TBE in Denmark

Since the 1950s, tick-borne encephalitis (TBE) has been known to be endemic in Denmark but only on the island of Bornholm. Bornholm is situated east of mainland Denmark, south of Sweden (Figure 3) and has a different fauna and flora from the rest of Denmark. Bornholm has about 45,000 inhabitants, but about 500,000 tourists visit the island every year. Freundt carried out a serosurvey during 1958–1962 and found TBE antibodies in 1.4% of blood donors and 30% of woodworkers on Bornholm but no antibodies in subjects living in mainland Denmark. In 1963, Freundt found that 8 of 12 patients admitted to the hospital with acute meningoencephalitis of unknown etiology during 1951–1960 had antibodies to tick-borne encephalitis (TBEV). In 2000, TBE was rediscovered on Bornholm, where a retrospective study covering the period 1994–2002 (7 years) identified 14 TBE cases; 2 cases were tourists and 12 were inhabitants of Bornholm, giving an incidence of 3.81 per 100,000 inhabitants. At least 5 patients (37.7%) got permanent sequelae. In addition, 32 forest workers on Bornholm were tested in 2000, and 20% had IgG antibodies but never symptoms. This is similar to the finding of Freundt in 1960. It was concluded that the data did not provide evidence of an increase in incidence of TBE. Ticks (Ixodes ricinus) from Bornholm were investigated for TBEV in 2000 and 2% were found to be infected. Since 2001 an average of 2.5 (range 1–8) TBE cases per year have been reported in Bornholm (Figure 1).