Evidence of the human granulocytic ehrlichiosis agent in Ixodes ricinus ticks in Switzerland

A total of 1,667 Ixodes ricinus ticks were collected from five regions in S witzerland where there have been sporadic occurrences of granulocytic ehrli chiosis in dogs and horses, The ticks were examined for rickettsiae of the Ehrlichia phagocytophila group via nested PCR, Twenty-one ticks (1.3%) were positive; 3 (0.5%) were nymphs, 6 (1.3%) were adult males, and It (1.9%) w ere adult females. The number of positive ticks varied with the stage of de velopment and with the geographical origin. Nucleotide sequencing of the is olated PCR products identified these products as part of the 16S rRNA gene of Ehrlichia. In addition, these products had 100% homology with the agent of human granulocytic ehrlichiosis, The occurrence of this agent in I. rici nus in Switzerland presents a potential danger of transmission of granulocy tic ehrlichiosis to dogs, horses, and humans.