Rural Residents in China Are at Increased Risk of Exposure to Tick-Borne PathogensAnaplasma phagocytophilumandEhrlichia chaffeensis

As emerging tick born rickettsial diseases caused byA. phagocytophilumandE. chaffeensis, anaplasmosis and ehrlichiosis have become a serious threat to human and animal health throughout the world. In particular, in China, an unusual transmission of nosocomial cases of human granulocytic anaplasmosis occurred in Anhui Province in 2006 and more recent coinfection case ofA. phagocytophilumandE. chaffeensiswas documented in Shandong Province. Although the seroprevalence of human granulocytic anaplasmosis (former human granulocytic ehrlichiosis, HGE) has been documented in several studies, these data existed on local investigations, and also little data was reported on the seroprevalence of human monocytic ehrlichiosis (HME) in China. In this cross-sectional epidemiological study, indirect immunofluorescence antibody assay (IFA) proposed by WHO was used to detectA. phagocytophilumandE. chaffeensisIgG antibodies for 7,322 serum samples from agrarian residents from 9 provinces/cities and 819 urban residents from 2 provinces. Our data showed that farmers were at substantially increased risk of exposure. However, even among urban residents, risk was considerable. Seroprevalence of HGA and HME occurred in diverse regions of the country and tended to be the highest in young adults. Many species of ticks were confirmed carryingA. phagocytophilumorganisms in China while several kinds of domestic animals including dog, goats, sheep, cattle, horse, wild rabbit, and some small wild rodents were proposed to be the reservoir hosts ofA. phagocytophilum. The broad distribution of vector and hosts of theA. phagocytophilumandE. chaffeensis, especially the relationship between the generalized susceptibility of vectors and reservoirs and the severity of the disease’s clinical manifestations and the genetic variation of Chinese HGA isolates in China, is urgently needed to be further investigated.