Parallel Molecular Surveillance Reveals <em>Rickettsia </em>spp. in <em>Haemaphysalis longicornis</em> Ticks and a Novel Finding of <em>Legionella pneumophila</em> in <em>Spermophilus dauricus</em> Rodents in China

Background: Ticks and rodents are significant vectors and reservoirs of zoonotic pathogens, posing considerable threats to public health. However, comprehensive data on the distribution and diversity of pathogens across different host types in key regions of China remain limited. This study employed a parallel surveillance strategy to investigate pathogen landscapes in Haemaphysalis longicornis ticks, and Spermophilus dauricus rodents from distinct geographical areas in Northeast and East-Central China. Methods: Questing H. longicornis ticks (n=1,004, processed in 670 pools) were collected from Liaoning and Anhui provinces, while liver tissues from S. dauricus rodents (n=42) were sampled in Heilongjiang province. Host species were confirmed using cytochrome oxidase I (COI) gene sequencing. Nucleic acids from all samples were screened for Dabie bandavirus (formerly SFTSV) and bacteria using universal 16S rRNA gene primers. Bacterial-positive samples were subsequently tested for specific pathogens using multi-gene nested PCR assays. Phylogenetic analyses, including supertree construction from concatenated gene sequences, were performed to ensure robust species identification and explore genetic relationships. Results: Spotted Fever Group Rickettsia (SFGR) were detected in 14/670 tick pools, yielding a Minimum Infection Rate (MIR) of 1.4% (14/1,004). This included Candidatus Rickettsia jingxinensis in Liaoning (MIR 2.0%) and Rickettsia heilongjiangensis in Anhui (MIR 2.6%). Additionally, Coxiella-like endosymbionts (CLE) were found in 20 tick pools. Strikingly, Legionella pneumophila DNA was detected in 2/42 (4.8%) S. dauricus liver samples. Phylogenetic analysis revealed these L. pneumophila sequences were highly homologous to a known human pathogenic strain (OLDA). No Dabie bandavirus was detected. Conclusions: Our parallel surveillance provides a valuable snapshot of regional pathogen distribution. We confirm the circulation of distinct SFGR species in H. longicornis ticks in Liaoning and Anhui. The novel detection of pathogenic L. pneumophila DNA in S. dauricus tissues suggests these rodents, may serve as effective environmental sentinels for this important human pathogen. These findings underscore the need for integrated surveillance across diverse host species to better assess public health risks.