Anaplasma phagocytophilum is a tick-transmitted obligate-intracellular gram-negative bacteria that causes emerging human zoonosis. A. phagocytophilum is transmitted by Ixodid ticks. Recent studies suggest that wild animals may be reservoirs of A. phagocytophilum for humans. The organism infects and survives within neutrophils. The infection diagnosis is based on the detection of morulae within granulocytes of peripheral blood, results of serological tests and detection of the DNA of A. phagocytophilum using specific polymerase chain reaction assays (PCR). A. phagocytophilum in most cases is transmitted to people by tick bites, but sometimes direct contact with infected blood may cause human granulocytic anaplasmosis (HGA). The possibility of infection should be taken into consideration at each occurrence of heavy disease symptoms after people come into contact with ticks.