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ORIGINAL RESEARCH article

Front. Microbiol.

Sec. Infectious Agents and Disease

Volume 16 - 2025 | doi: 10.3389/fmicb.2025.1634394

This article is part of the Research TopicZoonotic Diseases: Epidemiology, Multi-omics, and Host-pathogen Interactions Vol IIView all 5 articles

A Longitudinal Molecular Surveillance of Genetic heterogeneity of Orientia tsutsugamushi in humans, reservoir animals, and vectors in Puducherry, India

Provisionally accepted
Krishan  Kumar SihagKrishan Kumar Sihag1,2Waseema  AWaseema A3Srikanth  SriramaSrikanth Srirama1*Anand  Kumar ChandrasekaranAnand Kumar Chandrasekaran4Vinod  RaveendranVinod Raveendran5Asayas  Bosco ChandrakumarAsayas Bosco Chandrakumar6Anand  KasirajanAnand Kasirajan7Sivagamy  Alias Punitha ThavarajSivagamy Alias Punitha Thavaraj8Lakshmy  SrinivasanLakshmy Srinivasan1Anoop  C ChoolayilAnoop C Choolayil1Mathivanan  AshokkumarMathivanan Ashokkumar9Amala  RamasamyAmala Ramasamy10Panneer  DevarajuPanneer Devaraju1,2*
  • 1Unit of One Health, ICMR- Vector Control Research Centre (ICMR-VCRC), Indira Nagar, Puducherry, India
  • 2ICMR- Vector Control Research Centre (ICMR-VCRC), affiliated to Pondicherry University, Kalapet, Puducherry, India
  • 3Unit One Health, ICMR- Vector Control Research Centre (ICMR-VCRC), Indira Nagar, Puducherry, India
  • 4Indira Gandhi Medical College and Research Institute, Puducherry, India
  • 5Sri Venkateshwaraa Medical College Hospital and Research Centre, Ariyur, Puducherry, India
  • 6Sri Lakshmi Narayana Institute of Medical Sciences, Puducherry, India
  • 7Mahatma Gandhi Medical Advance Research Institute (MGMARI), Sri Balaji Vidyapeeth (Deemed to be University), Puducherry, India
  • 8ICMR- Vector Control Research Centre (ICMR-VCRC), Puducherry, Indira Nagar, Puducherry, India
  • 9Unit of Microbiology and Immunology, ICMR- Vector Control Research Centre (ICMR-VCRC), Puducherry, Indira Nagar, Puducherry, India
  • 10Unit of Biostatistics and VBD Modeling, ICMR- Vector Control Research Centre (ICMR-VCRC), Puducherry, Indira Nagar, Puducherry, India

The final, formatted version of the article will be published soon.

Background: Scrub typhus (ST), is a vector borne zoonotic disease, transmitted by the larva of the trombiculid mites. The enzootic cycle of the pathogen involves rodents/shrews as the animal reservoirs and humans are the accidental dead-end host. A transposon-like activity in its major antigen 56 kDa, has led to the evolution of several serotypes/strains, and more than 40 serotypes are reported globally. Puducherry, India, is endemic to scrub, but limited data exist on local serotype distribution across hosts. and vectors. Methodology: A longitudinal molecular surveillance was conducted in Puducherry to investigate the genetic diversity of O. tsutsugamushi among humans, animal reservoirs, and vectors. Samples from febrile patients, trapped rodents/shrews, and their infesting mites were screened using real-time and nested PCR. Serotype analysis was performed by partial amplification and sequencing of the 56 kDa gene, followed by phylogenetic, pairwise genetic distance and amino acid analysis. Result: ST infection was detected in 4.37% (95% CI: 3.05%-5.71%) of human, 11.52% (95% CI: 8.6%-14.4%) of rodent/shrew, and 2.36% (95% CI: 0.95%-4.87%) of mite samples. Karp-like (51.72%) and Gilliam-like (41.38%) strains were predominant in both humans and animal hosts, with pairwise genetic distance (<0.1) and amino acid identity (>85%) analysis revealing a close relationship between the strains identified across the region. Notably, the only mite pool that tested positive for the 56 kDa gene, along with a shrew, was identified to belong to the TA678-like serotype (6.90%), which has not been previously reported from Puducherry.This study provides molecular evidence of the enzootic maintenance and active human transmission of O. tsutsugamushi in Puducherry, with multiple co-circulating serotypes.The first detection of the TA678-like strain in the region suggests the possible introduction of new strains and underscores the need to monitor for strain-specific clinical manifestations in future studies

Keywords: Scrub Typhus, Molecular diagnostics, Genetic Heterogeneity, TA678-like strain, phylogenetic analysis

Received: 24 May 2025; Accepted: 05 Aug 2025.

Copyright: © 2025 Sihag, A, Srirama, Chandrasekaran, Raveendran, Chandrakumar, Kasirajan, Thavaraj, Srinivasan, Choolayil, Ashokkumar, Ramasamy and Devaraju. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Srikanth Srirama, Unit of One Health, ICMR- Vector Control Research Centre (ICMR-VCRC), Indira Nagar, Puducherry, India
Panneer Devaraju, Unit of One Health, ICMR- Vector Control Research Centre (ICMR-VCRC), Indira Nagar, Puducherry, India

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