Sur vey of Tickbor ne Infections in Denmark Sigurdur Skarphédinsson,* Per M. Jensen,† and Kåre Kristiansen‡ We conducted a study of the distribution and preva- lence of tickborne infections in Denmark by using roe deer as sentinels. Blood samples from 237 roe deer were col- lected during the 2002–2003 hunting season. Overall, 36.6% of deer were Borrelia seropositive, while 95.6% were Anaplasma phagocytophilum positive; all animals were negative for Bartonella quintana and B. henselae by indirect immunofluorescence assay. When a hemagglutina- tion-inhibition test was used, 8.7% of deer were found pos- itive for tickborne encephalitis (TBE)-complex virus. A total of 42.6% were found positive by polymerase chain reaction (PCR) for A. phagocytophilum with significant seasonal variation. All were PCR negative for Rickettsia helvetica. PCR and sequencing also showed a novel bacterium in roe deer previously only found in ticks. The study showed that the emerging pathogen A. phagocytophilum is widely dis- tributed and that a marked shift has occurred in the distri- bution of TBE-complex virus in Denmark. This finding supports studies that predict alterations in distribution due to climatic changes. Aborne infections may be among the first signs of the change in the distribution and frequency of vector- effect of global climatic change on human health (1). Tickborne infections are the most frequent human vector- borne infections in Europe; the incidence of many of these diseases has been on the rise, and new infections have emerged. In Denmark, borreliosis is known to be endemic and widespread, while tickborne encephalitis (TBE) has been found only on the island of Bornholm. In recent years, human serosurveys have indicated that granulocytic ehrlichiosis caused by Anaplasma phagocytophilum is also found in Denmark (2); however, the distribution is unclear. Studies on Ixodes ricinus ticks have revealed the existence of other potential pathogens, among them Rickettsia hel- vetica and Bartonella spp. (3, S. Skarphédinsson et al., *University of Southern Denmark, Odense, Denmark; †The Royal Veterinary and Agricultural University, Fredriksberg, Denmark; and ‡Medical Public Health Office, Rønne, Denmark unpub. data). At the same time, increase in the incidence of TBE has been noted in neighboring countries like Germany, Poland, Lithuania, and Sweden (4). Changes in the distribution of TBE in Europe have been suggested to be related to climatic changes, and new foci have been pre- dicted, some within Denmark (5). However, the role of cli- matic changes is unclear, and increased surveillance is needed to elucidate this in further detail. I. ricinus is the main vector of tickborne infections in Europe and the dominant tick in Denmark (>90%). Roe deer (Capreolus capreolus), an important host for I. ricinus ticks, have been used as sentinel animals to monitor tick- borne infections in several studies, 2 of which have been performed in Denmark. In 1963, Freundt published a sur- vey of TBE (6), and in 1994 Webster and Frandsen evalu- ated the seroprevalence of Borrelia burgdorferi in deer (7). In light of increasing tick density observed, as well as the finding of new pathogens in Denmark, reassessment is indicated (8). The aim of this study was to assess the sero- prevalence and geographic distribution of TBE-complex virus, Borrelia burgdorferi, A. phagocytophilum, Bartonella quintana, and Bartonella henselae by using roe deer as natural sentinels; at the same time, we evaluated prevalence of infection with A. phagocytophilum and R. helvetica by using polymerase chain reaction (PCR). Materials and Methods Sample Collection and Serologic Testing State forest rangers from the 25 Danish state forest dis- tricts were invited to participate during the regular hunting season of 2002 (May 15–July 15, 2002 [summer], and October 1, 2002–January 15, 2003 [fall]). They were asked to obtain blood samples from roe deer by cardiac puncture or from the thoracic cavity when dressing freshly killed animals in the field. For each animal, sex, age, and degree of tick infestation was also noted. Blood collection kits were distributed to all state forest districts by mail, and Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 7, July 2005 1055