Molecular Detection and Identification of Bacterial Pathogens in Qinghai Province, China.

As a core pastoral region of the Qinghai-Tibet Plateau, Qinghai Province faces substantial threats to livestock production from tick-borne diseases. This study aimed to investigate the prevalence of six bacterial pathogens in dominant tick species from Qinghai Province, to provide baseline epidemiological data for local tick-borne disease surveillance. A total of 1025 questing ticks were collected from key pastoral regions of Qinghai Province during April to May in 2024 and 2025. All ticks were morphologically identified as belonging to 1 family (Ixodidae), 2 genera, and 4 species. Dermacentor nuttalli was the dominant species with a relative dominance of 66.83% (685/1025, 95% CI: 63.92-69.61%), followed by Haemaphysalis qinghaiensis at 30.83% (316/1025, 95% CI: 28.11-33.69%), Dermacentor silvarum at 1.95% (20/1025, 95% CI: 1.27-2.98%), and Dermacentor niveus at 0.39% (4/1025, 95% CI: 0.15-1.01%). PCR detection was performed for six target pathogens, with an overall Brucella spp. DNA detection rate of 0.78% (8/1025, 95% CI: 0.40-1.53%) and an overall Rickettsia spp. detection rate of 16.29% (167/1025, 95% CI: 14.16-18.67%). Statistical analysis showed that the prevalence of Brucella spp. and Rickettsia spp. differed significantly between the two dominant tick species (Fisher's exact test/χ2 test, all p < 0.001). No Brucella or Rickettsia pathogens were detected in D. silvarum and D. niveus. Notably, detection of Brucella spp. DNA does not confirm the presence of viable bacteria or tick vector competence. This study fills the regional data gap of tick-borne pathogens in Qinghai, and provides reference for the prevention and control of local tick-borne zoonotic diseases.