Epidemiological Investigation and Phylogenetic Analysis of Major Blood-Derived Pathogens in Sheep from Gansu Province

Investigating the prevalence and molecular genetic characteristics of Anaplasma ovis, Theileria spp., Anaplasma phagocytophilum, and hemotropic Mycoplasma infections in sheep populations across different regions of Gansu Province is of significant importance for the prevention and control of these pathogens. A total of 1523 sheep blood samples were collected from 19 counties (districts) in Gansu Province. Pathogen screening was conducted using PCR-based molecular detection techniques, followed by sequencing and phylogenetic analysis of specific genes (e.g., Msp4, 18S rRNA) from selected positive samples. Blood-borne pathogens infections in Gansu Province were widespread but unevenly distributed geographically. Theileria spp. and Anaplasma ovis were the dominant pathogens, with overall infection rates of approximately 16.7% and 9.6%, respectively. The highest Anaplasma ovis infection rate (82.5%) was observed in the Gannan region, where co-infections were common (24/97). An exceptionally high Theileria spp. infection rate (87.5%) was detected in the Zagana area. No pathogens were detected in Wuwei, Jingyuan, Huining, Jingtai, Qinghuan, or Maqu. Phylogenetic analysis revealed that the Msp4 gene sequences of Anaplasma ovis isolates from Gansu shared 99.48% homology with strains from Europe, Asia, and Africa. Anaplasma phagocytophilum isolates also showed high homology (99.53-99.84%) with multiple global strains. Seasonal data indicated significantly higher Theileria spp. infection rates in spring (23-34%) compared to other seasons (approximately 12%). Gansu Province is an endemic area for multiple blood-borne pathogens, with distinct regional clustering and seasonality in prevalence. The high conservation of pathogen gene sequences suggests genetic stability. This study provides essential epidemiological baseline data and a scientific foundation for targeted prevention and control of blood-borne pathogen diseases in sheep in Gansu Province.