Tickborne Infections in Denmark Further characterization of European strains of A. phago- competent as reservoirs or that the bacteremic phase is cytophilum is needed; the finding of a high A. phagocy- very short. Another possibility is that R. helvetica has a tophilum prevalence in roe deer compared to the low very focal distribution or is even disappearing from number of human anaplasmosis cases reported in Europe Denmark, as the seroprevalence study of Nielsen et al. may indicate the existence of strains less virulent or non- showed a gradual decrease in seroprevalence from 29% in pathogenic to humans (26). The finding of sequences in 1997 to 0% in 2000 (3). roe deer blood that are related to sequences previously Tickborne encephalitis was the first tickborne infection amplified only from ticks in Italy (It86-Belluno) is of inter- to be recognized in Denmark. During the years est and should be studied further (27). Whether this organ- 1958–1962, E.A. Freundt did a survey for TBE-complex ism is pathogenic to roe deer or can cause human infection virus using human and animal sera from all parts of remains to be elucidated. The accuracy of diagnostic Denmark. He found, using both HI, neutralization, and assays used is critical to any pathogen surveillance, and the complement fixation tests, that TBE-complex virus was potential for serologic cross-reaction is an important con- present only on the island of Bornholm. He found an over- sideration. Recently R. helvetica has been found in ticks all seroprevalence of 8.6% in Danish roe deer (the local from Bornholm and Jutland, and a seroprevalence of seroprevalence on Bornholm was 83%) (6). Since then a 12.5% was described in high-risk groups in northern very limited surveillance of TBE has since been carried out Jutland (3, S. Skarphédinsson et al., unpub. data). Even in Denmark. Recent increases in TBE cases in neighboring though it is not phylogenetically close to A. phagocy- Sweden have been suggested to be related to climatic tophilum, and even though serologic cross-reactivity has changes (28), as milder climate has been followed by a not been reported to date, it is the only other Rickettsia northern shift in the distribution limit of I. ricinus as well species reported in Denmark. We therefore looked for R. as a general increase in tick density (29). However, the helvetica in roe deer, but found no PCR-positive deer. The variable patterns of changing TBE case numbers in Europe explanation for this finding may be that roe deer are not indicate that changing climate is not the sole causal factor. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 7, July 2005 1059