The zoonotic rickettsial pathogen Anaplasma phagocytophilum has a broad geographical distribution and a high degree of biological and clinical diversity. To determine the prevalence of Anaplasma phagocytophilum in the Gannan Tibetan Autonomous Prefecture of Gansu Province, north-western China, four ruminant species, one rodent and one tick species were examined for Anaplasma phagocytophilum infection. DNA from Anaplasma phagocytophilum was detected by nested PCR in blood samples from 21/49 sheep (42.9 %), 35/91 goats (38.5 %), 51/158 yaks (32.3 %) and 7/20 cattle–yaks (35.0 %), and in spleen samples from 2/12 rodents (16.7 %). For samples from tick larvae and nymphs, 105 pools were tested; one of 46 larval tick pools was positive and seven of 59 nymphal tick pools were positive. For adult ticks, 40/598 female ticks (6.7 %) and 26/528 male ticks (4.9 %) were positive. The prevalence of Anaplasma phagocytophilum in female ticks was higher than that in males, although the difference was not statistically significant (P>0.05). Sequences analysis based on the 16S rRNA gene indicated that the strains in the study area were distinct from previously reported Anaplasma phagocytophilum in other continents. These results add new information on the epidemiology of Anaplasma phagocytophilum and indicate the tick–animal cycle of anaplasmosis in the area. To the best of our knowledge, this is the first report of Anaplasma phagocytophilum infection in Gansu Province in north-western China.
