Seroprevalence of Tick-Borne Anaplasma phagocytophilum Infection in Healthy Adult Population and Patients with Acute Undifferentiated Fever from the Yunnan Province of China

Anaplasma phagocytophilum-the causative agent of human granulocytic anaplasmosis (HGA)-is a tick-borne pathogen transmitted by Ixodid ticks infecting wild and domestic mammals as well as humans. Despite the availability of evidence regarding this emerging infection among vectors, host animals, and individuals in China, there is limited knowledge on the prevalence and distribution of A. phagocytophilum in the Yunnan Province. The aim of this study was to assess the seroprevalence of A. phagocytophilum in healthy adults and patients with acute undifferentiated fever from four regions in the Yunnan Province. The enzyme-linked immunosorbent assay and indirect immunofluorescence assay were used to detect immunoglobulin (Ig) G and IgM antibodies against A. phagocytophilum in sera obtained from 1185 healthy blood donors and 245 patients with acute undifferentiated fever, respectively. Demographic variables were assessed as potential risk factors using the chi-squared test. The rates of seropositivity rates were 7.59% and 4.49% in healthy donors and fever patients, respectively. Analysis of risk factors such as gender, age groups, and place of residence showed statistically significant differences. Infections with A. phagocytophilum occur widely among individuals residing in southwestern China. Our results indicate that there is serological evidence of HGA in this population and presence of acute A. phagocytophilum infections in patients with undifferentiated fever in the Yunnan Province.