High Diversity and Prevalence of Rickettsial Agents in Rhipicephalus microplus Ticks from Livestock in Karst Landscapes of Southwest China

Ticks and tick-borne pathogens pose a significant threat to human and animal health, yet the diversity and prevalence of tick-borne microorganisms in karst regions remains inadequately explored. In October 2023, a total of 274 <i>Rhipicephalus microplus</i> ticks were collected from livestock in Guizhou Province, which boasts the largest karst area in China. Pathogen identification was subsequently performed using PCR amplification, Sanger sequencing, and phylogenetic analysis. High microbial diversity was noted, with five bacterial species from the order Rickettsiales detected, including those from the genera <i>Rickettsia</i> (family <i>Rickettsiaceae</i>), <i>Anaplasma</i>, and <i>Ehrlichia</i> (family <i>Anaplasmataceae</i>). The overall prevalence of infection with at least one pathogen was remarkably high at 94.5%. The highest positive rate was observed for <i>Candidatus</i> Rickettsia jingxinensis at 90.9%. A novel <i>Ehrlichia</i> species, provisionally designated as <i>Candidatus</i> Ehrlichia carsus, was identified with a positive rate of 16.8%. In addition, <i>Anaplasma marginale</i>, <i>Ehrlchia minasensis</i> and <i>Ehrlichia canis</i> were detected in 15.3%, 4.7% and 1.5%, respectively. The co-infections involving two or three rickettsial species were observed in 34.3% ticks. These findings highlight the high diversity and prevalence of tick-borne rickettsial agents in the karst area, underscoring the need for enhanced surveillance and effective tick control to mitigate disease risks to both humans and livestock.