Spotted fever Rickettsia and relapsing fever Borrelia in rodents from southern India.

UNLABELLED: Bacterial zoonoses constitute a significant proportion of emerging infectious diseases. Yet, the diversity and transmission cycles of many zoonotic bacteria remain poorly characterized, particularly in tropical, biodiverse regions where host and vector diversity are high, and the burden of zoonotic disease in human populations is substantial. In this study, we investigated the presence of five pathogenic bacterial genera-Rickettsia, Borrelia, Orientia, Leptospira, and Coxiella-in rodents from southern India. We detected low circulation of Rickettsia (7.26%), Borrelia (6.45%), and Leptospira (0.8%), with limited coinfections, whereas Orientia and Coxiella were not detected in the rodents sampled. Notably, we observed contrasting patterns of tissue association, with rickettsiae detected exclusively in pooled organ tissues and borreliae detected only in blood, suggesting the influence of pathogen biology in detection probabilities. Our phylogenetic analyses further confirmed that the detected Rickettsia and Borrelia belonged to the spotted fever group rickettsiae and relapsing fever group borreliae, respectively, in both synanthropic and forest-associated rats, highlighting a potential transmission risk to people and livestock in the region. By revealing the circulation of zoonotic bacteria in new host species, this study underscores the need for systematic surveillance of wildlife to better characterize bacterial diversity and its public health implications.

IMPORTANCE: Many bacterial infections affecting humans originate in wild and synanthropic rodents, making it essential to characterize bacterial diversity in these hosts to predict and mitigate zoonotic risk. This study provides a molecular assessment of five pathogenic bacterial genera, including Rickettsia and Borrelia, in a rodent community in southern India, addressing a key geographic and taxonomic knowledge gap. By detecting low but persistent circulation of spotted fever group rickettsiae and relapsing fever group borreliae, our findings demonstrate that even low-prevalence systems can harbor epidemiologically significant diversity. Importantly, shared Borrelia lineages between forest and synanthropic rodents highlight potential pathways for transmission across habitat boundaries and human exposure. Additionally, the detection of novel borreliae suggests that bacterial diversity in tropical wildlife communities is still poorly understood. Collectively, this study advances our understanding of zoonotic bacterial diversity in a biodiverse region and provides a foundation for improving wildlife surveillance and zoonotic risk assessment.