequencing-based analysis of representative samples across the country helps to understand the diversity of O. tsutsugamushi.