Borrelia burgdorferiSensu Lato andEhrlichiaspp. inIxodesTicks from Southern Norway

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Abstract
We report the results of a study of the prevalence ofEhrlichiaandBorreliaspecies in 341 questingIxodes ricinusticks from two locations in southern Norway. The prevalences ofBorrelia burgdorferisensu lato andEhrlichiaspp. were, respectively, 16 and 11.5% at site 1 and 17 and 6% at site 2. Prevalence and species composition ofBorreliaandEhrlichiavaried with location and date of collection. The dominantBorreliaspecies at both sites wasBorrelia afzelii, followed byBorrelia burgdorferisensu stricto.Borrelia gariniiwas found in only a single tick. The dominant member of theEhrlichiagroup was a recently describedEhrlichia-like organism related to the monocytic ehrlichiae. Variants ofEhrlichia phagocytophilaand the agent of human granulocytic ehrlichiosis were also found. The highest prevalences forB. afzelii,B. burgdorferisensu stricto, and theEhrlichia-like organism were observed in May.B. afzeliiwas most prevalent in females, less prevalent in nymphs, and least prevalent in males, while the prevalence ofEhrlichiawas highest in nymphs, lower in females, and least in males. Double infections withB. afzeliiandB. burgdorferisensu stricto and withB. afzeliiand theEhrlichia-like organism were significantly overrepresented. Tick densities were highest in May, when densities of more than 200 ticks/100 m2were observed, and declined during the summer months to densities as low as 20 ticks/100 m2. We conclude that estimates of the prevalence of tick-borne bacteria are sensitive to the choice of date and site for collection of ticks. This is the first study of tick-borneBorreliaandEhrlichiain Norway and the lowest reportedB.gariniiprevalence in Northern Europe. The prevalence of theEhrlichia-like organism is described for the first time in questing ticks.