Phylogenetic and immunological investigations of complete TSA56 ORF of Orientia tsutsugamushi present in acute encephalitis syndrome cases from eastern Uttar Pradesh, India

Abstract

Scrub typhus (ST) caused by Orientia tsutsugamushi (OT), has long been known to cause acute encephalitis syndrome (AES) and acute febrile illness (AFI). The immunodominant 56 kDa protein of OT, which is encoded by the 56 kDa gene (1600 bp encoding 516–541 amino acids) is a commonly studied antigen for genotype and serotype assignment. Previous studies from India have utilized partial type specific antigen (TSA) 56 kDa sequences for OT strain characterisation. On the other hand, understanding the antigenic diversity of current OT strains, is critical for developing specific diagnostic tests and vaccines against ST. As a result, the current study analyses antigenic variants using the entire TSA56 ORF of OT from AES cases. Phylogenetic investigation using complete TSA56 ORF sequences revealed Karp and Gilliam were the circulating predominant strains of OT. Furthermore, Immuno-informatical analysis demonstrated that the majority of high-binding affinity CD4 TCEs against the most prevalent Indian human leukocyte antigen alleles were present in the S-VDIII/IV and S-VDIV spacer regions of TSA56 ORF. TSA56 conserved spacer is crucial for OT immunological response investigations. Further, the pathophysiological effects of spacer domains in ST require further investigation. Furthermore, the characterization of the TSA56 spacer region of the OT from different parts of India is critical for developing region-specific ST diagnostic assays and vaccines. Supplementary Information The online version contains supplementary material available at 10.1007/s00203-023-03492-1.

CRISPR/Cas12a-Based Detection Platform for Early and Rapid Diagnosis of Scrub Typhus

“…We assume that the antibody titer was too low to reveal the infection by ELISA IgM, as the interval window between fever onset and sample collection was too short. On the contrary, the shorter interval between fever onset to sample collection was too favorable for molecular detection, i.e., nucleic acid-based detection of the target before the initiation of therapeutic interventions [26,53]. The LoCIST could precisely detect the presence of OT in clinical samples that were detected as negative by ELISA; hence, the platform demonstrated its ability to detect the target at the earliest.…”

“…The complete ORF of the 56 kDa gene was amplified using genomic DNA extracted from the Gilliam and Karp genotypes of OT using the primer reported earlier [26] (Figure S1). PCR amplification was carried out using a Phusion™ High-Fidelity DNA Polymerase (Thermofisher, Waltham, MA, USA).…”