Sihag Krishan Kumar, Arif Waseema, Srirama Srikanth, Chandrasekaran Anand Kumar, Raveendran Vinod, Chandrakumar Asayas Bosco, Kasirajan Anand, Thavaraj Sivagamy Alias Punitha, Srinivasan Lakshmy, Choolayil Anoop C, Ashokkumar Mathivanan, Ramasamy Amala, Yellapu Nanda Kumar, Devaraju Panneer
Unit of One Health, ICMR-Vector Control Research Centre (ICMR-VCRC), Indira Nagar, Puducherry, India.
ICMR-Vector Control Research Centre (ICMR-VCRC), Affiliated to Pondicherry University, Kalapet, Puducherry, India.
Front Microbiol. 2025 Aug 29;16:1634394. doi: 10.3389/fmicb.2025.1634394. eCollection 2025.
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.
A longitudinal molecular surveillance was conducted in Puducherry to investigate the genetic diversity of 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.
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 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.
恙虫病是一种由恙螨幼虫传播的媒介传播人畜共患病。病原体的动物疫源循环涉及啮齿动物/鼩鼱作为动物宿主，而人类是偶然的终末宿主。其主要抗原56 kDa中存在类似转座子的活性，导致了几种血清型/菌株的进化，全球报道的血清型超过40种。印度本地治里流行恙虫病，但关于当地宿主和媒介中血清型分布的数据有限。
在本地治里进行了一项纵向分子监测，以调查人类、动物宿主和媒介中恙虫病的遗传多样性。使用实时荧光定量PCR和巢式PCR对发热患者、捕获的啮齿动物/鼩鼱及其身上寄生的恙螨样本进行筛查。通过对56 kDa基因进行部分扩增和测序进行血清型分析，随后进行系统发育分析、成对遗传距离分析和氨基酸分析。
在人类样本中，4.37%（95%置信区间：3.05 - 5.71%）检测到恙虫病感染；在啮齿动物/鼩鼱样本中，11.52%（95%置信区间：8.6 - 14.4%）检测到感染；在恙螨样本中，2.36%（95%置信区间：0.95 - 4.87%）检测到感染。卡尔普型（51.72%）和吉列姆型（41.38%）菌株在人类和动物宿主中均占主导地位，成对遗传距离（<0.1）和氨基酸同一性（>85%）分析表明该地区鉴定出的菌株之间关系密切。值得注意的是，唯一检测到56 kDa基因呈阳性的恙螨样本池，连同一只鼩鼱，被鉴定属于TA678型血清型（6.90%），此前在本地治里尚未有过报道。
本研究提供了分子证据，证明本地治里存在恙虫病的动物疫源维持和人类的活跃传播，且有多种血清型共同流行。该地区首次检测到TA678型菌株表明可能引入了新菌株，并强调在未来研究中需要监测菌株特异性临床表现。
