Presence of granulocytic ehrlichia in ticks and serological evidence of human infection in La Rioia, Spain

In order to estimate the risks of human granulocytic ehrlichiosis (HGE) in an endemic area for Lyme disease in the North of Spain (La Rioja), we collected and investigated by PCR specific to the E. phagocytophila group DNA, a total of 6870 Ixodes ricinus ticks. We also used an indirect immunofluorescence (IFI) test to study the presence of antibodies to the HGE agent in 147 human serum samples including patients with Lyme disease (LD), forestry workers, and persons with history of previous tick bite. Fifty serum samples from healthy people resident in urban areas and with no history of tick-bite disorder and without tick exposure were used as controls. Four of 76 adults and 49 of 203 nymphs pools carried E. phagocytophila DNA. This result, and the finding of 1.4% of sera reacting in the IFI test confirms that this tick-borne agent is present in La Rioja, and that humans show evidence of contact with it. HGE should be considered in the differential diagnosis of flu-like syndromes in the study area in the north of Spain.