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

Investigating the prevalence and molecular genetic characteristics of <i>Anaplasma ovis</i>, <i>Theileria</i> spp., <i>Anaplasma phagocytophilum</i>, and hemotropic <i>Mycoplasma</i> 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. <i>Theileria</i> spp. and <i>Anaplasma ovis</i> were the dominant pathogens, with overall infection rates of approximately 16.7% and 9.6%, respectively. The highest <i>Anaplasma ovis</i> infection rate (82.5%) was observed in the Gannan region, where co-infections were common (24/97). An exceptionally high <i>Theileria</i> 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 <i>Anaplasma ovis</i> isolates from Gansu shared 99.48% homology with strains from Europe, Asia, and Africa. <i>Anaplasma phagocytophilum</i> isolates also showed high homology (99.53-99.84%) with multiple global strains. Seasonal data indicated significantly higher <i>Theileria</i> 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.