Case Report: Polymerase Chain Reaction Testing of Tick Bite Site Samples for the Diagnosis of Human Granulocytic Anaplasmosis.

Human granulocytic anaplasmosis (HGA) is a tick-borne infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium. Until now, the utility of tick-bite site samples for HGA diagnosis has not been reported. Using a patient's buffy coat and tick-bite site crust samples, we performed polymerase chain reaction (PCR) testing using Ehrlichia- or Anaplasma-specific primers. PCR with buffy coat and crust samples obtained before doxycycline administration was positive. Six days after doxycycline administration, PCR with the buffy coat sample was negative but PCR with a crust tissue sample from the tick-bite site remained positive. This is the first case to suggest that crust tissue at the tick-bite site may be useful for early HGA diagnosis in patients who have already been treated with antibiotics such as doxycycline.